Wearable Textile Antennas

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Wearable textile antennasJung-Sim Roh a , Yong-Seung Chi b & Tae Jin Kang ca Intelligent Textile System Research Centreb Fashion Textile Centrec Department of Materials Science and Engineering, Seoul National University, Seoul,151-744, Republic of Korea

Available online: 04 Oct 2010

To cite this article: Jung-Sim Roh, Yong-Seung Chi & Tae Jin Kang (2010): Wearable textile antennas, International Journal ofFashion Design, Technology and Education, 3:3, 135-153

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REVIEW ARTICLE

Wearable textile antennas

Jung-Sim Roha, Yong-Seung Chib and Tae Jin Kanga,b,c*

aIntelligent Textile System Research Centre; bFashion Textile Centre; cDepartment of Materials Science and Engineering,Seoul National University, Seoul 151-744, Republic of Korea

(Received 14 July 2010; final version received 20 September 2010)

Owing to the rapid progress in fabrication technologies of conductive fibrous materials and the increasing demandfor wireless communications in smart clothing systems, the potential application of wearable textile antennas in thisfield continues to increase. This article reviews a variety of wearable textile antennas in order to provide backgroundinformation and application ideas for designing such antennas. The various materials used in the construction ofwearable textile antennas, their fabrication methods, as well as the antenna types and their application fields aresummarised. Owing to the high conductivity of metals, various metal composite yarns (MCYs) and fabrics havebeen used in the production of textile antennas. For inductively coupled near-field communication within smartclothing systems, woven or embroidered multiturn loop antennas are suggested. For far-field communication, avariety of broadband textile antennas were developed to counterbalance the detuning caused by the presence of ahuman body. Embroidered-folded dipole array antennas, metal-coated fabric patched bowtie and spiral antennas,a microstrip patch antenna array and a coplanar antenna made of metal-coated fabric patches and a ground plane,are the antennas that cover a broad spectrum and thus are capable of operating on the body.

Keywords: wearable textile antennas; embroidered antenna; conductive fabric patch antenna; printed textile antenna;broadband textile antennas; textile antenna arrays

1. Introduction

As fabrication technologies for conductive fibrousmaterials have rapidly progressed in recent years, thedoor to producing flexible structures for wearableelectrical and electronic systems has opened even wider.In this context, conventional textile industries haveemployed new strategies to support the innovation ofsmart products and enhance their functions. As a result,the production of smart textile systems is now becominga reality based on the successful convergence ofconventional textile-producing technology with otherbranches of science such as material science, sensor andactuator technology, data processing and communicat-ing technology, electronics and electromagnetic engi-neering, artificial intelligence, bio-technology, etc.Currently, reduced-sized electronic devices or electricalcircuit components are being built on or incorporatedinto textile-based structures using available technologies.

As the demand for wearable smart textile systemscontinues to increase, the interest in body-wornantennas is growing, thanks to the expanding wirelessapplications for smart interactive textile systems. Asclothing provides sufficient area to place antennas,which usually require a relatively large space, andtextile antennas ensure wearing comfort owing to theirflexibility, conformability and lightness, much research

on smart textile systems has been focused on wearabletextile antennas. The potential applications of wear-able textile antennas are diverse, ranging from medicalapplications to health, sports, military and spaceapplications (Jung et al. 2003, Dobbins et al. 2006,Locher et al. 2006, Salonen and Rahmat-Samii 2007,Visser and Reniers 2007, Hertleer et al. 2009, Kennedyet al. 2009, Vallozzi et al. 2009, Zhu and Langley2009a).

Early wearable antennas were non-fibrous stiffconductive structures constructed on a textile sub-strate, such as the inverted-F shape antenna bySalonen et al. (2000) and Massey (2001), rectangularpatches of copper foils by Tanaka and Jang (2003),and linear patches of copper foil tape on fleece fabricby Kellomaki et al. (2006). Recently, by using variousconductive fibrous materials, textile antennas made ofpurely conductive fibrous materials have been success-fully integrated into clothing. However, many designconstraints follow the integration of antennas intoclothing due to the physical inhomogeneity of textilematerials, the proximity of a lossy human body orother irregular ground conditions, and differentpolarisation due to body movements.

Therefore, by reviewing a variety of wearabletextile antennas, including the conductive fibrous

*Corresponding author. Email: [email protected]

International Journal of Fashion Design, Technology and Education

Vol. 3, No. 3, November 2010, 135–153

ISSN 1754-3266 print/ISSN 1754-3274 online

� 2010 Taylor & Francis

DOI: 10.1080/17543266.2010.521194

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materials used, their fabrication methods, as well as theantenna types and their application fields, the im-portant points to be considered when designingwearable textile antennas are summarised in thisarticle.

2. Materials and fabrication methods

Conductive materials used for producing textileantennas include metallic yarns, yarns made fromconductive polymers, polymer yarns containing highlevels of conducting particles, such as carbon or silver,and conducting thin inorganic films (Ghosh et al.2006). Textile antennas can be made either by weaving,embroidering, laminating or printing. The level ofconductivity and the textile-processibility of the con-ductive materials are the most important aspects to beconsidered in producing textile antennas. In manycases, conductive composite fabrics that have a thinlayer of metal coating on a non-conductive fabric baseor those containing metal filaments were the choice forthe production of radio frequency (RF) engineeredtextiles owing to the characteristic physical propertiesof metals, i.e. their high conductivity, ductility andmalleability.

2.1. Weaving

Metal composite fabrics containing superfine metalfilaments or metal-coated polymer yarns opened thedoor to a new generation of multifunctional andinteractive textiles by replacing traditional metal wiretechnology (Roh et al. 2009). Superfine metal filamentsof silver, copper, or Ag-coated copper with diametersin the range of 20–60 mm have been used to formwoven electrical circuits. Metal-coated polymer yarnshave also been woven into textile materials to be usedas antennas, textile electronic buses or as flexibleelectronic boards. But unlike metal filaments, metal-coated polymer yarns require additional galvanicdeposition of metal to approach skin depth and supplythe required conductivity to such structures. Skindepth is the depth below the surface of the conductorat which the current is 1/e times the current at thesurface. For example, an Ag-coated polyamide yarn isable to achieve a resistance as low as 14 O/m when Au-plated (ø: 1*2 mm) (Kallmayer et al. 2003, Gimpelet al. 2004).

2.1.1. Jacquard weaving with non-insulated conductiveyarns

When using non-insulated conductive yarns, jacquardweaving has been used to produce multi-layer struc-tures in order to prevent short circuits due to crossing

conducting yarns (Figure 1). Conducting warp yarns inthe upper layer and conducting weft yarns in the lowerlayer are only in contact at the corners to form anantenna coil and are insulated by an intermediate non-conducting textile layer (Gimpel et al. 2004). Thismethod requires bonding with conducting adhesive atevery contact point of the warp and weft conductiveyarns in the three-layered structure. This procedure iscomplicated and time-consuming.

2.1.2. Weaving with insulated conductive yarns

With insulated conductive yarns, basic weaving andspecial fusing technologies have been used to formdesired circuits (Figure 2(a)) (Jung et al. 2003, Locherand Troster 2007). Figure 2(b) and (c) shows superfinemetal filaments embedded into plain woven fabrics.Figure 2(b) is PowerMatrix1 produced by SEFAR(Locher 2007), which is a hybrid fabric consisting ofinsulated Ag-coated copper monofilaments and poly-ester (PET) monofilament in both warp and weft. Theductile but weak metal filaments are able to maintaintheir conductivity without yarn breakage and defor-mation within the woven structure of PET due to thehigh strength and low elasticity of PET.

Roh et al. (2008, 2009) produced metal compositeyarns (MCYs) which can be woven into fabrics on acommercial automatic rapier loom. The MCYs con-sisted of superfine metal filaments, stainless steel (Ø:35 mm), Ag-coated copper (Ø: 40 mm), or polyester-imide-coated Ag-coated copper (ØCu: 40 mm, Øtotal:47 mm) and PET multifilaments. The PET wasincorporated to prevent the metal filaments fromextending and breaking during the weaving process.With a PET filament as a core, a metal filamentwrapped the core PET filament in the Z-direction with

Figure 1. Three-layered structure of a woven coil with non-insulated conductive warp and weft of Au/Ag-coatedpolyamide yarns only in contact at the corners to form amulti-turn loop (Gimpel et al. 2004).

