A. Introduction
Clothing is one of our 3 basis needs. They not only protect us, but also have an aesthetic appeal and also are culturally important. However in recent years with the advancement of technologies, textile material is not confined to clothing anymore. With the introduction of smart textile the textile materials have turned to be more active where it can sense and react to environmental conditions or stimuli from, for example, mechanical, thermal, chemical, electrical, or magnetic sources [1].
The fundamental components in any smart textile are sensors and actuators. Interconnections, power supply and control units are also needed to complete the system. These components must all be integrated into textiles while still retaining the usual tactile flexible and comfortable properties which one expects from a textile [2]. For this the imperative item is electricity conducting textile materials for interconnection of different electrical or electronic components.
Metals like Copper, Silver, Aluminum, etc. are known to be electricity conductors, since they have free electron(s) which helps them in conducting electricity. Natural textile material inherently doesn’t conduct electricity since they are animal body hairs or cellulosic materials and doesn’t contain free electrons. Even majority of synthetic and regenerated fibres are non-conductors and hence used for resistive and capacitive applications. Many synthetic fibres of resistivity range 105W/cm2 are used for electromagnetic shielding applications [3], capacitive [4] and insulating applications. Textile fibres are however hydrophobic and its electrical properties changes with RH%, amount of moisture absorbed (Shown in Fig 1.), and temperature [5]. In spite of this the electrical properties even at favorable conditions are not suitable enough to be utilized for electricity conducting applications in e-textile hence metals are incorporated within the textile materials by various processes to obtain variety of applications in e-textiles.
Fig. 1: Log conductance
(C, Siemen) vs. Regain (%) for (a) cellulosic material [6], (b) Wool and silk
[7]
The production of
conductive materials can be traced way back. However the literature shows
patents of conductive yarns production from early 19th Century [8].
B.1.
Underwood’s technique of metal ribbon formation [8]
It is the process most commonly used
in industry. Here metals like silver, gold, copper, aluminium is extruded and
deposited onto a cold moving substrate to ensure fast cooling shown in Fig.
2(a). With this technique very fine
yarns suitable for knitting and spinning can be produced.
B.2.
Conductive core spinning [8]
In this technique a filament is twisted
around an existing yarn. The metallic filament is fed in a comparatively higher
tension between two strands of fibres. Being in higher tension, when relaxed it
twists with the two stands of yarn, and a pair of frictional rollers moving in
same direction helps in creating a core-sheath structure(Fig. 2(b)). This
technique is used for production of coarse count yarns.
B.3.
Commingled warp spinning [8]
This is a core
spinning yarn (Fig 2(c)), where the core is mainly drafted sliver with false
twist, and conductive yarn wrapped helically over it giving the yarn stability.
The yarns produced has high strength, good aberasive properties, wash wear and
perspiration resistant properties. However these yarns are fragile and brittle and
cannot conduct high electricity.
B.4.
Laminated/Coated conductive yarns [8]
In this spinning the substrate is
unwound from a spool and is passed through a tank containing liquid metals. The
dipping is precisely controlled to ensure even disposition of metal on the
surface. The dipped substrate is then heated in a heating chamber followed by
winding. The solution contains molten metals or carbon conductive halogens
(Fig. 2(d)).
B.5.
Bi component and multicomponent spinning [8]
In this technique thermoplastics are used where it
is melt spun with two or more component of conductive molten metals. During
extrusion the type of metal, shape of extruder and cooling effect determines
the final yarn shown in fig 2(e). Generally carbon nanotubes and graphene is
used for molten conductive part.
These types of yarns are very
robust, and their characteristic functions, such as stress-strain behavior, low
shrinkage, high modulus, good electrical conductivity, toughness, and solvent
resistance, can be tailored. Knittable yarns suitable for strain sensing and other smart
textile applications can best be produced via this technology. However, yarns
produced using this technology is not yet available in commercial markets.
B.6.
Extrusion coating spinning [8]
In this method a sandwitch is obtained where the conductive
metal sheet is in the middle and on both the side fibre sheets and wound onto
the bobbin. The laminated sheet is cut are then slit into filaments and spun
into yarns (Fig. 2(f)).
Fig. 2: Methods for
production (a) Underwood’s technique, (b) Core spinning, (c) Commingled
spinning, (d) Dip Coating, (e) Filament Matrixes, (f) Extrusion coating method
B.7.
