FABRICSGET SMARTElectro-active textiles serve as switchesl sensorsl and more

STORY_JOSEPH OGANDO, SENIOR EDITOR

If your idea of "smart fabrics" is a pairof khaki pants that sheds food stains,think again. The smartest fabrics are be-coming electro-active, allowing them toaddressfar more important engineeringproblems than whether you wear yourlunch to an afternoon meeting. These

textiles can help you build flexible sens-ing systems, detect chemicals, generatemobile power and perform other tasks."More than 70 percent of the surfaces we

interact with daily are textiles. Oncethose textiles can carry data and electricalpower, it opens up a huge new world ofapplications," says Stacey Burr, presidentofTextronics Inc., a developer of smartfabric technology.

Rather than just a single material, »[www.designnews.com] 05.15.06 DESIGN NEWS 77

FABRICSGET SMART

electro-active smart fabrics encompassmany combinations of textiles and elet-trically conductive materials. Thoughoften based on elastomeric fibers, likeLycra, smart fabrics can be created froma wide variety of synthetic and even nat-ural fibers. Various knit, woven andnon-woven fabrics can all be made smart

too. k for the electrical properties,smart fabJjcs most commonly containfine metal wires, either in the yarn usedto make the fabric or woven into the

fabric alongside ordinary textile fibers.Other smart fabrics get their electricalproperties from inherently conductivepolymers or nanocomposites depositedas coatings on the fabric's fibers.

All of these electro-active smart fabrics

have a way to go before they becomecommonplace engineering materials.Some of the textiles, particularly thosethat rely on nanotechnology, are avail-able only in quantities suitable for devel-opment work. Others, while fully com-mercial, may not have enough of a trackrecord to alleviate the kinds of technical

concerns that design engineers bring upwithin minutes of evaluating a technolo-gy. "Smart fabrics are still something of ablack art," says Maggie Orth, presidentand founder ofInternational Fashion

Machines, a developer of smart fabricproducts.

Smart-fabric suppliers, for example,all make compelling arguments for theuse of their technologies in varioussensing systems. But only one compa-ny, Nanosonics Inc., would providetechnical data related to sensor perfor-mance - in this case, strain range, lin-

The ElekTexsensorcontainsa proprietary e-textile that senses pressure. It works by mea-suring voltage drop across the sensor surface.

earity and hysteresis.This lack of basic engineering infor-

mation may limit the use of smart fab-rics somewhat. Spyros Photopoulos, ananalyst who studies smart fabric marketfor Venture Development Corporation(VDC), recently surveyed OEMs re-garding their plans for using smart fab-rics and found that many expresseddoubts about the durability and perfor-mance of smart fabrics. "Price is also a

big issue," he says. "Many OEMswouldn't consider smart fabric technol-

ogywithout strong consumer demand."Smart fabrics may also suffer from a

disconnect within the design commu-nity. As Burr notes, "electrical engineersand textile designers don't speak thesame language." And bringing these twogroups together goes beyond semantics.Engineers need to know how to physi-cally integrate fabrics with traditionalrigid electronics, which requires new ap-proaches to interface and interconnectdesigns (see sidebar on page 82).

Eleksen's textile pressure sensor, which has seen use in keyboards for mobile electronics,

can be rolled, crumpled or folded without damage.

SWITCHESAND CONTROLS

The smart fabric applications that havecurrently moved along the furthest in acommercial sense have involved switchesand controls for consumer electronics.The leader in this field, Eleksen Ltd., hassupplied touch-sensitive fabric controlsfor products ranging from electronicscases to ski jackets with integrated, ma-chine-washable controls for audio play-ers. The company also developedportable wireless fabric keyboards thatyou can roll; fold or even crumple.

Eleksen makes these fabric controls

from a multilayered fabric containingthree electro-active layers. Two outerconductive layers surround an inner re-sistive layer that separates the conduc-tive layers until someone presses themtogether. k Andrew Newman, one ofthe technology's developers, explains,"the fabric is basically an open circuituntil someone presses the fabric." Elek-sen then measures the voltage drop atvarious points on the surfaces to deter-mine where and how hard someone

presses the fabric. "We measure the in-teraction in the x, y and z directions,"says Newman, who adds that the z-axismeasurement gives a relative, rather than

, an absolute, pressure reading.The company can supply a variety of

configurations, including single switchesor arrays of switches on a given fabric sur-face. The company's keyboards, for exam-ple, take the latter approach. Newmannotes that Eleksen's fabric, which it callsElek Tex, and the related electronics, out-put an analog signal. So the same technol-ogy can also be used for sliding controlbuttons, such as those used for volume or

scrolling on a computer display.While current Elek Tex applications

have focused squarely on consumer elec-tronics, Newman sees some potential fora variety of human-machine interface ap-plications. In automotive interiors andappliances, the technology could be usedfor software-configurable control panelsthat can cover even deeply curved sur-faces. In one of the only real indicationsof smart fabric durability, Eleksen has car-ried out extensive mechanical testing ofits products, including subjecting themto 10 million press cycles and hysteresistests after 30,000 roll-ups and folding cy-cles. "That's far in excess of what theywould see in real life," says Newman. (seehttp://rbi.ims.ca/4922-562 for the com-pany's reference designs).

Another switch application comesfrom International Fashion Machines.

Orth has re..:imagined the ordinaryhousehold light switch as a capacitivetouch sensor in the shape of a pom-pom.At first glance, pom-pom switches mayseem too frivolous for Design News' prac-tical readers. But consider this: Orth gets$129 for her light switch, which has ap-peared in museum shows, compared toabout two bucks for the ugly plastic com-modity versions down at the hardware

80 DESIGN NEWS 05.15.06 [www.designnews.com]

Smart fabrics arestill something of ablackart.

store. "Smart fabrics allowed me to create

a premium product," she says. She's alsomanaged to get UL approval for herswitch, no easy task.