136 J.-S. Roh et al.

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500 TPM (twists per metre), and then another PETfilament wrapped the previous metal wrapped PETyarn in the S-direction with 500 TPM (Figure 2(c)).Metal composite fabrics could be easily constructedinserting MCYs in certain intervals as warp and weftto obtain different metal densities.

To bond the crossing warp and weft of polyester-imide-coated Ag-copper filaments, a laser beam wasused to remove the PET substrate and to skin thepolyesterimide-insulation coating from the Ag-copperfilament. For skinning, an Excimer laser XeCl (at308 nm) or Nd-YAG laser (at 355 nm) with pulseenergy 1.01 J/cm2, pulse rate 500 Hz, and pulse duration25 ns, was applied. The filaments were cut with a laserbeam using a higher fluence than that applied forskinning and the bare warp and weft metal filamentswere interconnected using a conductive adhesive. As thelast step, epoxy resin was deposited to encapsulate theconnection (Figure 3) (Kirstein 2005).

2.2. Embroidering of conductive yarns

Machine embroidering of conductive yarns on textilesubstrates is considered a very attractive approach toproduce textile-based circuits due to the freedom ofcircuit design and ease of fabrication (Ghosh et al.2006). Embroidering of conductive yarns can be widelyused for wire-line integration of electronic devices and

for the construction of various circuit componentssuch as inductor, capacitor and transmission lineelectrodes for sensing and antenna circuits for wirelesscommunications.

Figure 2. Woven fabrics with embedded insulated conductive yarns: (a) design of a woven coil using insulated metal filamentsby Infineon Technologies AG (Jung et al. 2003), (b) micrograph of a woven fabric of insulated copper wire of Powermatrix bySEFAR (Locher 2007), and (c) Metal composite fabric produced with MCY containing an Ag-copper filament by Roh (2010).

Figure 3. Bonding technologies of insulated copperfilaments: (a) laser skinning, (b) adhesive dispensing, (c)laser cutting and (d) epoxy protection (Kirstein 2005).

International Journal of Fashion Design, Technology and Education 137

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During high speed embroidering, the embroideryyarn, especially the needle yarn, is subjected to hightension, which adversely influences the quality of theyarn. Thus, to be used in machine embroidering, highmechanical properties are required of the yarn(Sundaresan et al. 1997, Costs Technical Services2007). Mallet and Du (1999) have measured the sewingforce of a sewing machine using a piezoelectric straingauge sensor. They reported that the sewing force was5.6 N at a sewing speed of 1000 rpm, and 6.1 N at 2000rpm on a 1 mm-thick substrate. Therefore, conductiveembroidery yarns should possess good mechanicalproperties to reduce the number of breaks and theamount of strain in order to maintain their conductiv-ity. High tensile strength and modulus are required forthese yarns, as well as a smooth surface for less frictionand uniform yarn diameter. These qualities willprevent yarn breakage during the embroidering pro-cess and shrinkage afterwards, providing uniformconductivity and dimensional stability of the resultingembroidered circuit. Up until now, three types ofconductive embroidery yarns (Roh et al. 2009) havebeen developed and used in the construction ofelectrical circuits, and the characteristics of these yarnsare listed in Table 1.

2.2.1. Embroidering of metal filament bundles

2.2.1.1. Plied yarn of stainless steel filaments.Commercially available plied bundles of stainlesssteel filament have been used in the construction ofembroidered circuits. Figure 4 shows a three-plied yarnof stainless steel (AISI 316L) filaments where thediameter of the monofilament is 12 mm, number offilaments is 275, and is twisted in the S direction with175 TPM (Bekinox 2006). Compared to copper,stainless steel has better mechanical properties. Butalthough the mechanical properties are better thancopper, the conductivity of this stainless steel yarn iscomparably lower, so its usage is limited to textilesensors or electrodes rather than RF engineeringapplications.

2.2.1.2. Stainless steel yarn with a copper core.Coosemans et al. (2006) used a stainless steel yarn (ø:19 mm) with a copper filament core (ø: 79 mm) andproduced an embroidered transponder antenna(Figure 15(b)). The resistance of this yarn was quitelow, 0.20 O/m, but due to the limited winding densityof the yarn, an antenna with the optimal number ofturns (N ¼ 33) could not be produced. AlthoughCoosemans et al. did not comment on themechanical properties and the yarn structure, it islikely that this yarn cannot be used for high-speed

computer numeric control (CNC) embroidering, dueto the plasticity of stainless steel and copper.

2.2.2. Plied yarn of metal-coated polymer filaments

A variety of metal-coated polymer yarns with tradenames such as X-static1, Agposs1 (Figure 5(a)),Shieldex1, Aracon1, AmberStrandTM (Figure 5(b)),etc. are available as conductive embroidery yarns. Theconsumer can choose among a variety of metal types,coating thicknesses and the number of filaments andstrands to meet individual requirements. Compared topure metal filaments, the flexibility, lightness andstrength of metal-coated polymer yarns make themmore similar to common textile materials. So despitetheir lower conductivity, these conductive yarns havebeen applied in flexible circuitry, electrical interconnec-tions, cables and bio-monitoring sensors (Linz et al.2005, Sosnowski 2007). Among these, Aracon1 andAmberStrandTM, where high-performance polymerfibres such as Kevlar1 (para-Aramid) and Zylon1

(PBO, Poly-phenylene benzobisoxazole) are used as thebase filament, can be directly soldered using a solderingiron (NASA 2007, Syscom Technology Inc. 2005)

Generally, metal-coated yarns have considerablyless-than-ideal conductivity and inhomogeneous struc-tures with shallow skin depth (Shaw et al. 2007). So, inorder to reduce the electrical resistance of a metal-coated yarn circuit to a desired level, current commer-cial metal-coated polymer yarns require additionalgalvanic deposition of metals to increase their skindepth. Another existing problem with metal-coatedpolymer yarns, especially those that are nylon-based, isthat they contract at temperatures over their glasstransition temperature. Thus, the resistivity of theinterconnection between the metal-coated polymeryarns and devices can be modified permanentlydepending on the environmental temperature (Simon2009). Moreover, the metal coating has poor durabilitydue to its low abrasion resistance.

2.2.3. Composite yarn consisting of metal filamentsand polymer filaments

As shown in Table 2, stainless steel filaments havebetter tensile properties than silver-coated copperfilaments; thus, it is easier to make MCYs usingstainless steel filaments than silver-coated copperfilaments. Post et al. (2000) reported a stainless steelcomposite embroidery yarn, VN 140 nyl/35 6 3,having a nylon core wrapped in three crossing super-fine stainless steel filaments. Unfortunately, the elec-trical resistance of this yarn was too high to match theconductivity of conventional printed circuits, and dueto the high rigidity and plasticity of the stainless steel


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Table

1.

Characteristics

ofcurrentlydeveloped

conductiveem

broideryyarns.

Yarn

type

Researchgroup

(tradename)

Yarn

specifications

Thickness(lineardensity)

Resistivity(O

/m)

Bundle

ofmetal

filaments

Plied

yarn

ofstainless

steelmulti-filaments

Bekinox1

VN

(12/

36

275/175S/316L)

(BEKAERT

2006)

Threeplies

ofstainless

steelfilaments

(12mm

6275f)

630mm

(760tex)

9.13

Stainless

steelyarnswith

acopper

core

Coosemanset

al.(2006)

Stainless

steelyarns(ø:19mm

)witha

copper

wirecore

yarn

(ø:79mm

),limited

circuitdesigns

–0.20

Metalfilament

composite

yarn

Stainless

steel/nylon

IBM,Post

etal.

