A fabric that listens

A fabric capable of tuning in to the sounds around it has been developed at Massachussets Institue of Technology (MIT).

Flat fabric can ripple with waves when exposed to sound, much like the surface of water. These waves are typically too small to detect, but a special fibre woven into the fabric can convert these small waves into electrical signals.

"Fabrics contain the soundtrack of our lives," says Professor Yoel Fink from MIT. Fabrics are deeply connected to our everyday lives, from the clothes off our backs to upholstery and other home comforts. Giving these fabrics additional functionality can greatly benefit our day to day activities.

Sound is simply a pressure wave, typically detected by our ears. When a pressure wave hits a fabric, it causes ripples in the fabric. But these are too small for us to feel or see. 

Taking inspiration from a human ear where fibres play important roles in converting pressure waves to electrical signals, the team from MIT developed a fibre to help detect sound ripples in a fabric.

The fibre needs to be flexible in order to bend with the sound waves created in the fabric. In addition, the fibre needs to produce electrical signals when bent to collect the sounds. To do this, they encapsulated a piezoelectric material in a rubbery material. Piezoelectric (from Greek piezein - to squeeze) is a materials property that means when the matrial is deformed, it creates an electric charge in the material.

The fibre is then woven into a piece of fabric. The researchers were able to demonstrate that their fabric can detect sounds such as clapping. They can even detect which direction the sound came from if multiple fibres are used. 

Not only is the fabric functional, they also ensured that the fibre was easy to manufacture. The functional fabric still behaved like a fabric and is even machine washable. This means the technology is viable for mass production and can eventually become ubiquitous.

According to Fink, a four-step approach to a future of functional fabrics is needed, comprising fibres with specific functions and properties such as piezoelectrics or fibre batteries; combining the fibres into a fabric; translating the electrical signals collected by the fabric into useful information, such as a human voice and words; and designing "apps" to utilise the functionalites. For example, being able to pick up sounds clearly if you are in a noisy environment, or listening to the heartbeat of a fetus if you are pregnant.

The possibilities are endless, he says.