Chapter 11 ndash Magnetic Circuits

Lecture 5

by Moeen Ghiyas

200423 1

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 3

200423 4

Example ndash The electromagnet

of fig has picked up a section

of cast iron Determine the

current I required to establish

the indicated flux in the core

Solution

200423 5

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 3

200423 4

Example ndash The electromagnet

of fig has picked up a section

of cast iron Determine the

current I required to establish

the indicated flux in the core

Solution

200423 5

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 3

200423 4

Example ndash The electromagnet

of fig has picked up a section

of cast iron Determine the

current I required to establish

the indicated flux in the core

Solution

200423 5

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 4

Example ndash The electromagnet

of fig has picked up a section

of cast iron Determine the

current I required to establish

the indicated flux in the core

Solution

200423 5

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash The electromagnet

of fig has picked up a section

of cast iron Determine the

current I required to establish

the indicated flux in the core

Solution

200423 5

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 6

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 7

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 8

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 9

Anology of circuits

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Determine the secondary current I2 for the

transformer of fig if the resultant clockwise flux in the core is

15 x 10-5 Wb

Solution

200423 10

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Solution

200423 11

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Solution

200423 12

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Solution

200423 13

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

The spreading of the flux lines outside the common area of

the core for the air gap in fig (a) is known as fringing

Neglect this effect of fringing as shown in fig (b)

The flux density of air gap is given by

Where

200423 14

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

For most practical applications the permeability of air is

taken to be equal to that of free space The magnetizing

force of the air gap is then determined by

and the mmf drop across the air gap is equal to Hglg An

equation for Hg is as follows

200423 15

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the value of I required to establish a

magnetic flux of φ = 075 x 10-4 Wb in the series magnetic

circuit of fig

Solution

200423 16

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the value of I φ = 075 x 10-4 Wb

Solution

200423 17

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Determine the current I required to establish a

flux of φ =15 x 10-4 Wb in the section of the core indicated

in fig

Solution

200423 18

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Here NI is given and the flux φ must be found

This is a relatively straightforward problem if only one

magnetic section is involved Then

For magnetic circuits with more than one section there is

no set order of steps that will lead to an exact solution for

every problem on the first attempt

200423 19

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

We must find the impressed mmf for a calculated guess of

flux φ and then compare this with specified value of mmf

For most applications a value within plusmn5 of the actual Φ

or specified NI is acceptable

We can make a reasonable guess at the value of Φ if we

realize that the maximum mmf drop appears across the

material with the smallest permeability if the length and

area of each material are the same

200423 20

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Calculate the magnetic flux Φ for the magnetic

circuit of fig

Solution

200423 21

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the magnetic flux Φ for the series

magnetic circuit of fig for the specified impressed mmf

Solution

200423 22

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the magnetic flux Φ

Solution

200423 23

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the magnetic flux Φ

Solution

200423 24

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Example ndash Find the magnetic flux Φ

Solution

200423 25

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Recording System

The basic recording process is same as in computer hard

disks

0003 m2

A

1048576

200423 26

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Speakers and Microphones

Electromagnetic effects used as moving force in speaker design

As the current peaks and returns to the valleys of the sound

pattern the strength of the electromagnet varies in exactly the

same manner This causes the cone of the speaker to vibrate at a

frequency directly proportional to the pulsating input

200423 27

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Speakers and Microphones

A second design used more frequently in more expensive speaker

system using permanent magnet High peaking currents at the input

produce a strong flux pattern in the voice coil causing it to be drawn

well into flux pattern of permanent magnet

200423 28

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Speakers and Microphones

Dynamic microphones such as above also employ

electromagnetic effects The sound to be reproduced at a higher

audio level causes the core and attached moving coil to move

within the magnetic field of the permanent magnet

Through Faradayrsquos law (e = N dΦdt) a voltage is induced

across the movable coil proportional to the speed with which it is

moving through the magnetic field The resulting induced

voltage pattern can then be amplified and reproduced at a much

higher audio level through the use of speakers

200423 29

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

The computer hard disk stores data on a magnetic coating applied to the

surface of circular platters that spin like a record The platters are

constructed on a base of aluminium or glass (both nonferromagnetic)