(Bekinox1

VN

140nyl/356

3)(Post

etal.2000)

Nyloncore

wrapped

withthree

crossingstainless

steelfilaments,

suitable

aslower

yarn

forCNC

embroidery

–*1000

Ag-copper/polyester

Ohmatex,Bi-component

yarn

(Ohmatex2004a)

Polyester(240dtex/48f6

2)air

texturedyarn

withsilver-plated

copper

filament(40mm

:123

dtex6

2,63mm

:305dtex6

2)

400mm

(40mm

:72.6

tex,

63mm

:109tex)

7.75,3.25

Ag-copper/polyester

Rohet

al.(2009)

Threeplies

ofAg-copper

filament(40

mm)andpolyester(83dtex/36f),

suitable

asboth

upper

andlower

yarn

forCNC

embroidery

Upper

yarn:286mm

(59.8

tex),lower

yarn:

272mm

(59.0

tex)

3.89,3.88

Plied

yarn

ofmetal-

coatedpolymer

filaments

Silver

platednylon

FraunhoferIZ

M(Linz

2009)

Twoplies

ofShieldex

1117/17dtex

(23.4

tex)

350

Silver-coatedpolyester

MitsufujiTextile

Ind.

Co.,Ltd.(A

Gposs

1)

Threeplies

ofAg-coatedpolyester

filaments

455mm

(66.6

tex)

26.2

Metalplatedaramid

DuPont(A

racon1)

(Post

etal.2000)

Plied

yarn

ofsilver,nickel,copper,

gold

ortincladaramid

15mm

6(24f–200f)

*0.1

Silver-coatedPBO

AmberStrandTM

(Syscom

Technology

Inc.

2005)

Threeplies

ofAg-coatedPBO

104.3

tex

7.87


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filaments, this yarn will not be suitable for CNCembroidering.

Ohmatex (2004a) has developed a bi-componentyarn composed of two strands of silver-plated copperfilaments (40 mm or 63 mm) and polyester filaments(240d/48f 6 2) through an air texturing process tolock them together (Figure 6). The resistance andlinear density of the yarns with Ag-Copper 40 mm or63 mm were 7.75 O/m, 726 dtex and 3.25 O/m, 1090dtex, respectively. The producer has reported atheoretical probability of 63% that a break wouldnot reduce the conductive capacity of the yarn, andthus it is suitable for constructing an embroideredelectrode (Ohmatex 2004b). However, electricallyconductive embroidery yarns to be applied in RFengineering textile systems should possess the lowestpossible electrical resistance, embroidering processibil-ity without yarn breakage, and high durability tomaintain constant electrical conductivity.

Roh et al. (2009) have developed a metal compositeembroidery yarn (MCEY), which consists of threestrands of silver-plated copper filaments (40 mm in

diameter) processed with polyester filaments (Figure 7).Using MCEY as the upper yarn or the lower yarn of aCNC embroidering machine, they embroidered preciseelectrical circuits on a textile substrate with ease,without any design constraints. The MCEY that wasused as the upper yarn of CNC embroidering has beenprocessed with higher TPM (turns per metre) com-pared to the MCEY that was used as the lower yarn toprovide better mechanical properties. The resultingupper (U-) MCEY yarn had a yarn thickness of 286mm and an electrical resistance of 3.89 O/m. On thecontrary, the lower thread of CNC embroideringshould be thin and pliable, and thus, the lower (L-)MCEY has been produced to have a yarn thickness of272 mm and the electrical resistance was 3.88 O/m. Byusing the lower-embroidery method, line gaps betweenthe MCEY lines could be controlled to 0.6 mm, whilewith the upper-embroidery method 1 mm was thenarrowest line gap possible.

2.3. Conductive textile patches

2.3.1. Metal-coated fabric patch and ground

To be used as antenna patches and ground planes,conductive textiles must possess the following char-acteristics: (1) a surface resistivity below 1 O/sq, (2) ahomogeneous sheet resistance and (3) flexible butinelastic mechanical properties to ensure uniformelectrical properties (Locher et al. 2006, Zhu andLangley 2009b). Silver-, copper-, nickel- or tin-platedsynthetic fabrics are commercially available, soldunder the trade names, Zelt, Flec Tron1, ShielditTM,Nora1, etc. Such metalised fabrics have been used inconstructing conductive patches and grounds of textileantennas owing to their low surface resistivity(51 O/sq), small variance in surface resistance andtheir flexible but inelastic properties. Laser beams canbe used to precisely cut conductive patches in thedesigned shapes.

Figure 4. Micrograph of a three-plied yarn of stainless steelfilaments (Bekinox1 VN 12/3 6 275 of BEKAERT).

Figure 5. Micrograph of embroidery yarns made of Ag-coated polymer filaments: (a) three-plied silver-coated polyester yarns(AGposs, Mitsufuji Textile Ind. Co., Ltd.) and (b) three-plied Ag-coated PBO (Syscom Technology Inc. 2005).


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2.3.2. Non-conductive textile substrates

Non-conductive textile substrates, which are used asdielectric layers between an antenna patch and aground plane, require constant thickness of a fewmillimetres and low permittivity (Locher et al. 2006).Thus, for a textile antenna to obtain dimensionalstability, highly resilient airy textiles such as a porousmesh of synthetic fibres (Locher et al. 2006), flexiblefoam (Hertleer et al. 2009), felt (Locher et al. 2006,Kennedy et al. 2009, Zhu and Langley 2009a), orpolar-fleece (Zhu and Langley 2009a) have been usedas non-conductive textile substrates (Table 3). In orderto design textile-based antennas, the electromagneticproperties of the materials to be used at the operatingfrequency bands must be known. For example, fromTable 3, the porous polyamide mesh fabric with athickness of 6 mm has a permittivity er ¼ 1.14 at afrequency of 2.4 GHz, and loss tangent is negligible(Locher et al. 2006).

2.3.3. Attachment

Antenna patches can be attached onto textile sub-strates by applying adhesives or sewing, but the

electrical permittivity and loss tangent of the substratematerial are known to be affected by the use ofadhesives. Locher et al. (2006) reported that thermallyactivated adhesive sheets showed the best resultsamong liquid textile adhesives, point-wise applicationof conductive adhesives, sewing and adhesive sheets, inbonding a conductive patch onto a non-conductivesubstrate fabric. By using thermally activated sheets, arelatively thin layer of adhesive that only penetratedthe surface of the conductive fabric was deposited,and thus, the patch sheet resistance and substratepermittivity of the conductive patch was left unaltered(Figure 8(a)). Sewing is also a commonly usedmethod due to the durability of the attachment,although it induces wrinkles on the antenna patch(Figure 8(b)).

Table 2. Characteristics of metal filaments and a polyester filament used in the metal composite yarns of Roh (2010).

MCY components (ID)

Stainless steel (SS)a

Silver-plated copperb

Polyester (P)Bare (Cub) Polyesterimide coated (Cuc)

SpecificationsDiameter (mm) 35 40 40 (Øtotal: 48) 0.103Linear density (dtex) 80 112 116 83 (36f)DC resistance (O/m) 735 13.4 13.7 n.a.Tensile propertiesYoung’s modulus (N/tex) 28.2 6.96 6.72 9.97Load at yield (N) 0.475 0.167 0.154 1.03Max. load (N) 0.863 0.288 0.329 4.35Strain (%) 36.2 16.7 20.7 13.2

aSS: Bekaert Bekinox1 VN 35/1 6 1, Belgium.bCub: TW-O, Cuc: TW-D, Elektrisola, Switzerland.

Figure 6. Air textured bi-component yarn containing twostrands of Ag-copper filaments by Ohmatex (2004a).

Figure 7. Micrographs of the MCEYs and the CNCembroidery process by Roh et al. (2009): (a) U-MCEY andU-embroidery and (b) L-MCEY and L-embroidery.


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2.4. Printed textile circuits

2.4.1. Printing

Printing, by the means of silk-screening or ink-jetdeposition, of conductive ink is one of the mostconvenient methods of introducing conductive materi-als onto textile substrates. Bidoki et al. (2005, 2007)suggested a simple, environmentally safe and econom-ical process for ink-jet metal deposition on a textilesubstrate using commercially available ink-jet printers(Figure 9). The textile substrate was first printed with areducing agent ink (ascorbic acid or hydroxylamine)and then with a metal salt ink (silver nitrate). When themetal salt comes in contact with the reducing agent,insoluble metallic particles are generated, which growvery quickly in different shapes. The thickness of thedeposited layer may be increased by repeating the ink-jet deposition process. The conductivity level of theink-jet deposited silver pattern on cotton fabric(8.76 6 104 S/m) dropped to one-third of that onPET transparency paper (2.71 6 105 S/m), wheresilver wire has a conductivity of 6.173 6 107 S/m.

