Bioimpedance Measurement
17
Bioimpedance Measurement Dept. of Biomedical Engineering 2003200449 YOUNHO HONG
description
Dept. of Biomedical Engineering 2003200449 YOUNHO HONG. Bioimpedance Measurement. Impedance measure. i=0. measured. known. i=0. constant current source. +. reactance. Z. impedance. resistance. -. Impedance measure. (Example). Im. 1. 1+j. 1. Re. - PowerPoint PPT Presentation
Transcript of Bioimpedance Measurement
Bioimpedance MeasurementDept. of Biomedical Engineering
2003200449YOUNHO HONG
Impedance measure
IR A v =1
V =R i
+
-
O U T
constantcurrentsource
i=0
i=0measured
knowni
VR
Z0II
+
-
IZ
V
V jXR Zimpedance resistance
reactance
Impedance measure(Example) 1000HzFreq. , ][ 4521 jZ
1
1
1+j
Re
Im
)}8000
1(10002sin{2
)4
10002sin(2)(452
)10002sin()( [mA] 01
t
ttV
tti
IZV
I
i V
t
1 You are given with i(t) = I sin(2πft)You measure v(t) = V sin(2πft+θ)
ZI
V
I
VZ
Impedance measure(Example)
R C Z
)()()1
(1
11
1
222
2
222wjXwR
CRw
CwRj
CRw
R
jwRC
R
jwCR
jwCR
Z )(tan 1 wRCR Z
Impedance measure
R
C
R 1 C
R 2
)()()1
(1
wjXwRwC
jRjwC
R
Z
)1
(tan1
21
222
RCwCwR Z
ZwjXwR
CRW
CwRj
CRw
RR
)()(
)1
(1 22
12
21
221
21
2Z
Impedance measure
I
D if f e re n t ia l A M P
+
-
O U TZ X
X
T
I dttVT 0
)(1
T
Q dttVT 0
)(1
?
?
sin(2πft)
cos(2πft)
phase-sensitive Demodulation
Impedance measure
)}22cos({cos2
)2sin()2sin()2sin()()(
ftV
ftftVfttVtVI
I
T
I
VV
TT
VdttV
T
2
1cos
2
)(cos1
2)(
10
In-phase Component
cosVVI
Impedance measure
Quadrature Component
}sin)22{sin(2
)2cos()2sin()2cos()()(
ftV
ftftVfttVtVQ
Q
T
Q
VV
TT
VdttV
T
2
1sin
2
)(sin1
2)(
10
sinVVQ
Impedance measure
2222222 cossin VVVVV QI
22QI VVV
tancos
sin
V
V
V
V
I
Q
I
O
V
V1tan
sincos jZZjXRZ Z
Vsin θ
Vcosθ Re
Im
V
θ
(In-phase Component)
(Quadrature Component)
V=VI+jVQ
Two-electrode Method
V
I
skin
electrodeequivalent circuit
R c
R sE h c
C c
i
E h 1 E h 2
V
ZC1 ZC2
Zb
Inject current and then measure voltage
2211 )( EhEh CbC IZZZV
Two-electrode Method)sin()sin()sin()( 221121 wtIZwtIZwtIZEhEhtV CbbC
Component) phase-(In coscoscos
sin)(1
2
2211
0
IZIZIZ
dtwttVT
V
CbbC
T
I
Component) e(Quadratur sinsinsin 2211 IZIZIZV CbbCQ
Re
Im
ZbcosθbZc1cosθ1Zc2cosθ2
Zc1sinθ1
Zc2sinθ2
Zbsinθb
impedance)body (contact
sincos
sincos
sincos
21
2222
1111
CbC
CC
bbbb
CC
QI
jZZ
jZZ
jZZI
jVV
ZZZ
Z
Four-electrode Method
V
I
skin
E1 E3 E4 E2
i
E h 1 E h 3E h 4
E h 2
ZC1 ZC3
Zb1 Zb2
ZC4 ZC2
Zb
0I IIZV b
sincos)(1
2
cossin)(1
2
)sin()(
0
0
IZdtwttVT
V
IZdtwttVT
V
wtIZtV
b
T
Q
b
T
I
bb
impedance)body (only
sincos
b
bbbb
QIm
jZZI
jVV
Z
Z
Three-electrode Method
V
I
skin
E1 E3 E2
i
E h 1 E h 3 E h 2
ZC1 ZC3 ZC2
Zb1 Zb
2
22
22
sinsin
coscos
Cb
CCbb
CCbb
QIm
jZjZ
ZZI
jVV
ZZ
Z
We can measure skin impedanceusing Three and Four electrode Method
2
)()(
C
mm MethodfourMethodthree
Z
ZZ
Noise Effect
)()sin()()()( tnwtZItntVtVm
coscos
sin)(2
sin)sin(2
sin)(1
2
00
0
f
TT
T
mmI
NZI
dtwttnT
dtwtwtZIT
dtwttVT
V
Spectrum AnalizertwAtwAtwAtV NN sin.....sinsin)( 2211
A1A3A2
f1
AN
f2 f3 fN…
…
X
X
1
01
1 Tdt
T
2
02
1 Tdt
T
sinw1t / cosw1tV(t)
X NT
N
dtT 0
1
…
…sinw2t / cosw2t
sinwNt / coswNt
2,
211 BA
2,
222 BA
2,
2NN BA
T
nn dttwtVA0
sin)(
“ DFT “
Bio Impedance Spectroscophy
Z
+
-
I
VZ b
Repeat measurement for many frequencies
Zb
f
θ f
Thank you.