Hybrid Ring spinning [9]
This a new technology, where the conductive yarns (Carbon
black and ethanol solution) is sprinkeled onto the sliver or roveing in
drafting zone for even diposition of the conductive material. With this
technique conductive yarn can be produced with the help of ring spinning system
with proper optimization done in the literature [9].
B.8.
Other conductive yarn producing methods
Several methods have been proposed, patented and developed in
the recent century for this technology. Blending in different contentrations of
conductive yarns in fibre stage is one such alternative but it is rarely used
due to uneven electrical conductance that might occur due to uneven blending
[8]. Plasma coating of conductive metals on yarn is another method used to
obtain highly conductive yarns [10]. Different coating metals and composits
like polypyrrole (PPy), polyaniline, and
polythiophene have been used for good conductance, environmental stability,
non-toxicity, etc. [11]. Polydoapamine is another self-polymerized substance
which has been extensively used for coating applications in several literatures
[11, 12]. Certain Carbon halogens like
graphene, carbon fibres, carbon nanotubes, have been used in several
literatures as a conductive yarns for superconductive, super capacitive applications
[8, 13]. These carbon halogens have also been doped onto fibres, fabrics and
yarns surfaces for higher conductance [14]. Silver and nano spun (generally
electrospun) Silver is also extensively recently for preparation of conducting
yarns, as microelectrodes, also to achieve anti-microbial effects on textile
[8]. Not only coated fibres, genetically
modified silk that conducts electricity has also been produced. Silkworm was
fed graphene and carbon nanotubes sprinkled on mulberry leaves, and the genetically
modified silk obtained was seen to be highly electricity conductive [15],
similarly genetical modifications of several other natural fibres are been
researched to obtain naturally conductive yarns.
B.9.
Other conductive textile producing methods
Several methods have been adapted for preparation of conductive textile in fabric, knitted and braided stages, coating and printing of textile with conductive inks [16] containing powdered metals are two of the most commonly used methods. Coating techniques including screen printing, ink-jet printing, electrodeposition, electroless plating, sputtering of thin films, vapor deposition and thermoset coatings have been used so far [17]. Doping of metals and carbon halogens onto fabric surfaces is also done [14]. It was seen it is most efficient and easy and cost effective to use conductive yarns than directly on fabric (Table 1). However in production of patterned electrodes conductive inks are preferred over yarns [18].
Table
1: Qualitative comparison of E-textile fabrication attributes [18]
E-textile Manufacturing Technique |
Machinery Cost |
Material Cost |
Process Complexity |
Resistance to wear |
Embroidery |
High |
Low |
High |
High |
Sewing |
Low |
Low |
Low |
High |
Weaving |
Low |
High |
High |
High |
Non-woven |
Low |
Low |
Low |
Low |
Knitting |
Low |
High |
High |
Low |
Spinning |
Low |
Low |
Low |
Low |
Breading |
Low |
Low |
Low |
High |
Coating |
High |
Low |
Low |
Low |
Printing |
High |
High |
Low |
Low |
According to manner of reaction, smart textile material can
be divided into passive smart, active smart and very smart material. Passive
smart materials can only sense the environmental conditions or stimuli; active
smart materials will sense and react to the conditions or stimuli; very smart
materials can sense, react and adapt themselves accordingly. An even higher
level of intelligence can be achieved from those intelligent materials and
structures capable of responding or activated to perform a function in a manual
or pre-programmed manner [19]. Of all these smart materials the key ingredient
is a conductive textile material and depending on the application the type of
sensors, actuators, and the conductive material varies as shown.
C.1.
Project Jacquard
Project Jacquard initially undertaken in 2016 by Google Inc. and Levi’s, is one of the Google’s Advanced Technology Projects. In this project conductive yarns are prepared and woven to produce interactive textile, that enables multitouch, navigation, communication and interaction with mobile phones and tablets using gesturing and touch sensing on textile surfaces.The project initially used on Levi’s Tucker Jackets is designed in such a way that it can be produced at a scale by standard textile manufacturing processes and can be dyed with any colour, ensuring comfort, breathability of the parent textile material remains intact. Depending on the design the sensing area can customised to be identifiable or invisible. The full manufacturing process of project jacquard is shown in Fig. 3. This technology can be used in clothing, furnitures, accessories, bags, toys, carpets, interior, automotive etc.[20]
Fig. 3: Project Jacquard manufacturing process
In 2020 this technology was used by Adidas, to produce Adidas GMR for EA SPORTS FIFA Mobile Games to give a interactive physical footballing and digital gameing. It has also been used by Saint Laurent in producing their luxuary range of backpacks Cit-e Backpack, that can control music, drop pins on go, take pictures with simple gesture [21]
C.2.