2.4.2. Etching

As shown in Figure 10, by adopting etch patterning ofsilver-coated fabrics using PCB (printed circuit board)fabrication methods and equipment, the CircuiteXTM

technology of X-Static1 allows conversion from con-ventional PCB/PWB (printed wiring board) and flexboards to a fabric circuit (Sosnowski 2007, Noble

Biomaterials 2006). This technology offers the ability totransfer power and data in a highly electricallyconductive, lightweight, durable and flexible product.However, the drawbacks are the environmentallyharmful process and low durability of the silver coating.

3. Textile antennas

Three types of communication take place in smartclothing systems: internal communication, personalspace communication and external communication.Internal communication refers to data transfer amongseparate components of a distributed smart clothingimplementation, i.e. within the user’s clothing orbetween different smart clothing layers. Personal spacecommunication takes place when internal communica-tion components initiate data transfer with theenvironment without a centralised access point, andis restricted to the user’s close proximity. Third,external communication is data transfer between smartclothing and external information networks or otherusers (Rantanen and Hannikainen 2005).

In order to realise wireless reception and transmis-sion of data for such on-body and off-body commu-nication, antennas must be integrated into clothing(Proetex 2004). As textile-based antennas are flexible,conformable and light, they can be easily integrated intoclothing. Therefore, textile-based antennas are suitablefor human body-centric wireless communication.

In the RF antenna industry, common antennaoperating frequencies are 125 kHz, 13.56 MHz, FM

Table 3. Dielectric properties of various non-conductive textile substrates.

Materials

Polyamide mesh(Locher

et al. 2006)

Foam(Hertleeret al. 2009)

Woolen felt(Locher

et al. 2006)

Nomex felt(Kennedyet al. 2009)

Fleece(Zhu and

Langley 2009)

Thickness (mm) 6 3.94 3.5 6.35 2.55Permittivity (er0) 1.14 1.52 1.45 1.18 2.17Loss tangent (d) Negligible 0.012 0.02 0.004 0.0035

Figure 8. Attachment of metal-coated fabric patches on non-conductive textile substrates: (a) thermally activated adhesivebonding of Ni-/Cu-/Ag-coated nylon on a polyamide mesh (Troster 2005, Locher et al. 2006) and (b) Ni-/Cu-/Ag-coated nylonsewn equiangular spiral antenna on polyester cloth (Kennedy et al. 2007).


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broadcast band (87 MHz to 107.5 MHz), 433 MHz,800/900 MHz, 2.4 GHz or even 5 GHz and beyond.Low-frequency (LF) systems are used as inductivenear-field link of RF fields for data communicationand powering, while higher frequency systems are usedfor microwave scattering and radiation, and thus thedata transmission rate can be increased with higherfrequency carrier far-field communication systems(Hum 2001, Mayer 2009). Therefore, in near-fieldcommunication (NFC), the distance of communicationis considerably less than RF carrier wavelength,while in far-field communication (FFC) systems,used in most traditional radios, the communicationdistance considerably exceeds the carrier wavelength(Sarpeshkar 2010).

In this section, various wearable textile antennasare reviewed. Antenna types, the materials used andfabrication methods along with their characteristicsand applications are listed and discussed. The humanbody effect and antenna flexure, which are importantfactors to be considered when designing wearabletextile antennas, are also reviewed. A variety ofwearable textile antennas for near-field communication(NFC) and for far-field communication (FFC) aresummarised in Tables 4 and 5, respectively.

3.1. Inductively coupled near-field communication(NFC)

Near-field communication (NFC) is a short-rangewireless communication technology in the LF andhigh-frequency (HF), bands, which allows simpleintuitive initialisation of the wireless network to non-self-powered devices. A tight, low power, non-propa-gating magnetic field between the devices, where twoinductive coils located within each other’s near field,effectively form an air-core transformer (Figure 11)(Mayer 2009). Nowadays, inductive coupling comes intothe forefront for various smart interactive textilesystems as low energy consumption NFC. As thestrength of the inductive RF fields (H) decays to thethird power of distance (r) (jHj * 1/r3) and the powertransmission loss between coils decays with the trans-mission distance to the power of 6 (PTag * 1/r6), therange of the inductive RF fields can be restricted to thesurface of the clothing and not radiate into the body.Also, the zone of communication is mainly localised tothe overlapping regions of the RF antennas (Hum2001). According to the law of induction, the open-circuit voltage of the coil can be increased by enlargingthe coil diameter, increasing the number of turns andreducing the conductor width. But additional turnscause losses in the antenna that are related to the totalresistance of the spiral conductor. The most efficientantenna can be constructed by optimising the number ofturns and the width of the conductor, given fixeddimensions (Mayer 2009).

3.1.1. NFC for internal communication

The first attempt for applying near-field inductivecoupling of RF fields to on-body communication wasmade by Hum (2001). To enable wireless communica-tions across different pieces of clothing and gaps,named a fabric area network (FAN), repeater RF linksare implemented like a hopping network of transfor-mer chains. The FAN was based on 125 kHz RFID

Figure 10. Fabric PCB by etching with spandex flexibility: CircuiteXTM by X-static1 (Sosnowski 2007).

Figure 9. Silver-printed inductive coil on cotton fabric(Bidoki et al. 2007).


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(Radio-Frequency Identification) technology with an-tenna coils with a square outline of 5 cm on each sidewith 15 turns of 0.25 mm insulated wires (Figure12(a)). Antennas were routed to the trouser pockets(front and back), shirt pockets, cuffs of the trousers,sleeves, the back of the shirt and other locations. Theseantennas can then be used to communicate withtransponder chips that are embedded in the wallet,shoes, pens, watches, accessories or personal items in aback-pack that is slung on the back or shoulders(Figure 12(b)).

Similarly, Yoo et al. (2009) have also developed aninter-clothes network using inductive coupling betweenwoven square spiral inductors with 2.5 mH inductance(Figure 13(a)). They used a conductive core spun yarnof KITECH (Korea Institute of Industrial Technology)that is composed of seven strands of 10 mm copper alloyfilaments insulated with fluorine resin (Figure 13(b)).The DC resistance and linear density of the conductiveyarn were 7.5 O/m and 175 Tex, respectively (Chung2009). The yarn was hand stitched on the garment tocreate the inductors, thus there are limitations inconstructing precise circuits with this yarn.

Locher et al. (2004) reported a locomotion sensorwithin a textile-based wireless body area network(WBAN) system motivated by the principle of RFIDtechnology. They chose the carrier frequency in theindustrial, scientific and medical (ISM) band of6.78 MHz, but they failed in matching the targetfrequency. The autonomous locomotion sensor systemwas embedded in the boot, including battery, control

logic and inductive transmitter (TX, 3.1 mH). Theconductive yarn embroidered receiver (RX, 27 mH) inthe trouser leg overlaid the TX and received signals viainductive coupling despite much smaller field strengths(Figure 14(a)). Similarly, Figure 14(b) shows embroi-dered coils used for inductively coupled interconnec-tion between an mp3-player box and earphones in ajacket (Troster 2005).

3.1.2. NFC for personal space communication

Catrysse et al. (2004) reported textile sensors forwireless electrocardiograms (ECG) and respirationrate monitoring of hospitalised children. For wirelesstransmission of the recorded data from the body-wornsensors to a base station, the primary coil wasintegrated in the mattress, and the secondary coil, onthe suit. The secondary coil was a 6-turn circular spiralinductor with a diameter of 12.5 cm, constructed witha stainless steel yarn with an inductance value of2.9 mH and quality factor of 0.72 at 700 kHz (Figure15(a)). The inductive link operated within a maximumcoil separation range of 6 cm at a frequency of700 kHz. Coosemans et al. (2006) constructed abody-worn transponder antenna embroidered with acomposite yarn made of stainless steel yarns anda copper core (electrical resistance: 0.20 O/m), tomonitor ECG as an embedded patient monitoringsystem (Figure 15(b)). The inductance of the 10 cm-diameter embroidered coil was 13.7 mH, and thequality factor was 17.2 at 132 kHz. The coil of the

Table 4. Wearable textile antennas for near-field communication (NFC).

