This fabric can hear your heartbeat
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Someday our clothing may eavesdrop on the soundtrack of our lives, capturing the noises around and inside us.
A new fiber acts as a microphone — picking up speech, rustling leaves and chirping birds — and turns those acoustic signals into electrical ones. Woven into a fabric, the material can even hear handclaps and faint sounds, such as its wearer’s heartbeat, researchers report March 16 in Nature. Such fabrics could provide a comfortable, nonintrusive — even fashionable — way to monitor body functions or aid with hearing.
Acoustic fabrics have existed for perhaps hundreds of years, but they’re used to dampen sound, says Wei Yan, a materials scientist at Nanyang Technological University in Singapore. Fabric as a microphone is “totally a different concept,” says Yan, who worked on the fabric while at MIT.
Yan and his colleagues were inspired by the human eardrum. Sound waves cause vibrations in the eardrum, which are converted to electrical signals by the cochlea. “It turns out that this eardrum is made of fibers,” says Yoel Fink, a materials scientist at MIT. In the eardrum’s inner layers, collagen fibers radiate from the center, while others form concentric rings. The crisscrossing fibers play a role in hearing and look similar to the fabrics people weave, Fink says.
Analogous to what’s happening in an eardrum, sound vibrates fabric at the nanoscale. In the new fabric, cotton fibers and others of a somewhat stiff material called Twaron efficiently convert incoming sound to vibrations. Woven together with these threads is a single fiber that contains a blend of piezoelectric materials, which produce a voltage when pressed or bent (SN: 8/22/17). The buckling and bending of the piezoelectric-containing fiber create electrical signals that can be sent through a tiny circuit board to a device that reads and records the voltage.
The fabric microphone is sensitive to a range of noise levels, from a quiet library to heavy traffic, the team reports, although it is continuing to investigate what signal processing is needed to detangle target sounds from ambient noise. Integrated into clothing, this sound-sensing fabric feels like regular fabric, Yan says. And it continued to work as a microphone after washing it 10 times.
