MIT researchers develop fabric that converts sounds into signals

April 19, 2022 - United States Of America

Engineers from the Massachusetts Institute of Technology (MIT) and collaborators at Rhode Island School of Design have designed a fabric that works like a microphone, converting sound first into mechanical vibrations, then into electrical signals. Inspired by the human ear, a new acoustic fabric converts audible sounds into electrical signals.

All fabrics vibrate in response to audible sounds, though these vibrations are on the scale of nanometers — far too small to ordinarily be sensed. To capture these imperceptible signals, the researchers created a flexible fibre that, when woven into a fabric, bends with the fabric like seaweed on the ocean’s surface, MIT said in a press release.

The fibre is designed from a “piezoelectric” material that produces an electrical signal when bent or mechanically deformed, providing a means for the fabric to convert sound vibrations into electrical signals.

The fabric can capture sounds ranging in decibel from a quiet library to heavy road traffic, and determine the precise direction of sudden sounds like handclaps. When woven into a shirt’s lining, the fabric can detect a wearer’s subtle heartbeat features. The fibres can also be made to generate sound, such as a recording of spoken words that another fabric can detect. Lead author Wei Yan, who helped develop the fiber as an MIT postdoc, sees many uses for fabrics that hear.

“Wearing an acoustic garment, you might talk through it to answer phone calls and communicate with others,” said Yan, who is now an assistant professor at the Nanyang Technological University in Singapore. “In addition, this fabric can imperceptibly interface with the human skin, enabling wearers to monitor their heart and respiratory condition in a comfortable, continuous, real-time, and long-term manner.”

Yan’s co-authors include Grace Noel, Gabriel Loke, Tural Khudiyev, Juliette Marion, Juliana Cherston, Atharva Sahasrabudhe, Joao Wilbert, Irmandy Wicaksono, and professors John Joannopoulos and Yoel Fink at MIT, along with Anais Missakian and Elizabeth Meiklejohn at Rhode Island School of Design (RISD), Lei Zhu from Case Western Reserve University, Chu Ma from the University of Wisconsin at Madison, and Reed Hoyt of the US Army Research Institute of Environmental Medicine.

Inspired by the human auditory system, the team sought to create a fabric “ear” that would be soft, durable, comfortable, and able to detect sound. Their research led to two important discoveries: Such a fabric would have to incorporate stiff, or “high-modulus,” fibres to effectively convert sound waves into vibrations. And, the team would have to design a fibre that could bend with the fabric and produce an electrical output in the process.

With these guidelines in mind, the team developed a layered block of materials called a preform, made from a piezoelectric layer as well as ingredients to enhance the material’s vibrations in response to sound waves. The resulting preform, about the size of a thick marker, was then heated and pulled like taffy into thin, 40-meter-long fibres, the release added.

The researchers tested the fibre’s sensitivity to sound by attaching it to a suspended sheet of mylar. They used a laser to measure the vibration of the sheet — and by extension, the fibre — in response to sound played through a nearby speaker. The sound varied in decibel between a quiet library and heavy road traffic. In response, the fiber vibrated and generated an electric current proportional to the sound played.