Antenna type Frequency Fabrication method SizeSpecifications,applications

For internal communicationSquare coil by Hum(2001)

125 kHz Attachment of 15 turns of 0.25-mminsulated wire

5 cm 6 5 cm FAN, non-textileprocessibility

Square coil by Locheret al. (2004)

6.78 MHz 15 turns of conductive yarn (27 mH) – WBAN forlocomotionanalysis

For personal space communicationCircular coil by Catrysseet al. (2004)

700 kHz Appliqued 6-turn spiral inductor(diameter: 12.5 cm)

12.5 cm Operating distance of6 cm at 700 kHz

Circular coil byCoosemans et al.(2006)

132 kHz Embroidery of a stainless steelfilament wrapped copper core yarn

*10 cm WBAN, Limitedcircuit design

Multi-turn rectangularloop RFIDtransponder by Reichlet al. (2006)

13.56 MHz 3-layered jacquard woven Au-/Ag-coated polyamide filaments

46 cm 6 6 cm Over 50-cm readoutdistance

Dual multi-turn circularloop RFID reader/transponder by Roh(2010)

13.56 MHz CNC embroidery of MCEY (Linz2009); TX: 4 turn outer loop/6 turninner loop with 1 cm line intervals;RX: 6 turn outer loop/10 turn innerloop with 1 mm line intervals

TX: 28 cm;RX: 6.5 cm

WBAN within 1 m


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transponder antenna had a limited winding density dueto the fabrication method, so the optimal number ofturns could not be attained.

Kallmayer et al. (2003) and Reichl et al. (2006)constructed 13.56 MHz textile transponder antennasfor smart labels to be used in hospitals, which could bewashed at 958C, pressed with 28 bar and dried above1008C. The textile transponder antenna was woveninto a three-layered weave on a jacquard loom (Figures1 and 16), as mentioned in section 2.1.1., using a Au-plated Ag-coated polymer yarn. Additional Au-platingof 1–2 mm was deposited on a commercially availableAg-coated polyamide yarn, reducing the resistance ofthe yarn to about 14 O/m, and permitting a readingdistance of about 50 cm with the Philips i-code System.

Small modules (2 6 4 mm2) were connected to theantenna, and by using commercial glob top material,which is often used in chip-on-board technology, a thinencapsulation was created. Jung et al. (2003) alsoreported a similar approach using insulated metalwires as warp and weft in a single-layer fabric (Figure2(a)) to fully embed the antenna structure into thefabric in an unobtrusive but secure way.

A new approach for WBAN, consisting of a set ofmobile and wearable intercommunicating sensors thatcan be used for monitoring real-time vital bodyparameters or movements has been suggested. Roh(2010) proposed an embroidered multi-turn loopantenna system based on 13.56 MHz RFID technol-ogy (Figure 17), using the above-mentioned MCEYembroidering method in section 2.2.3 and Figure 7.Clothing provides sufficient area for placing thetransmitting antenna (maximum diameter: 28 cm),while the size of the receiving antenna (maximumdiameter: 6.5 cm) was limited to that of the mobiledevice. The dual multi-turn loop structure of Roh’santenna, where a pair of inner and outer multi-turnloops was embroidered on the same fabric plane andconnected to the port in parallel, reduced the DCresistance and increased the mutual inductance be-tween the inner and outer loops. When worn on thebody, the resonance frequency of the antenna droppedfrom that measured in free space due to human bodylosses. To operate well, both on and off the body, theinner loop of the transmitter antenna was tuned toresonate at 13.56 MHz in free space and the outer loopwas tuned to resonate at 15.2 MHz in free space, eachusing the appropriate series capacitor. S21 fromtransmitting antennas on a body-phantom to the

Figure 11. Principle of inductive coupling between readerand transponder (Mayer 2009).

Figure 12. Fabric area network by Hum (2001): (a) wireless transfer of RF energy across two antenna coils built on fabrics and(b) base-station layer supplying power to devices attached on clothing (left) and set up of wireless communications with a bagcontaining contents (such as cellphones) that have transponder chips embedded (right).


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receiving antenna was 735 dB and 737 dB atoperating distances 50 cm and 75 cm, respectively.

3.2. Far-field communication (FFC) for externalcommunication

In order to operate well irrespective of the presence ofthe human body, broadband antennas, array antennasand multiband antennas are preferred as wearableantennas. Owing to their inherent wideband character-istics, such antennas are less affected by the impedancemismatch caused by human body losses and bodymovements.

3.2.1. Dipole antennas

3.2.1.1. Folded dipole antennas. Visser and Reniers(2007) developed a wearable embroidered foldeddipole array antenna to be used in a wearable

communication system, which was a 2.45 GHz two-element LPFDA (Log Periodic Folded Dipole Array)antenna. As shown in Figure 18, the antenna washand-embroidered onto a cotton fabric using astainless steel yarn. This antenna had good inputmatching over a wide frequency band but theresonance frequency shifted from the required2.45 GHz, both in free space and on the upper arm.In free space, the return loss was over 7.0 dB from1.95 GHz to 2.25 GHz, and the maximum return losswas about 11.8 dB at 2.2 GHz, while on the arm, themaximum return loss was 12 dB at 1.8 GHz. Thiseffect was due to the fact that the tolerances on theantenna construction have not been tight because ofthe stretching of the cotton substrate duringfabrication, as well as the coupling effect of thehuman body.

Roh et al. (2010) have also considered the humanbody effect when designing an embroidered wearable

Figure 14. Textile coils for inductive signal transmission: (a) wireless locomotion analysis system (Locher et al. 2004) and (b)wireless connection of mp3-player to jacket (Troster 2005).

Figure 13. Inter-clothes network using inductive coupling between textile inductors by Yoo et al. (2009): (a) illustration of inter-clothes network and (b) hand embroidered square spiral inductors using the conductive core spun yarn.


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multi-resonant folded dipole (MRFD) antenna for FMsignal reception. The antenna was produced usingCNC embroidering of MCEY (Figure 7(b) and Figure19). As the human body has very high relativepermittivity, the presence of a human body close to

an antenna reduces the efficiency of the antenna andlowers the resonance frequency, where both effectsdepend on the distance between the antenna and thebody. Furthermore, the movement of the body de-forms the spatial geometry of the body-worn antenna

Table 5. Wearable textile antennas for far-field communication (FFC).

Antenna type Frequency Fabrication method SizeSpecifications,applications

Log-periodic foldeddipole array (Visserand Reniers 2007)

2.45 GHz Hand embroidery of stainlesssteel yarn on cotton fabric

– Wider bandwidth

Multi-resonantfolded dipole (Rohet al. 2010)

87–107 MHz MCEY CNC embroidery onpolyester woven fabric

144 cm 6 10 cm Broadband

Equiangular spiral(Kennedy et al.2007)

2–4 GHz Ni-Cu-Ag nylon (Nora1, 0.03O/sq) spiral antenna sewn onpolyester cloth

60.9 mm (outer radius) Broadband, spacesuit

Truncated cornermicrostrip patch(Hertleer et al.2009)

2.4–2.4835 GHz Metal-coated fabric antennapatch (ShielditTM) andground (Flectron1):50.1 O/sq, fire-resistant/water-repellent foamsubstrate (3.94 mm)

50 mm (L) 6 46 mm(W) 6 8 mm (insetside length)

Wider bandwidth,firefighter’s vitalsign monitoring(Proetex project)

Microstrip patch(Hertleer et al.2008)

1.56342 GHz,1.58742 GHz

73.5 mm(L) 6 69.5 mm(W) 6 5 mm (insetside length) (Ground:130 mm 6 130 mm)

Global PositioningSystem (GPS)(Proetex project)

Eight-elementmicrostrip patcharray (Kennedyet al. 2009)

2.45 GHz Ni-Cu-Ag-coated nylon(Nora1, 0.03 O/sq) patchand ground, Nomex1 Feltsubstrate (6.35 mm)

4.85 cm squarepatch 6 8

Wider bandwidth,extravehicularactivity space suit

Complementary-8wideband(Kennedy et al.2009)

2.1–10 GHz 15.32 cm (L) 612.2 cm (W)

Broadband,extravehicularactivity space suit

Dual-band coplanarpatch (Zhu andLangley 2009a)

2.45 GHz, 5 GHz Cu-Sn plated nylon (50.01 O/sq) patch and EBGmaterials, felt substrate(1.1 mm)

Antenna:55 mm 6 55 mmEBG: 120 mm 6120 mm

Dual-band, widerbandwidth, goodgain, SAR (specificabsorption rate)reduction

Figure 15. Textile coils for ECG monitoring suits: (a) appliqued coils of stainless steel yarn for inductive links (Catrysse et al.2004) and (b) embroidered transponder antenna made with a composite yarn of stainless steel yarns and a copper core(Coosemans et al. 2006).