SENSE STRAINAND MORE

For engineers, one of the biggest techni-cal potentials for smart fabrics relates totheir ability to sense strain and serve asthe basis for pressure monitoring systems.

FABRICS GET SMART

Both broad types of smart fabric - thosebased metal wires and those based on in-

herently conductive polymers ornanocomposites - can perform somesensing. Whatever the type of fabric, theytend to operate on the fabric equivalentof the piezoresistive principle. With fab-

~ rics based on metal wires, such as thoseoffered by Textronics, the movement ofthe fabric itself brings conductive metalfibers closer together or further apart, al-tering the resistance of the fabric. Some-thing similar happens with fibers infusedwith ICP or nanocomposites, in thatstrain changes the electron transport be-tween conductive clusters on the fabric

fiber. With some signal processing, theseresistance changes can be translated intopressure measurements. "In theory, youcan turn all kinds of resistive materials

into strain sensors," says Orth.Two of the newest ways to create fabric

sensors rely on nanotechnology to makepolymer fabric fibers conductive to vary-ing degrees. Nanosonic Inc. recently de-veloped smart fabrics based on an electro-static self-assembly process (see http://rbi.ims.ca/4922-563). Initially devel-oped to make free-standing elastomericsensor films, the self-assembly process caninfuse the surface of textile fibers with

various nanocomposites - combinationsof polymers and metals or metal oxides.Fabrics made from these fibers have highconductivity, with bulk resistivity valuesdown to 10-5ohm cm, according to An-drea Hill, the Nanosonics researcher whohelped develop the conductive fabrics.

At the same time, they also can tolerateextreme elongations. Rick Claus,Nanosonics president and founder, notesthat the original sensor films, called MetalRubber, can measure strains up to 1,000percent with full scale linearity of 1 per-cent. At lower strains, they can toleratethousands of flex cycles and exhibit low

Smart fabrics canbe seamlessly in-tegrated with ex-isting products.Here, Textronicsadded a heartmonitor electrodeto the lower bandof a sports bra.

FABRICS GET SMART

mechanical hysteresis, he adds. Thebrand new fabric versions, dubbed MetalRubber Textiles, can tolerate similarlylarge strains.

Another twist on inherently conduct-ing fibers comes from Eeonyx. The com-pany has a proprietary process for coatingtextiles with inherently conductive poly-mers based on doped polypyrrole. Thecompany polymerizes the materials insitu - or on the surface of the fabric it-

self-so that the coating material fills in-terstices in the surface and forms a physi-cal bond with the fibers. Jamshid Avloni,the company's president, reports that theICP doesn't offer conductivity near thelevel offered by metal wires. But, thenagain, it doesn't have to.

"There are orders of magnitude of dif-ferent between the conductivity of, say,polyester and copper," says Avloni. "Weoccupy a middle ground." The company

The basic lack ofinformation maylimit the use ofsmart fabrics.

The two nanotech approaches have adownside too. Metal Rubber Textiles and

Eeontex are currently available in quanti-ties that many large OEMs would con-sider developmental. What's more, Eeon-tex has issues with long-term stabilityowing to the hydrolysis of polypyrrolewhen exposed to elevated temperatures

1 and humid conditions. The company re-cently developed a third-generation prod~uct that improves stability by a factor of20, according to Avloni. And the fabricscan be protected with a laminate. But en-vironmental conditions still represent thechieffailure mode for the ICP and need

to be accounted for by design engineers,he acknowledges. "Metal wires have theirproblems too," he adds. "If you bendthem enough, they'll break."

In many sensing applications, smartfabrics won't likely represent a low-costalternative to an array of pressure trans-ducers. Yet even if they aren't cheapestway to sense pressure, fabric sensors canpotentially offer value by brining morefreedom to the design of sensing sys-tems. Fabrics can covering very large ar-eas, including civil structures. They canconform to a wide variety of surfaces,including the human body while it'smoving. And they may be able to mea-sure very large strains. Textronic's Burrnotes that elastomeric smart fabrics tol-

erate repeated elongations up to a fewhundred percent.

These fabric attributes may result inother types of unique sensors in the fu-ture. Textronics, for example, is workingon electro-optical movement sensors formedical monitoring applications. AsBurr explains, these sensors integrate alight source and photo detector into thefabric. As the fabric stretches and retUrns

to its initial shape, different amounts oflight would pass through the fabric's wo-ven or knit structure. Burr says one ap-

. plication for such an optical sensorwould be a garment that monitors a pa-t;.ient'sbreathing. Textronics also recently

. introduced a biomonitoring product forthe consumer market.

She also sees the potential for both op-tical and strain-based measurements ofmovement and vibration. And Nanoson-

ic's Claus reveals that the company hascome up with a proprietary chemical sen-sors based on smart fabrics. He's not

ready to publicly disclose much about it,other than to say that it works based onelectro-chemical reactions of a nanoclus-ters on the fabric surface.

82 DESIGN NEWS 05.15.06 [www.designnews.com]

can deliver fabrics, for example, with sur-face resistivities ranging from 10 to 106ohm/sq, controllable to within 10 per-cent. Avloni says the textiles have seensome use in piezoresistive pressure sens-ing applications, including a dynamicpressure sensor for biomedical applica-tions and the design of custom footwear.

Neither the Nanosonic nor the

Eeonyx technology changes the fabricproperties much, if at all. "You still getthe drape and feel of a fabric," Avlonisays ofEeontex. The conductive treat-ments can also be translucent enough toavoid much of a visual impact-though some versions of the Eeonyxcoating formulations are black.

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