which makes them rigidmdashhence the term hard disk

The magnetic coating on the platters is called the media and is of either

the oxide or the thin-film variety

200423 30

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

The information on a disk is stored around the disk in circular paths called

tracks or cylinders

In its simplest form the writeread head of a hard disk (or floppy disk) is a

U-shaped electromagnet with an air gap that rides just above the surface

of the disk

200423 31

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

As the disk rotates information in the form of a voltage with changing

polarities is applied to the winding of the electromagnet

If we energize a positive voltage level with a 1 level (of binary arithmetic)

and a negative voltage level with a 0 level the resulting magnetic flux

pattern will have the direction shown in the core

200423 32

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

When the flux pattern encounters the air gap of the core it jumps to the

magnetic material (since magnetic flux always seeks the path of least

reluctance and air has a high reluctance) and establishes a flux pattern

as shown on the disk until it reaches the other end of the core air gap

where it returns to the electromagnet and completes the path

200423 33

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

As the head moves to the next bit sector it leaves behind the

magnetic flux pattern just established from the left to the right

200423 34

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Computer Hard Disks

Data reading is done by a significant change in flux occurs when the

head passes over the transition region causing a measurable voltage to

be generated across the terminals of the pickup coil as dictated by

Faradayrsquos law

200423 35

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Hall Effect Sensors

The Hall effect sensor is a semiconductor device that generates an

output voltage when exposed to a magnetic field

If a magnetic field is applied as perpendicular to the direction of the

current a voltage VH will be generated between the two terminals

200423 36

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Hall Effect Sensors

The force causes the electrons to accumulate in the bottom region of

the semiconductor (connected to the negative terminal of the voltage

VH) leaving a net positive charge in the upper region of the material

(connected to the positive terminal of VH)

The stronger the current or strength of the magnetic field the greater

the induced voltage VH

200423 37

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Hall Effect Sensors

The most widespread use of hall effect is as a trigger for an alarm

system in large department stores where theft is often a difficult

problem

A magnetic strip attached to the merchandise sounds an alarm when a

customer passes through the exit gates without paying for the product

The sensor control current and monitoring system are housed in the

exit fence and react to the presence of the magnetic field as the product

leaves the store

When the product is paid for the cashier removes the strip or

demagnetizes the strip by applying a magnetizing force that reduces the

residual magnetism in the strip to essentially zero200423 38

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Magnetic Reed Switch

200423 39

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

The three major components of an MRI system are a huge

magnet that can weigh up to 100 tons a table for transporting

the patient into the circular hole in the magnet and a control

200423 40

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

A strong magnetic field that causes the nuclei of certain atoms in the

body to line up

Radio waves of different frequencies are then applied to the patient in

the region of interest and if the frequency of the wave matches the

natural frequency of the atom the nuclei will be set into a state of

resonance and will absorb energy from the applied signal

200423 41

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Magnetic Resonance Image (MRI or NMR vs CAT Scans)

When the signal is removed the nuclei release the acquired energy in

the form of weak but detectable signals The strength and duration of

the energy emission vary from one tissue of the body to another The

weak signals are then amplified digitized and translated to provide a

cross-sectional image

200423 42

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

Review

Amperersquos Circuital Law ndash (Applying KVL)

The Flux Φ ndash (Applying KCL)

Series Magnetic Circuits

Air Gaps

Series-Parallel Magnetic Circuits

Determining Flux Φ

Applications

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 44

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 45

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46

200423 46

• TODAYrsquoS LECTURE CONTENTS
• Amperersquos Circuital Law ndash (KVL)
• The Flux Φ ndash (KCL)
• Series Magnetic Circuits
• Series Magnetic Circuits
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Air Gaps
• Slide 15
• Air gaps
• Slide 17
• Series ndash Parallel Magnetic Circuits
• Determining flux φ
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Applications ndash Magnetic Circuits
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Summary Conclusion
• Slide 44
• Hysteresis
• Slide 46