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and affects the performance of the antenna as well.Thus, to compensate for the human body effect, awearable embroidered FM antenna should be designedto be well matched over a wider frequency band thanthe FM broadcast band (about 87 to 130 MHz). Theembroidered FM antenna of Roh et al. comprised fiveindividual MCEY embroidered-folded dipoles con-nected in parallel so that the bandwidth could bebroadened via multiple resonance. The antenna wasattached to a jacket, stretched from the left forearm,over the shoulder and to the right forearm. When theantenna was worn, the radiation pattern and gain weregreatly influenced by the body and arm postures. Theproposed antenna provides a wide operating band of80.5 MHz to over 130 MHz at 5 dB return lossregardless of the arm movements, satisfying the FMbroadcast band (87.5 MHz to 108 MHz). In freespace, the maximum gain of the MCEY FM antennawas 0.68 dBd. When the arms were moved, the antennaradiated different polarisation, giving a deformedtoroidal radiation pattern, and the gain of this body-worn antenna ranged from 77.08 to 715.79 dBd inthe FM broadcast band regardless of the armsmovement.

3.2.1.2. Bow-tie dipole antennas. Figure 20 shows anAg-coated polyamide yarn (X-static1, NobelBiomaterials) embroidered broadband bow-tie

antenna developed by MegaWave Corp. (Sosnowski2007) and a copper-coated-fabric patched bow-tieantenna by Matthews and Pettitt (2009). Based onRF performance, the most attractive method ofconstructing a textile-based bow-tie antenna is usingconductive patches of metal-coated fabric. Accordingto Matthews and Pettitt (2009), the copper-coated-fabric patched bow-tie antenna gave excellent resultswhen compared to other fabrication methods such asembroidering conductive yarns or conductive printing.

3.2.1.3. Spiral dipole antennas. Kennedy et al. (2007)developed a fabric equiangular spiral antenna designedfor 2–4 GHz operation of which wideband nature waswell suited for spacesuit application (Figure 8(b)). Thetwo arms of the spiral, made of silver-copper-nickelplated nylon fabric with a thickness of 0.06 mm andsurface resistivity of 0.03 O/sq (Nora, Shieldex1 byStatex), were sewn onto a polyester cloth (thickness:

Figure 16. Textile transponder antenna (13.56 MHz)composed of three different layers, where a coil made ofnon-insulated conductive warp and weft of Au/Ag-coatedpolyamide yarns are only in contact at the corners to formmulti-turn loops by TITV and Fraunhofer IZM (Reichl et al.2006).

Figure 17. Embroidered dual multi-turn loop RFIDantennas for WBAN: (a) transmitting antenna with a 4-turn outer loop and 6-turn inner loop with 10 mm lineintervals and (b) receiving antenna with a 6-turn outer loopand 10-turn inner loop with 1 mm line intervals (Roh 2010).

Figure 18. 2.45 GHz two-element LPFDA antenna madeof stainless steel yarn embroidered on a cotton fabric (Visserand Reniers 2007).


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0.43 mm, tand: 0.070). This e-textile equiangular spiralantenna showed a similar voltage standing wave ratio(VSWR) response to the conventional copper spiralarms and simulation.

The wearable textile spiral antennas shown inFigure 21 were designed to work as wideband solutionsfrom 100 MHz to 1 GHz by Matthews and Pettitt(2009). They have used different fabrication methodssuch as (a) conductive fabric patch, (b) conductiveyarn embroidering, or (c) conductive paint, forproducing the antennas. The conductive nylon patchspiral antenna showed the best RF performanceamong the three methods, where the return loss ofthe body-worn antenna was better than 12 dB over thefrequency range of 100 MHz to 1 GHz and the gainwas higher than that from simulation (maximum gainwas about 73 dB at 500 MHz). The embroideredspiral antenna showed the lowest gain due to thelossyness of the material and the contact resistancebetween the embroidered conducting yarns. Theperformance of the painted antenna containing silverleaf was comparable to the conductive nylon patch,but the paint could crack with repeated flexing and thehigh price was another drawback.

3.2.2. Patch antennas

3.2.2.1. Microstrip patch antennas. Textile microstrippatch antennas usually consist of a metal-coated fabricantenna patch bonded to an insulated dielectricsubstrate that has a ground plane on the oppositeside of the substrate. They are simple to fabricate, easyto modify, suitable for simulation on common wavesolvers, and they feature good properties. Thus, avariety of textile microstrip patch antennas has beendeveloped for far-field communication of smart textilesystems, usually operating in the 2.4 GHz ISM band.

The Proetex project, of which the goal is to improvethe safety and efficiency of emergency workersby empowering them with wearable sensing andtransmission systems that monitor their health,activity, position and their environment during variousrisky situations (Proetex 2004), has proposed a variety oftextile patch antennas integrated into a firefighter’sprotective coat to transmit the firefighter’s life signs,environment and position to a nearby base station(Hertleer and Langenhove 2007, Hertleer et al. 2008,Hertleer et al. 2009, Vallozzi et al. 2009). Figure 22shows a wearable microstrip patch antenna, which wasmade of a metal-coated fabric patch, ground and non-conductive aramid fabric substrate comprising the outershell of a fire-fighter’s coat, designed for operatingaround 2.45 GHz for short-range communication(Hertleer and Langenhove 2007). Hertleer et al. (2008)reported that a rectangular ring-shaped e-textile

Figure 19. MCEY embroidered MRFD antenna for FM reception: (a) design and embroidered product and (b) embroideredMRFD antenna positioned on the shoulder of a jacket with arms outstretched (Roh et al. 2010).

Figure 20. Textile broadband antennas: (a) Ag-platedpolyamide yarn embroidered bow-tie antenna byMegaWave Corp. (Sosnowski 2007) and (b) a copper-coated-fabric patched bow-tie antenna (Matthews andPettitt 2009).


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microstrip patch antenna on a fleece substrate had anefficiency of more than 75%, which was comparable toconventional non-textile antennas. Several studies(Locher et al. 2006, Hertleer et al. 2009) on the effectsof antenna flexure on the input impedance and radiationcharacteristics of e-textile microstrip patch antennasreported slight detuning of the antenna elements withflexure. Thus, the antennas are designed to cover a largebandwidth in order to account for shifts due to bending.Also, as the linear dimension of the patch antennaincreases when the antenna is bent outward, an increasein beam width and reduction in gain was observed(Kennedy et al. 2007).

3.2.2.2. Microstrip patch antenna array. As smartantenna array systems are designed to be highly

adaptable to a dynamic communication channel, on-body antenna systems are likely to benefit from theaddition of antenna arrays, which can compensate forsome of the deficiencies occurring under flexure andwrinkling of a body-worn antenna. An antenna arrayis basically a group of identical antennas arranged andinterconnected for achieving greater gain or beamshaping. In this context, Kennedy et al. (2007, 2009)constructed an eight-element e-textile microstrip patcharray (Figure 23) for the 2.45 GHz ISM frequencyband to be placed on an extravehicular activity spacesuit. The elements are linearly polarized patchantennas, where each square patch made of a metal-coated fabric (Nora, 0.03 O/sq) measured 1.85 cm onthe side and was affixed to a Nomex felt (Table 3). Asexpected, the array showed good impedance

Figure 21. Wearable textile spiral antennas: (a) conductive nylon patch spiral (b) embroidered conductive yarn spiral and (c)conductive paint spiral (Matthews and Pettitt 2009).

