Sungmin Kim

SEOUL NATIONAL UNIVERSITY

Smart Garment Design

3. Materials

Conductive Material Conductive Textile Material In the early stage...

Manufactured primarily for medical and industrial purposes

– Antimicrobial, antistatic, EMF (electromagnetic field) shielding purpose

Not sold in smaller quantities

Aesthetic aspects have not been well considered

Nowadays...

Available for consumer products

– Gloves for touch screen devices

– Sensors for heart rate or brain wave

– Conductive flexible electrodes

Wide range of aesthetic options are available

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Conductive Fiber Metal Fiber

Characteristics

Powerful raw material that can be used in a variety of projects

Soft and light weight

It can be spun, felted, and more

Example

Beknix, e-Thread

– Stainless multifilament fiber

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Stainless steel fiber

Conductive Fiber Metallized Fiber

Characteristics

Fiber coated with metal

Example

Organza

– Silk filament wrapped with thin gold foil

AmberStrandQ (Sycom)

– PBO (Polybenzoxazole) fiber wrapped with metal

ContaX (Nobel Biometerial)

– Fiber containing silver

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Embroidered Antenna

Conductive Fiber Fiber from Inherently Conductive Polymer

Conductive Polymer

Studied since 1977

Won Nobel prize for Heeger, MacDiarmid, Shirakawa (2000)

Example

Polyaniline (PANI)

Polypyrrole

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Conductive Fiber Conductive Carbon Nano Tube Fiber Characteristics

High tenacity

High conductivity

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Conductive Yarn Cotton-Wrapped Nichrome Yarn Structure

Combed cotton yarn wrap the nichrome wire

Wrapping is carried out by braiding technique

Characteristics

Coarser count yarn would be better

– Provides better wrapping with high surface area

– Better heat dissipation for preventing thermal shock

Use

Heating fabric

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BraidedYarn

Conductive Yarn Copper Core Yarn Structure

Core-sheath type yarn

Copper core filament is wrapped by cotton fiber by friction spinning

Use

Electrically Conductive fabric

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Conductive Yarn Copper Core Yarn Industrial Importance

Used to develop sensor wears and signal-transferring applications

– Defense, medical, and technical textiles

Can be woven and knit into special fabrics

– Antielectrostatic fabric

– Electrostatic dissipating fabric

– Telecommunication textile device

– Electromagnetic shielding fabric

– Body temperature control jacket

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Conductive Yarn Optical Core Conductive POF Yarn Structure

POF (plastic optical fiber) is wrapped by cotton sliver using friction spinning system

Use

Communication fabric

Illuminated fabric

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Conductive Yarn Working with Conductive Yarn

Hand Sewing

Needle with a larger eye is needed

Secure knot is needed

– Conductive yarn can be a bit slippery

– Fabric glue is sometimes required

Machine Sewing

Use the conductive yarn in the bobbin

Prevention of Shorts

Most conductive yarns are uninsulated

Keep the circuits neat, trim, and organized

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Conductive Yarn Properties of Conductive Yarn Thickness

Determines the type of needle and the availability for sewing machine

The more plies, the less resistive the yarn will be

Resistance

One of the most important factors to consider when choosing a conductive yarn

Affects how they can be used in a circuit

Material

Different materials have different conductivity and physical properties

Insulation

Insulated conductive yarn does exists

However, there are no insulated conductive yarn available in small quantities

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Conductive Fabric Characteristics of Conductive Fabric Lower Resistance than Conductive Yarn

Do a better job in circuits with higher-current demands

Working with Conductive Fabric Sewing

Conductive fabric can be sewn just like any other fabric– Quilting and applique techniques can be used

Prevention of Shorts

Yarns from frayed piece can wander and inadvertently

create shorts

Can be mitigated through hemming, serging, or other traditional

sewing techniques

Iron-on Adhesive

Conductive fabric can be purchased with iron-on adhesive already applied

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Conductive Fabric Properties of Conductive Fabric Substrate

Non-conductive base layer affect the care and comfort of the final product

– Nylon, polyester,...

