An uncommon thread

LAS VEGAS in January is the place to spot the latest trends in consumer electronics. The one that grabbed the attention of most people at the 2014 CES show were the wearables. These are gadgets that you put on, from all sorts of spectacles with built-in cameras and screens, like Google Glass, to wrist bands and watches that can monitor your heart rate or relay text messages. There is even jewellery that can warn you of too much exposure to the desert sun.

Fashionistas, however, were not impressed. These gizmos were far too clunky and geeky to be worn by anyone with dress sense, one columnist complained.

That is about to change. Developments in the use of conductive fibres mean fabric itself can now become an electronic device, allowing wearables to be incorporated into the most stylish clothing. And the fibres, being much lighter than metal wires, will enhance lots of other products, too.

Most conductive fibres are so flexible they do not crack or snap if repeatedly bent, unlike metal wires. This means they can be fed into a loom or embroidered directly onto cloth that can be worn and washed as normal. With costs falling and use increasing, the threads are a rapidly growing business, says Hugo Trux, head of the Conductive Fibres Manufacturing Council (CFMC), an American trade group.

Using fibres that conduct electricity opens up all sorts of new design possibilities. For instance, Intelligent Textiles, a company in London, has worked with the British and Canadian armed forces to produce combat fatigues with pathways of conductive fibres to deliver power to the increasing amount of equipment which soldiers now wear for combat. The idea is to do away with the “Christmas-tree effect” of battle dress being swathed in cables and batteries, says Stan Swallow, a director of the company. Instead, power from a single battery-pack can be clipped to a belt or an armoured vest and channelled to any equipment the soldier is wearing.

Smart shirts

It is not just power leads that can be incorporated into fabrics, but electronic devices as well. Colin Cork and his colleagues at the Advanced Textiles Research Group at Nottingham Trent University in Britain have embroidered antennae onto shirts using silver-coated thread. In some cases, this is virtually impossible to see. The embroidered antennae can be used by devices worn by the user to transmit and receive radio signals or to boost the device’s own transmission range.

Some companies want to use the idea to conceal radio-frequency identification (RFID) tags in valuable fashion goods. This would be possible even in lightweight garments. A woven RFID tag could be read by a wireless reader (and, no doubt, eventually by a smartphone app too—which could lead to some embarrassment when someone scans your new Prada number and discovers it’s a knock-off).

Researchers have also used conductive yarn to embroider alphanumeric and musical keyboards into fabric. Touching a particular key dissipates an electrical charge which can be detected by an embedded processor. Often the idea is to use the electronics contained in the garment in tandem with a traditional clip-on device.

With a glance at their smartphone, wearers will see statistics on, among other things, their “Zen index”

Adidas, a German producer of sportswear, has started knitting conductive fibres into stretchy garments to produce “textile electrodes”. These are only a few square centimetres in size and can pick up signals from the heart and other muscles. The data gathered by the electrodes are transmitted through the garment to a small gadget that is snapped into a shirt or sports top (as pictured above). This, in turn, passes them wirelessly to a user’s mobile phone for processing and display.

Textile electrodes are almost undetectable to the touch and do not need any sticky goop to make them work when next to the skin (although sweat does improve signal quality). The data can be transmitted directly by an athlete to his coach, or by a patient to a doctor, says Stacey Burr, head of wearable electronics for Adidas. Nor is the technology particularly expensive. In Germany, some of the company’s “sensor garments” sell for less than €60 ($81).

Adidas is now designing workout tops that use elastic conductive fibres to measure the wearer’s breathing. A snap-in device feeds a small electric charge into a ring of conductive fibres that encircles the chest. Because the conductivity of the fibres decreases slightly upon stretching, the garment can calculate the quantity of air that has entered the lungs. Adidas will initially offer this to athletes who want detailed performance statistics, says Ms Burr. The system, known as RIP for respiratory inductive plethysmography, could be integrated with additional kit for medical use.

Plenty of other body-sensing clothing is being developed. At the Fraunhofer Institute in Berlin, researchers have come up with textile electrodes that measure the electrical activity of the large trapezius muscle in the shoulder and neck. The system can distinguish between physical and psychological stress; the latter being identified by unnecessarily tightened shoulders. Such clothing could inform a wearer when it is best to pause during exercise. Attaching conventional electrodes to someone’s body for the same purpose can itself cause them stress, says Torsten Linz, a member of the research team.

