13 July 2010

Acoustic fabric functions as speaker and microphone

by Kate Melville

MIT researchers have announced a new milestone on the path to functional fibers: acoustic threads that can both detect and produce sound. Applications touted include clothes that function as sensitive microphones, for capturing speech or monitoring bodily functions.

In Nature Materials, MIT scientist Yoel Fink explains that the heart of the new acoustic fibers is a plastic commonly used in microphones. In a conventional piezoelectric microphone, the electric field is generated by metal electrodes. But in a fiber microphone, the manufacturing process would cause metal electrodes to lose their shape. So the researchers instead used a conducting plastic that contains graphite. After the fiber has been drawn, the researchers align all the piezoelectric molecules in the same direction using a powerful electric field.

Despite the delicate balance required by the manufacturing process, the researchers were able to build functioning fibers in the lab. "You can actually hear them, these fibers," says co-researcher Noémie Chocat. "If you connected them to a power supply and applied a sinusoidal current then it would vibrate. And if you make it vibrate at audible frequencies and put it close to your ear, you could actually hear different notes or sounds coming out of it."

In addition to wearable microphones and biological sensors, applications of the fibers could include loose nets that monitor the flow of water in the ocean and large-area sonar imaging systems with much higher resolutions: A fabric woven from acoustic fibers would provide the equivalent of millions of tiny acoustic sensors.

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Source: Massachusetts Institute of Technology