Weight and Thickness

Important to consider in the context of the product

– Lightweight fabric for light t-shirt

Stretch

A stretch fabric can be helpful for a garment that needs to shape-shift or bend frequently

Surface Resistance

Many conductive fabrics have an extremely low surface resistance

Color

Most fabrics are in silver or copper

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Other Conductive Material Conductive Felt How to Make

Combining conductive fiber or conductive wool with sheep's wool

Use

Tactically pleasing variable resistor or electronic switch

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Other Conductive Material Conductive Ribbon Type

Single conductor type

Multiple conductor type

– Uninsulated– Insulated

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Other Conductive Material Conductive Velcro Use

Act as a secure and sensible electronic switch for clothing

Conductive Paint Use

Paint, draw, or silk screen circuits

Works best on a nonporous substrate

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Textile based Sensors Textile Sensors Definition

A sensor in which fiber itself acts as a sensor

Types

Fiber Type

– Optical Fiber» Trouble-free transfer of information even at a high electric field» Can be used to temperature measurement by monitoring the refractive index of cladding» Can be used to pressure measurement using micro bending effect

Yarn Type

– Used to detect the stress caused due to the influence of mechanical abrasion or UV

2D or 3D Fabric Type

– Bind multiple sensors to create a single sensor module– Fabricated by weaving or knitting process.

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Textile based Sensors Development Stages

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Material selection Select suitable material for the delivery of signal energy

Measurement parameter decision

Determine the physical values to be measured as signal and develop

Prototype making Make a prototype using sewing, knitting, weaving, coating, embroidery

Connectivity test Solves the problem for the connection of the sensor and other electronic components

Data analysis and evaluation Check the characteristics of the sensor by measuring the linearity of data, for example

Range determination Check the characteristics of the sensor by measuring the linearity of data, for example

Textile based Sensors Examples Capacitive Sensor

Principle

– Two opposing electrodes are separated by an insulating material

– When voltage is applied to the circuit, the electrode is charged to positive and negative

– The insulator prevent the electron current and an electric field is generated between electrodes

– The energy storage capacity is dependent on the distance between the electrodes

– Therefore, flexible textile electrodes can convert the change in pressure into electrical signals

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Textile based Sensors Examples

Temperature Sensor

Can be made in various structures unlike electronic sensors

– Can cover a large area and measure the distribution of temperature over a large area

– Can measure the temperature of skin close to the body

– Can be used for physiological and medical monitoring

Prepared by coating, weaving, knitting, embroidery, printing, etc.

– Operates on the principle of the thermocouple, resistance, and conductivity

Special fiber optic type sensor

– Implementation FBG (Fiber Brag Grating) and the functional coating

– A single fiber can measure the temperature distribution over a large area

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Textile based Sensors Examples

Moisture Sensor

The amount of water vapor in the air is very important in many manufacturing processes

– Monitoring and control of moisture is critical in the medical, industrial and domestic applications

Sometimes the measurement over a wide area is necessary

– A fabric type sensor may be most appropriate

Pressure Mapping Sensor

A sensor for quantifying the pressure between two surfaces

– Based on a capacitive sensing element or piezoresistive element

Applied to mat or socks to read the pressure acting on thigh, hips, feet, etc.

Fabric made of pressure-sensitive filament may sense the pressure in all parts of the body

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Textile based Sensors Examples Pressure Mapping Sensor

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Smart socks (Alpha-Fit)

Textile based Sensors Examples Pressure Mapping Sensor

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Project Jacquard (Google)

Textile based Display Color Changing Interactive Fabric Judit Eszter Karpati (Hungary, 2014)

Interactive fabric using computer programming, engineering and electronic devices

Slow moving textile ‘displays’ to show the content, which react to environmental changes

It changes color and pattern when heated up or pressed

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Textile based Battery Textile Battery Volvo (Sweden, 2013)

Turn body panels into batteries

Same output with 50% reduction in battery weight

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Textile based Battery Textile Battery KAIST (2013)

Polyester fiber based battery

Flexible, foldable, rechargeable (solar powered)

Can have various form factors

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Flexible Solar Cell Solar Cell Importance

Infinite source of energy prior to the nuclear fusion technology

Most renewable energy device cannot repay the energy to make during their lifetime

– Hydro, wind, etc.

Photovoltaic (Solar) cell generates more energy than they consumed

– Alsema (2009), Lind (2015)

Current Problems

Solar cells are put between glass/polycarbonate plates due to weak nature

– Glass is fragile and polycarbonate glass is heavy

– Durable and lightweight material is needed

Application of thin flexible plastic or metal films has been studied

– Lighter than polycarbonate glass but still fragile

Textile-based solar cell has many advantages

– Light, durable, flexible, ...