Military Applications
Georgia tech wearable motherboard(GTMW), initially developed
in 1996 by US Defence Advanced Project Research Agency is a wearable functional
clothing that alerts the medical triage unit when a soldier is shot or is in
need of medical attention. The particular apparel is designed to be light
weight, easy to wear and remove, breathable and durable for 120 combat days
that has the ability to withstand repeated flexure and aberation. The GTMW
contains sensors connected with a PSM( Personal Status Monitor) which senses
and informs the medical unit about the health condition of the particular
soldier. This technology though has been designed for soldiers however can also
be used in various sectors [19] , Table 2.
Table 2: Potential Application of GTMW [19]
Segment |
Application
Type |
Target
Customer Base |
Military |
Combat
Casualty Care |
Soldiers and
support personnel in battlefield
|
Civilian |
Medical
monitoring Patients |
Surgical
recovery, psychiatric care Senior citizens:
geriatric care, nursing homes Infants: SIDS
prevention Teaching
hospitals and medical research institutions |
Sports/performance
monitoring
|
Athletes,
individuals Scuba diving, mountaineering, hiking |
|
Space |
Space
Experiments |
Astronauts |
Specialized |
Hazardous
Applications |
Mining, Mass
Transportation |
Public Safety |
Fire
Fighting/ Law enforcement |
Firefighters
police |
Universal |
Wearable
mobile infrastructure |
All Information
Processing Applications |
For the army e-textile have also been used for locating
soldiers, communication purposes, monitoring environmental conditions, for
detecting infrared signals, decoding different audios signals of enemies, for
surveillance purposes infrared camera, laser range finder has also been
proposed. Even in certain camouflage applications e-textiles has been used [22]
C.3.
Medical Applications
Most of the Existing wearable technologies are based on
physical sensors and used for assessing different body parameters and for
diagonistics applications. The major monitoring specifications are given in
Table 3.
Table 3: Physiological signals
that may be measured using textile-based sensors [23, 24]
Physiological
measurement |
Textile-integrated
sensors |
Signal
source |
Typical
sensor placement |
Breathing patterns |
Piezoresistive
stretch sensors, inductive plethysmography, impedance plethysmography,
optical fibres |
Expansion
and contraction of ribcage during breathing |
Thoracic-
abdominal region |
Heart activity |
Woven/Knitted
electrodes |
Electrical
activity of heart |
Thoracic
region |
Muscle activity |
Woven/Knitted
electrodes |
Electrical
activity of muscles |
Skin
surface overlying muscle |
Blood oxygen saturation |
Optical
sensing components, plastic optical fibres |
Light
absorption of hemoglobin in blood |
Region
with good blood perfusion |
Blood pressure |
Features
of the photoplethysmography signal |
Arterial
pressure pulsations |
Finger,
wrist and earlobe |
Body movement posture |
Piezoresistive
strain/ pressure sensors, accelerometers, gyroscopes, optical fibre sensors |
Body
kinematics |
Dependent
on motion to be analyzed |
Electro dermal activity |
Woven
electrodes |
Skin
electric conductivity |
Fingertips |
Composition of body fluids |
Electrochemical
sensors, colorimetric pH fabric |
Composition
of sweat, saliva, urine |
Fluidic
sampling system necessary |
Body Temperature |
Thin
film flexible sensors, thermocouples, RTDs |
Heat
generated from the body |
Depending
on the part of body |
Adaptable textile antennas, smart clothing, smart bras
have also been proposed in the literature for detection of breast cancer, where
an electric current goes into the body detecting the different electromagnetic
conduction between tissues thus differentiating tumor tissue from a healthy
one. [25,26].
