Fabric Microphone Converts Audio Into Electrical Signals

Engineers from MIT and the Rhode Island School of Design have developed an acoustic fabric that acts similar to a microphone – converting sound into mechanical vibrations, then into electrical signals. All fabrics vibrate in response to sound, only they do so on the nanometer scale and are often far too small to be sensed. To capture those imperceptible signals, the researchers created a flexible fiber that bends with fabric, similar to seaweed floating in the ocean.

Designed from a piezoelectric material, the fabric produces an electrical signal when bent or mechanically deformed. The fabric is sensitive enough to pick up decibels ranging from sound in a public library to heavy road traffic and can even determine the direction of sounds like handclaps. Moreover, the fabric is sensitive enough to detect subtle heartbeats from the wearer and can even act as speakers to generate sounds, including spoken words.

Inspired by the human auditory system, the team made a layered block of materials (known as a perform) made from a piezoelectric layer and others to boost the vibrations in response to soundwaves. The resulting perform is about as thick as a marker and was heated and stretched like taffy into 40-meter-long fibers. They then tested its sound sensitivity by attaching it to a mylar sheet and measuring the vibration conducted from a nearby speaker using a laser. The vibrations varied in decibels and generated an electric current that was proportional to the sound being played. The engineers then wove the fiber with conventional yarns to create machine-washable panels (comparable to denim), sewed them onto the back of a shirt and tested its directional sound capabilities. They discovered it was able to detect the angle of the sound from a distance of three meters away.

They also learned it could detect heartbeats when worn on the front of a shirt. What’s more, they flipped the fabric’s function and introduced a series of recorded spoken words and found the fabric converted the signals into audible vibrations that act as a speaker. The engineers state that their new material could be used for a new hearing aid, clothes that communicate and track vital signs. It could also be used as spacecraft skin that can listen to the universe, buildings that can detect strains and cracks and even made into a net that can monitor the oceans.