Figure 22. Textile microstrip patch antennas (2.45 GHz) integrated into textile layers (Hertleer and Langenhove 2007).


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performance with slight wrinkling and the main beamwidened with outward bending.

3.2.3. Ultra-wideband antennas

Kennedy et al. (2009) also designed an ultra-widebandantenna for use above 2.1 MHz, which was namedas a complementary 8-wideband e-textile antenna(Figure 24). With the self-complementary structureintroduced to help with impedance matching and togenerate polarisation diversity from a single element,this antenna showed acceptable wideband impedanceperformance from 2.1 to 10 GHz. And, as shown inFigure 24, a low-mass multiple-antenna system of sixcomplementary-8 wideband antenna elements wasplaced around the periphery of an extravehicularactivity (EVA) space suit, where pattern diversity wasimplemented by rotating the antenna elements.

3.2.4. Coplanar antenna

As coplanar antennas have much wider bandwidththan microstrip patch antennas, Zhu and Langley(2009a) designed a wearable textile dual-band copla-nar antenna covering the 2.45 GHz and the 5 GHzwireless networking band (Figure 25). The antennawas integrated with an electromagnetic band gap(EBG) substrate that has a potential advantage ofreducing the backward radiation from the antennaand hence reducing the radiation absorbed by thebody, rendering the antenna tolerant to human bodyeffects. This antenna consisted of an inner patchsurrounded by a parasitic rectangular ring element,surrounded by the normal ground of coplanar feedline (55 mm 6 55 mm), and an EBG ground plane(120 mm 6 120 mm). The conducting material usedwas a copper- and tin-plated nylon fabric, ZeltTM,which was attached to a thin felt of 1.1 mm. Theoverall thickness of the antenna was 4.48 mm. Theresulting antenna showed broader operating band-width, comparable gain and reduced radiation

absorption of the body when compared to anequivalent microstrip patch antenna. But underbending condition, the resonance frequency droppedby 2%.

4. Conclusions

Wearable textile antennas are of great interest, as thedemand for wireless on-body and off-body

Figure 23. Eight-element e-textile microstrip patch antennaarray (Kennedy et al. 2009).

Figure 24. Six complementary-8 e-textile antennas posi-tioned around an EVA suit (Kennedy et al. 2009).

Figure 25. Dual-band coplanar textile antenna on EBGarray plane (Zhu and Langley 2009a).


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communications for smart clothing systems increases.As everyday clothing provides sufficient area to placeantennas, which usually require relatively largespace, and textile antennas ensure wearing comfortowing to their flexibility and lightness, the potentialapplications of textile antennas are diverse, rangingfrom medical applications to protective, military andspace applications. A variety of wearable textileantennas were reviewed in this article, including theirfabrication methods, antenna types, and applicationfields, in order to provide background information andapplication ideas for designing wearable textileantennas.

Owing to the high conductivity of metals, variousMCYs and fabrics are used to manufacture RFengineering textiles. For linear antenna circuits, CNCembroidering of MCYs is a suitable constructionmethod, because this method offers prompt and precisecircuit design variability, a simple and eco-friendlyprocess as well as reasonable antenna performance. Toconstruct patch antennas, metal-coated fabrics are themost suitable for both the ground plane as well as theantenna patch.

As the characteristics of wearable antennas aregreatly affected by human proximity and motion,broadband antennas and array antennas are preferredto compensate for the impedance mismatch caused bythe presence of human body losses and movements.For inductively coupled near-field communication,which can provide internal and personal space com-munication in smart clothing, a variety of woven orembroidered multiturn loop antennas were suggestedfor WBAN application. For far-field communicationin smart clothing, many different types of broadbandtextile antennas were developed to compensate for thedetuning caused by the human body, such asembroidered folded dipole array antennas, metal-coated fabric-patched bowtie and spiral dipole anten-nas, a microstrip patch antenna array and a coplanarantenna made of metal-coated fabric patch and groundplane. Especially, textile antenna arrays, both of linearand planar antennas, are suggested as a solution to theproblems defined as the limitations of single body-worn textile antennas.

References

BEKAERT, 2006. Bekinox1 VN Continuous stainless steelfilament yarn. Brochure 2006.

Bidoki, S.M., et al., 2005. Inkjet printing of conductivepatterns on textile fabrics. AATCC Review, 5 (6), 17–22.

Bidoki, S.M., et al., 2007. Ink-jet fabrication of electroniccomponents. Journal of Micromechanics and Microengi-neering, 17, 967–974.

Catrysse, M., Puers, R., and Hertleer, C., 2004. Towards theintegration of textile sensors in a wireless monitoring suit.Sensor Actuators A – Physics, 114, 302–311.

Chung, G., 2009. Digital garment for data communicationusing digital yarn. Korean-German Smart Textile Sympo-sium, 1–2September 2009Seoul:KOFOTI&KITECH, 60.

Costs Technical Services, 2007. All about sewing threads,Bulletin Post [online]. Available from: http://www.coatssewingsolutions.com/sewingsolutions/download/Bulletin07_AllAboutThreads.pdf [Accessed 18 June 2010].

Coosemans, J., Hermans, B., and Puers, R., 2006. Integratingwireless ECG monitoring in textiles. Sensors andActuators A – Physics, 130–131, 48–53.

Dobbins, J.A., et al., 2006. Fabric equiangular spiralantenna. Antennas and Propagation Society InternationalSymposium, 9–14 July 2006 Albuquerque, New Mexico:IEEE, 9–14.

Ghosh, T.K., Dhawan, A., and Huth, J.F., 2006. Formationof electical circuits in textile substrates. In: Mattila, H.R.,ed. Intelligent textiles and clothing. Cambridge, UK:Woodhead, 239–246.

Gimpel, S., et al., 2004. Textile-based electronic substratetechnology. Journal of Industrial Textiles, 33 (3), 179–189.

Hertleer, C. and Langenhove, L., 2007. A textile antenna forfire fighter garments. AUTEX (Association of Universitiesfor Textiles) 2007 Conference: From Emerging Innova-tions to Global Business, 26–28 June 2007 Tampere,Finland [CDROM], Autex.

Hertleer, C., et al., 2008. The use of textile materials to designwearable microstrip patch antennas. Textile ResearchJournal, 78 (8), 651–658.

Hertleer, C., et al., 2009. A textile antenna for off-bodycommunication integrated into protective clothing forfirefighters. IEEE Transactions on Antennas and Propaga-tion, 57 (4–1), 919–925.

Hum, A.P.J., 2001. Fabric area network – a new wirelesscommunications infrastructure to enable ubiquitousnetworking and sensing on intelligent clothing. ComputerNetworks, 35, 391–399.

Jung, S., et al., 2003. Enabling technologies for disappearingelectronics in smart textiles. International Solid-StateCircuits Conference (ISSCC’03), 9–13 February 2003San Francisco: IEEE, 386–387.

Kallmayer, C., et al., 2003. New Assembly ofTechnologies for Textile Transponder Systems. Proceed-ings of the 53rd Electronic Component and TechnologyConference, 30–30 May 2003 New Orleans: IEEE, 1123–1126.

Kellomaki, T., Heikkinen, M., and Kivikosh, M., 2006.Wearable antennas for FM reception. First EuropeanConference on Antennas and Propagation (EuCAP 2006),6–10 November 2006 Nice, France: ESA [CDROM].

Kennedy, et al., 2007. Potential space application for body-centric wireless and e-textile antennas. Seminar onAntennas and Propagation for Body-Centric WirelessCommunications, 24 April 2007 London: IET, 77–83.

Kennedy, T.F., et al., 2009. Body-worn e-textile antennas: thegood, the low-mass, and the conformal. IEEE Transac-tions on Antennas and Propagation, 57 (4), 910–918.

Kirstein, T., 2005. Smart clothing. In: Lecture of WearableSystems II. Zurich: Wearable Computing Lab, ETH.