Not only sensing medical textile with drug releasing
applications have also been using sensors [27], smart wound detection by
textile garment with sensing and localization application has also been
designed using conductive textiles [28].
C.4.
Fashion and Accessories
The recent developments and commercialization of wearable computer
technologies have brought about several changes in the fashion industries. The
textile and fashion has not only embressed this change, but also changed along
with it. Major main stream fashion accessories like wrist watches, bracelets,
nechlaces had digital features addition [29]. Even certain fashion designers
have used the E-textile in their collections [30].
C.4.1. Wearable Solar
Pauline
van Dongen and Christiaan Holland in 2013 initially designed the Wearable Solar
collection. This is a fusion of technology and fashion, where technology is
used to make light weight wired garments that enable the wearer to charge up
smartphone upto 50% if the wearer stands in Sun for 1 hour. Fig 4(a)
C.4.2. Cute Circuit
Internationally
known fashion house Cute Circuit have been a global leader in implementing
technology into wearable technology, since 2004. They have had many ground
breaking fashion ideas to fashion by using microelectronics for value addition
to fabric; they even have a fabulous international celebrity fan base such as
Nicole Scherzinger and Katy Perry. Their products are Oeko Tex certified, i.e.
completely safe for the use of common people. Fig 4(b)
C.4.3. Rainbow Winters
Rainbow Winters is a
clothing lines designed by Amy Winters. They are a range of interactive
clothing which reacts to different stimuli. Majority of the dresses are made of
holographic leather, which illuminated when the surrounding sounds gets louder;
Winters describes it as “visual music”.
Even her bathing suit line reacts to light, where purple dots appears
when exposed to sun With the advancement of smart and interactive textile, the
fashion trends have changed. Similarly fashion designers have also adapted to
the technology and they are bringing change in their business model and designs
[30, 31]. Fig 4(c)
Fig 4: Different
Fashion and smart textile fusions, (a) Wearable Solar garment, (b) Cute Circuit
sound shirt, (c) Rainbow Winters garment
C.5.
Other Applications
From
the use of classical electronic devices like wires, LEDs, batteries into
textile materials it has evolved considerably. However the application of
e-textile is still limited due to the fact the production of these has not yet
become main stream. Apart from medical, fashion, millitary applications
production of green energy is another aspect. Production of solar energy (Solar
Textiles) from textile has been used for
decades. Production of energy from human limb movement [32] has opened a
new direction in green energy production.
Fig.
5: Schematic illustration of Microbial Fuel Cell operating Principle [33]
Microbial
fuel cells which generated energy from waste water or any biodegradable
compounds is a new green energy that has been researched in recent years even
its integration into textiles has been done [33]. Its operation is shown in Fig. 5 . Garments,
skin mountable batteries has been designed which can generate voltage of 0.5V,
200μA/cm2 cuttent density depending on the type of bacteria from
human sweat [34]. Similar green energy from different sources is being intensively researched and e-textile has
opened a new route for this developments.
D. Demands in Present
and Future Applications
A
market survey conducted by Grand View Research shows the Market size of smart
textiles for e-textiles is expected to reach $5.55 Billion by 2025, with a CAGR
of 30.4% [35]. It has been revealed the consumption of Passive, Active and Very
smart e-textile has significantly increased from 2011-2015 to 2015-2020 and is
expected to rise in the period 2020-2025. One of the major barriers is
naturally obtained textile materials don’t conduct electricity as a result the
production cost of these materials are significantly high shown in Fig. 6. Hence compared to any textile integrated
material, normal metal and alloys provide far better conductance in a lesser
cost as a result it is a shortcoming. Carbon fibres in recent times have gained
significance and might be very useful in the future.
In
current pandemic situation where thermal scanning is an important aspect,
temperature sensing integrated textile can be very useful for detecting fever
of any individual.
Fig.
6: Electrical resistivity Vs. Cost of the e-textile materials [25]
E.
Conclusion
The advancement of smart textile has seen a growth in
consumption of e-textiles. With new applications now e-textiles is not only
limited to high end fashion, it has found its ways into medical, military,
automobiles, green energy production fields. With a current growing market and
with the change in fashion trends, the day is not very far when the e-textiles
will find its way into wardrobe of common people.
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4 Comments
Informative article. Very well written!!🙌
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ReplyDeleteOverall good and very informative .......
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