Researchers at Virginia Tech use conductive fabric to shuttle battery power and data to and from miniature gyroscopes and compasses fastened to shirt cuffs and other bits of clothing. The idea, says Tom Martin, a professor at the university, is to log and transmit an elderly patient’s movements to a therapist or doctor. The computerised analysis is not yet perfect, admits Dr Martin. The system may, for example, determine that a patient brushed her teeth when in fact she brushed her hair.

Conductive fibres will have a broad “lifestyle” appeal, reckons Joanna Berzowska, head of electronic textiles at OMsignal, a Montreal startup. The company plans to start selling “smartwear that feels like everyday wear”. Its garments will use silver- and steel-blended yarns to report on muscle activity. With a glance at their smartphone, wearers will see statistics on, among other things, their “Zen index”.

Besides adding functionality to clothing, conductive fibres have huge potential as a weight-saving material. Every kilo removed from a typical airliner reduces its lifetime fuel cost by roughly $2,200, reckons the CFMC trade group. Aircraft could be made a lot lighter by replacing metal wiring—which for a big plane can amount to some 320km of cable and braided shielding, which prevents signal interference—with natural and synthetic fibres treated to conduct electricity.

One such fibre, a cottony yarn branded ARACON, is being used by Airbus, Boeing, Bombardier and Embraer in some of their aircraft. ARACON was developed by DuPont as an alternative to its Kevlar fibre, which is used in things ranging from bulletproof vests to drum heads. Micro-Coax, a firm in Pennsylvania, makes ARACON by coating the synthetic fibres of Kevlar with copper, nickel and silver. The resulting yarn is not just lighter than metal wire, but also stronger and suppler, so it can follow more tortured pathways when wiring up complex machines like aircraft.

Into orbit

ARACON has been expensive to make, so its use was essentially limited to spacecraft, where losing a kilo cuts the cost of a launch by about $25,000. However, the brisk orders and a $2m investment in the manufacturing process are now bringing the price down. In the past year alone it fell by about half, says Ron Souders, Micro-Coax’s technical expert.

The engineering potential of most conventional metal wire peaked a decade or two ago, says Al Abel, a former executive at Syscom Advanced Materials, a maker of conductive fibres in Columbus, Ohio, but advances in conductive fibres are redefining how electrical wiring can be used. Eventually, even power-transmission lines could be replaced with aluminium- or copper-coated brawny synthetic fibres such as Zylon, which is already used to protect the cockpits of Formula 1 racing cars. Such fibres could make power lines a third or so lighter and at least several times stronger, reckons Mr Abel. That means far fewer would break in storms.

There are many different ways used by companies to make conductive fibres. Textiles can simply be intertwined with filaments of stainless steel or other metals, or they can be dipped in liquid metals such as aluminium and magnesium. The surface of a fibre can be melted until it is sticky enough to capture sprayed particles of carbon. A particularly tricky process involves dipping fibre into sulphuric acid to create toeholds that, after being soaked in palladium salt and a nickel-plating solution, become encrusted with nickel crystals. The now-conductive fibre is then rigged to a charged copper ingot in a bath, with the result that copper particles electroplate its surface. Mr Abel, who helped design this process at Syscom, left the firm to develop a system that instead uses an ion beam to drive metal particles into fibre like “billions of tiny bullets”.

Rarely is much metal needed. Copper fibre, for example, may contain just a third of the copper in the solid wire it replaces. Fibres of stainless steel made by R.STAT, a French firm, are under 12 microns in diameter—less than half the thickness of a human hair. It is so soft to handle that people cannot tell it is made from steel, says Pascal Peninon, an R.STAT manager.

More exotic applications are emerging. CanShielding, an Ontario firm, is developing lightweight carbon- and silver-fibre aprons to protect x-ray technicians. The garb is more comfortable than the heavy gear the technicians now don. The company is also developing a fabric that partially absorbs radar signals.

Smart underwear is likely to be a hot fashion item in the future. An American lingerie firm has shown interest in a textile called Fabcell that uses liquid-crystal inks to change colour when its fibres are warmed by a battery, says its inventor, Akira Wakita of Keio University in Japan. SwicoFil, a Swiss company, makes a range of conductive fibres, including a gold-coated thread for Rococo Dessous, which produces luxury lingerie. The catwalks of London, Milan, New York and Paris are bound to get a lot more interesting.