MIT scientists have developed fibers that can detect and produce sound, and say they could be used to produce clothes that act as microphones.
The new acoustic fibers are based on a plastic often used in microphones. By playing with the plastic's fluorine content, the researchers were able to ensure that its molecules remained lopsided — with fluorine atoms lined up on one side and hydrogen atoms on the other — creating a piezoelectric effect that survives the heating and drawing process.
In a conventional piezoelectric microphone, the electric field is generated by metal electrodes. But in a fiber microphone, the drawing process would cause metal electrodes to lose their shape. So the researchers instead used a conducting plastic that contains graphite.
"You can actually hear them, these fibers," says Noémie Chocat, a graduate student in the materials science department. "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 - fabric woven from acoustic fibers would provide the equivalent of millions of tiny acoustic sensors.
Zheng Wang, a research scientist in MIT's Research Lab of Electronics, points out that the same mechanism that allows piezoelectric devices to translate electricity into motion could also work in reverse. "Imagine a thread that can generate electricity when stretched," he says.
Ultimately, however, the researchers hope to combine the properties of their experimental fibers in a single fiber. Strong vibrations, for instance, could vary the optical properties of a reflecting fiber, enabling fabrics to communicate optically.