Linz, T., 2009. New integration technologies for electronicsin textiles. Korean-German Smart Textile Symposium, 1–2September 2009 Seoul: KOFOTI & KITECH, 27–53.

Linz, T., Kallmayer, C., and Aschenbrenner, R., 2005.Embroidering electrical interconnects with conductiveyarn for the integration of flexible electronic modulesinto fabric. Ninth International Symposium on WearableComputers, 18–21 October 2005, Osaka: IEEE, 86–89.


Dow

nloa

ded

by [

Uni

vers

ity o

f T

oron

to L

ibra

ries

] at

09:

46 0

6 Ju

ly 2

011

http://www.coatssewingsolutions.com/sewingsolutions/download/Bulletin07_AllAboutThreads.pdf











Locher, I. and Troster, G., 2007. Fundamental BuildingBlocks for Circuits on Textiles. IEEE Transactions onAdvanced Packaging, 30 (3), 541–550.

Locher, I., et al., 2004. Wireless, low-cost interface for bodyarea networks. The Eighth International Symposium onWearable Computers (ISWC’04), 31 October – 3November 2004, Virginia, USA: IEEE, 170–171.

Locher, I., et al., 2006. Design and characterization of purelytextile patch antennas. IEEE Transactions on AdvancedPackaging, 29 (4), 777–788.

Locher, I., 2007. Sensing and illumination with smart fabrics2007, 7–9May,Washington,DC. IntertechPira [CDROM].

Mallet, E. and Du, R., 1999. Finite element analysis ofsewing process. International Journal of Clothing Scienceand Technology, 11 (1), 19–36.

Massey, P., 2001. Mobile phone fabric antennas integratedwithin clothing. 11th International Conference on Anten-nas and Propagation, 17–20 April 2001 Manchester, UK:IEEE, 480 (1), 344–347.

Matthews, J.C.G. and Pettitt, G., 2009. Development offlexible, wearable antennas. Third European Conferenceon Antennas and Propagation, 3–27 March 2009 Berlin:EurAAP, 273–277.

Mayer, L.W., 2009. Antenna design for future multi-standard and multi-frequency RFID systems. Thesis(PhD), Wien University.

NASA, 2007. Not-so-heavy metal: electrical conductivity intextiles [online]. Available from: http://www.nasa.gov/vision/earth/technologies/electric_textiles.html [Accessed18 June 2010].

NobleBiomaterials, 2006.CircuiteXTM[online].Available from:http://www.noblebiomaterials.com/page.asp?itemid¼138[Accessed 18 June 2010].

Ohmatex, 2004a. Product datasheet: un-coated yarn [online].Available from: http://www.ohmatex.dk/pdfer/uncoated_yarn.pdf [Accessed 18 June 2010].

Ohmatex, 2004b. Smart textile–opening up new markets[online]. Available from: http://www.ohmatex.dk/pdfer/Ohmatex_brochure.pdf [Accessed 18 June 2010].

Post, E.R., et al., 2000. E-broidery: design and fabrication oftextile-based computing. IBM Systems Journal, 39 (3/4),840–860.

Proetex, 2004. Advanced e-textiles for firefighters and civilianvictims [online]. Available from: http://www.proetex.org/objectives.htm [Accessed 18 June 2010].

Proetex, 2009. Communications: integrated wireless net-work, textile antenna [online]. Available from: http://www.proetex.org/final%20proetex%20learning/communications.htm [Accessed 18 June 2010].

Rantanen, J. and Hannikainen, M., 2005. Data transfer forsmart clothing: requirements and potential technologies.In: Tao, X., ed. Wearable electronics and photonics,Cambridge, UK: Woodhead, 198–222.

Reichl, H., Kallmayer, C., and Linz, T., 2006. ElectronicTextiles. In: E.H.L. Aarts and J.L. Encarnacao, eds. Truevisions: the emergence of ambient intelligence. Berlin:Springer, 115–132.

Roh, J., 2010. Design and fabrication of conductive com-posite structures for smart textile systems. Thesis (PhD).Seoul National University.

Roh, J., Chi, Y., and Kang, T.J., 2009. Thermalinsulation properties of multifunctional metal compositefabrics. Smart Materials and Structures, 18 (2), 025018.

Roh, J., et al., 2008. Electromagnetic shielding effectivenessof multifunctional metal composite fabrics. TextileResearch Journal, 78 (9), 825–835.

Roh, J., et al., 2009. Characterization of embroideredinductors. Smart Materials and Structures.

Roh, J., et al., 2010. Embroidered wearable multi-resonantfolded dipole antenna for FM reception. IEEE Antennasand Wireless Propagation Letters, 9, 803–806.

Salonen, P. and Rahmat-Samii, Y., 2007. Textile antennas:effects of antenna bending on input matching andimpedance bandwidth. IEEE Aerospace and ElectronicSystems Magazine, 22 (12), 18–22.

Salonen, P., Keskilammi, M., and Kivikoski, M., 2000.Single-feed dual-band planar inverted-f antenna withu-shaped slot. IEEE Transactions on Antennas andPropagation, 48 (8), 1262–1264.

Sarpeshkar, R., 2010. Low power RF telemetry in biomedicalimplants. In: Ultra Low Power Bioelectronics: Funda-mentals, Biomedical Applications, and Bio-inspired Sys-tems. New York: Cambridge University Press, 489.

Shaw, R.K., et al., 2007. The characterization of conductivetextile materials intended for radio frequency applica-tions. IEEE Antennas and Propagation Magazine, 49 (3),28–40.

Simon, E., 2009. Embroidered interconnections. Korean-German Smart Textile Symposium, 1–2 September 2009,Seoul: KOFOTI & KITECH, 60.

Sosnowski, T., 2007. Smart textile – are you enabled. SmartFabrics 2007, 7–9 May, Washington, DC. InterPira[CDROM].

Sundaresan, G., Hari, P.K., and Salhotra, K.R., 1997.Strength reduction of sewing threads during high speedsewing in an industrial lockstitch machine: Part I –mechanism of thread strength reduction. InternationalJournal of Clothing Science and Technology, 9 (5),334–345.

Syscom Technology Inc., 2005. The metal clad polymer fiber:example of AmberStrandTM specifications. Brochure2005.

Tanaka, M. and Jang, J.H., 2003. Wearable microstripantenna. Antennas and Propagation Society InternationalSymposium, 22–27 June 2003. Ohio, USA: IEEE, 2, 704–707.

Troster, G., 2005. Review: The agenda of wearablehealthcare. IMIA Yearbook of Medical Informatics,125–138.

Vallozzi, L., Vandendriessche, W., and Rogier, H., 2009.Design of a protective garment GPS antenna. Microwaveand Optical Technology Letters, 51 (6), 1504–1508.

Visser, H.J. and Reniers, A.C.F., 2007. Textile antennas, apractical approach. Second European Conferenceon Antennas and Propagation, 11–16 November 2007Edinburgh: IET, 538–545.

Yoo, J., Lee, S., and Yoo, H.J., 2009. A 1.12 pJ/b inductivetransceiver with a fault-tolerant network switch formulti-layer wearable body area network applications.IEEE Journal of Solid State Circuits, 44 (11), 2999–3010.

Zhu, S. and Langley, R., 2009. Dual-band wearable textileantenna on an EBG substrate. IEEE Transactions onAntennas and Propagation, 57 (4–1), 926–935.

Zhu, S. and Langley, R., 2009. Dual-band wearable textileantenna on an EBG substrate. IEEE Transactions onAntennas and Propagation, 37 (4), 926–935.


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http://www.nasa.gov/vision/earth/technologies/electric_textiles.html

http://www.nasa.gov/vision/earth/technologies/electric_textiles.html

http://www.noblebiomaterials.com/page.asp?itemid=138

http://www.noblebiomaterials.com/page.asp?itemid=138

http://www.ohmatex.dk/pdfer/uncoated_yarn.pdf

http://www.ohmatex.dk/pdfer/uncoated_yarn.pdf

http://www.ohmatex.dk/pdfer/Ohmatex_brochure.pdf

http://www.ohmatex.dk/pdfer/Ohmatex_brochure.pdf

http://www.proetex.org/objectives.htm

http://www.proetex.org/objectives.htm

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Wearable Textile Antennas