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Flexible Solar Cell Textile based Solar Cell Using Organic Photovoltaic Fiber (Bedeloglu, 2010)

Mass production of polymer film attached fabric is possible

– Solar cell film can be attached to fabric but it can be damaged by the bending of fabric

Direct deposition of solar cell on the fabric is most desirable

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Cover Film

Transparent conducting oxide

Silicon film

Metal film

Organic conductor

Fabric

Flexible Solar Cell Textile based Solar Cell Solar Cell Fiber (Japan)

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SphericalSolar Cell

1.2mm

Flexible Solar Cell Future of Textile based Solar Cell

Most Suitable Power Sources

Fashion products

– Conceptual products of solar powered jackets and backpacks have been made

– Most of them using the costly method of the integration of conventional silicone based solar cells

Low-energy electronic devices

– Personal health status monitoring devices

– Sensors for wearable devices

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Flexible Solar Cell Future of Textile based Solar Cell Wide Coverage

Wide area textile based solar cell can be used for shade or canopy

– Solar tent that can supply power to various electronic equipment (PowerFilm Solar, Inc., USA)– Personal solar panel for a soldier with radio communication, GPS, laser rangefinder, etc.

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Energy Harvesting Material Piezoelectric Material

Piezoelectricity

One of the most important discoveries in 19th century

– Pressure applied to a material is converted in to electric energy

Natural piezoelectric material

– Quartz, bone, tendons, enamel, dentin, etc.

Synthetic piezoelectric material

– Some ceramic and polymer materials show piezo electricity

– Piezopolymers have some advantages over Piezoceramics such as piezoelectric performance or flexibility

– Polyvinyliden fluoride (PVDF) is knows to be the most suitable piezoelectric material

– Nanowire and Carbon nano tubes are also suitable for piezoelectric applications

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Energy Harvesting Material Applications of Textile-based Piezoelectric Material Human Powered Wearable Devices

Modern electronic devices require only a few mW of power

Human motion would be sufficient for providing power to those devices (Stamer, 1996)

– Electricity from the change in the chest circumference due to respiration (Zieba (2010), Wang (2012))

– Driving a pace maker using blood pressure and heart beat

– Electricity from heel-attached piezoelectric material (Kymissis, 1998)

– Piezoelectric energy harvesting device for finger joints and elbow (Yang, 2012)

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Energy Harvesting Material Applications of Textile-based Piezoelectric Material

Military Applications

Light weight energy devices is required

Even flexible solar cells cannot be used without sun

– Piezoelectric energy harvesting can be continued in the dark

Medical Applications

Uninterrupted power supply is required

– ECG (electrocardiogram), sleep monitoring, breast cancer detection underwear, etc.

– Energy harvesting is the most desirable solution considering the weight of battery

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Energy Harvesting Material From Body Temperature Human body generates a few mW of heat energy

Micro heat-electricity converter can harvest those energy

– Usually made by expensive bismuth telluride semi conductors and unsuitable for wearable devices

– Silicon based flexible chip can be considered to be an alternative material

Heat-Electricity converter chip should be integrated into fabric itself

– To obtain maximum temperature difference between inner and outer surface of the chip

– One surface faces the body and the other surface faces the outer air

– Generates about 1.6µW/cm2 of electricity, which is sufficient to power a wrist watch

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More Issues Laser-Cut Fabric PCB Fabrication Process

A heat activated adhesive is attached to a conductive fabric and covered with a paper Place this fabric, paper side up, into a laser cutter where a circuit pattern is etched

– The adhesive and paper backing are cut, but the fabric is only scored

Once the circuit is cut, the backing paper is removed from underneath the circuit The circuit is then carefully aligned on its fabric substrate and ironed into place

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e-Textile Component Laser Cut Fabric PCB Solder Joint Treatment

Fabric PCBs are subject to abuses such as the twisting, folding and stretching of cloth

Solder joint must be covered with an inflexible coating to prevent possible breakage

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e-Textile Component Insulation Importance

Electrical traces may come in contact with one another as a fabric flexes

Traces on textiles must be insulated and protected to prevent short circuits

The insulation must preserve the qualities of the textile - soft, flexible, and stretchy

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Couching Embroidery Iron-on Patch Puffy Fabric Paint

e-Textile Component Flexible-Stretchable Electronics Fundamental requirements for electronics to be integrated into clothing

Many promising demonstrations have surfaced

– There is no real ‘go-to’ solution up to now

Viable Solution

Using a zig-zag stitch for conductive lines between electronic components sewn onto textiles

– The robustness of this technique is not that great – Additional layers of fabric is needed for wear and wash protection

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e-Textile Component String Battery LG Chem

Li-Ion battery in string form just a few millimeter thick

Bendable and can even be knotted without compromising it’s battery function

A reasonable power supply completely integrated in garments and bags.

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e-Textile Component Flexible Battery Jenax J-Flex (2019, Korea)

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