Fibers That Can Hear and Sing Could Power Electronic Textiles

The clothing of the future could be more than just fashion. MIT researchers are working to develop fibers that can hear and produce sound, and someday those could take the form of wearable electronics.

“The ancients used clothes for the same reason that we do, which is thermal insulation and aesthetics,” Yoel Fink, associate professor of materials science and principal investigator at MIT’s Research Lab of Electronics, told Wired.com. “What we have done is start thinking how fibers go beyond that and change their properties.”

Fink and his team hope their latest research will result in fibers that can be fashioned into clothes capable of capturing speech, textiles that can measure blood flow in the capillaries or nets that can double as sound sensors.

“It’s a very significant breakthrough on the level of the material used and the structure that was fabricated,” says Ayman Abouraddy, a professor at the College of Optics & Photonics in the University of Central Florida.

“Line a whole wall with these fibers and you could get a very interesting surround-sound system,”� says Abouraddy, who isn’t involved in the research.

Fibers, whether they are for clothing or telecommunications, have always been static, incapable of doing more than one thing: Hold fabric together, or transmit optical signals, for instance. The key to electronic textiles is fiber that can change its properties over a wide range of frequencies, says Fink.

The acoustic fibers have been created from a plastic called polyvinylidene fluoride (PVDF) that’s commonly used in microphones. The researchers tweaked the plastic to ensure its molecules are lopsided so all the fluorine atoms line up on one side and hydrogen atoms on the other. This asymmetry of the molecules makes the plastic piezoelectric.

Piezoelectricity is the key property here that allows the fibers to react to a range of frequencies, giving them the ability to function as both a microphone and a speaker.

“The important aspect of it is maintaining the crystalline form in the fiber,” says Abouraddy. “Usually the crystal melts if it is heated sufficiently, which happens when the fibers are being manufactured, but the�new technique seems to have solved that problem.”

To manufacture the fibers, the piezoelectric molecules are all aligned in the same direction by applying an electric field that’s about 20 times as powerful as those that cause lightning during a thunderstorm.

So far, it has worked well enough that you can actually hear through the fibers. Researchers connected the fibers to a power supply and applied a current to make it vibrate at audible frequencies to generate sound.

The next major step will be to reduce the dimensions of the fiber so it can some day be woven into clothing.

“Right now the width of the fiber is around 2.5 mm, while in clothing today, the fibers are at around 50 microns,” says Abouraddy. “So they will have to reduce the width by a big magnitude.”

That’s one of the things that researchers will be working on over the next few years, says Fink. Eventually, he hopes, the manufacturing process will be perfected enough for the fibers to be affordable.

“Am I going to be able to sell this for a buck a meter in San Francisco soon? The answer is no,” says Fink. “But we should be able to get good economies of scale.”

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