Going Strapless

Serious runners and fitness freaks swear by heart rate monitoring, but they sometimes chafe, literally, at having to wear the hard plastic chest bands that house the monitor's electrode and transmitter. Textronics Inc. recently found a way to make heart rate monitoring more comfortable — at least for women.

The company's new Numetrex Sports Bra incorporates a conductive textile that turns the bra's rib cage strap into an electrode that picks up the heart's electrical signals. "The functionality is the same as a stand-alone heart rate monitor band," says Stacey Burr, Textronic's president.

Yet unlike traditional monitor bands, which encase the electrode in a hard plastic shell, the conductive textile is a flexible, seamless part of this nylon and Lycra bra. "If you feel the garment, you wouldn't be able to tell where the conductive area is," says Burr, who started her career as a polymer engineer. The only "hard" part of the bra is a small, snap-on transmitter that sends heart rate data to a third-party heart monitor watch, such as those made by Polar.

Textronics has performed pressure mapping studies that compare the bra to the usual plastic heart rate monitor bands. "We found that the bra applies four to five times less pressure than the band," Burr reports.

OK, so the bra is comfortable. So why should Design News readers, more than 98 percent of whom are men, care? Well, for one thing, Textronics has a man's running shirt with heart rate monitoring in development. Burr reports that the company is working out ways to keep a small zone of the shirt in contact with the body at all times — something the bra does naturally.

But even engineers who have no intention of leaving their cubicles for a run may want to take notice of electro-functional fabrics. Textronics can tailor its technology to different application requirements with textiles that can warm, illuminate, conduct and sense.

Textronics and other suppliers create these textiles by incorporating functional materials directly into the yarn. For example, to create a conductive fabric, the company might integrate fine copper wires into a yarn. "That's a conductive textile at its most basic level," says Burr. She notes that the Numetrex bra actually uses a proprietary conductive material she describes only as having "high, metal-like conductivity." And she adds that Textronics is experimenting with intrinsically conductive polymers, so the conductive systems don't necessarily have to rely on metals.

Of all the potential applications for electro-activated textiles, sensors may be the most promising. "What we're able to do particularly well is make sensors more flexible and elastic," Burr says. Indeed, the textiles that Textronics works with have elongations of several hundred percent, though the company offers less stretchy materials too.

The upshot of all the stretch is sensing systems, potentially well suited to motion and vibration monitoring, says Burr. She adds that Textronics has also created fabrics that can sense pressure, strain and temperature. What's more, the company has come up with a concept for a respiratory monitor that uses optical sensing. "The possibilities are endless," she says.

One challenge for engineers, though, is to become more fabric-savvy. Interfacing textile-based systems with rigid electronics requires different interconnect approaches. "We spend a lot of time educating electrical engineers who tend not to know that much about fabrics," she says.

For more discussion on electro-active fabrics join our Electronics Forum at: http://rbi.ims.ca/4922-534