Conductive fabrics

Current flow in fabrics depends on..

- conductive material used

- % of conductive fibers

- fabric structure

- conductive fiber contact surface

Conductive Fibers

- metals – copper, silver, stainless steel, brass, Monel (Nickel)

- metallized fibers - polyamide/silver

- carbon

Metal fibers (1)

single filament - from 25μm up

Multifilament – braided, twisted/strandedfilaments as low as 50μm

Pure metals

They are made using cable production technologies

They are referred to as: wires

braided stranded

copper can be

bare = conductive surface

tinned = conductive, protected against oxidation

coated = non conductive surface

Metal fibers (2)

multifilament – spun yarnsfilaments as low as 8μm for stainless steel

Pure metals

They are produced using textile production technologies

They are referred to as: yarns

Metal fibers (2)

multifilament – spun yarnsfilaments as low as 8μm for stainless steel

Pure metals

They are produced using textile production technologies

They are referred to as: yarns

continuous fiber discontinuous fiber

Metal fibers (2)

Metal fibers (3)

metal + textile fibers

polyester + stainless steelpolyamide + stainless steel

yarn counts from Nm10/3 to Nm25/1

They are produced using textile production technologies

They are referred to as: yarns

Metallized fibers

- Polyamide-Silver combination- Polyamide yarns, textiles are coated with 99% pure silver- Each individual filament is completely coated with silver- Polyamide gives the yarn strength and elasticity, while soft, silver guarantees electrical conductivity

Metallized fibers

- High Tech polymers-metal combination- Coating with silver, copper or nichel - Each individual filament is completely coated with metal- very high conductivity and strenght

Carbon

- extremely thin fibers about 0.005–0.010 mm in diameter- produced from a precursor polymer- the precursor is first spun into filaments and after spinning, the polymer fibers are then heated to drive off non-carbon atoms (carbonization)- very low temperature coefficient of resistivity -0.0005 °C-1

Electricity in woven fabrics

Electricity in woven fabrics

Electricity in knitted fabrics

Electricity in knitted fabrics

Surface Resistancethe ratio of a DC voltage to the current, Is flowing between two electrodes of specified configuration that are in contact with the same side of a material under test

this relation depends on the type of material and, for non homogeneus fabrics, even from the orientation of the specimen. It is measured in Ohm per square

Resistive Sensor

resistive sensor: a converter that measures a physical quantity and converts it into a variation of electrical resistance

∆p => ∆r

this relation depends on the type of sensor

Classification of sensors

physical quantity: gas pressure, temperature, strain, mechanical pressure, humidity..

output: resistive, capacitive, inductive, piezo

digital (switches) – output 0 or 1 analog – output is a level

textile sensors are able to measure

- mechanical pressure

- strain ?

- movement (potentiometer)

- temperature

Textile Switch

• Knitted three-layered fabric, two conductive layers with a non-conductive layer in between

• If pressed, the conductive layers touch allowing current flow

• Materials: acrylic yarn, stainless steel

Pressure sensitive fabricCharacteristics

Activation force 3.6 Kg per 50 mm diameter

• More then 1.000.000 cycles• For a 15 cm x 20 cm switch

resistance when pressed: around 200 Ohm, open circuit when non pressed

Pressure sensitive fabricsInnovative aspects

• No need of further production steps

• Low cost

• Transpiring

• Semi-transparent

• Flexible

• Different activating pressures

• Matrix switches

• Large area switches (50 cm x 50 cm)

• Skin compatible materials

textile push button electrical behaviour

theoretical behaviour

real behaviour

textile push button:

digital

analog

Rtot

= Ru + R

c+ R

l ≈ C

Rtot

= Ru + R

c+ R

l ≠ C

Piezoresistive materials

a material that changes its electrical resistance with pressure

∆p => ∆r

- carbon- polypyrrole

Analog press sensor

sensitive layer

conductive side

conductive side

Matrix sensors

strain sensorsGauge factor (GF) or strain factor of a strain gauge is the ratio of relative change in electrical resistance to the mechanical strain ε, which is the relative change in length.

A high Gauge factor (GF) means that for a small mechanical strain ε, we will measure a big variation of R

Textile strain sensors can work in a limited range of strain

textile potentiometer

potentiometer = variable resistorcan be used for controlling sound or light level,

changing the frequency of a flashing LED

textile potentiometer electrical behaviour

theoretical behaviour real behaviour

light emitting textiles

Light emitting fabricsInnovative aspects

• No need of further production steps

• Low cost• Transpiring• Flexible • Large area (fabrics up to 100

cm width) • Skin compatible materials

EL wire

Courtesy of Lytec

Courtesy of Lytec

Characteristics

Extremely low consumption (100 mW - 1.6 W per m)

Flexibility

Possibility of fabrics with high density

(1 fiber per cm, weft)

High intensity of light (70-100 cd/m2)

P = V I = R I2

•

textile perfboard

knitting textile technologies

warp knittingweft knitting

knitting textile technologies

warp knitting

weft knitting

knitting textile technologies

weft knitting is the most versatile technology for 3D textiles and textile sensors

thank you!

Riccardo Marchesi

rmarchesi@plugandwear.com

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the teaching material is intended for personal use of the course participants and cannot be duplicated or disclosed for other purposes