Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
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
for text and images ©All rights reserved
the teaching material is intended for personal use of the course participants and cannot be duplicated or disclosed for other purposes