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These tiny, stretchy speakers and microphones let your skin play music

If you’re prone to forgetting your headphones, new wearable technology that could turn your skin into a speaker should be music to your ears. Created in part to help the hearing and speech impaired, the new “smart skin” could be embedded into the ears—or into a patch on the throat. A similar device, described in the same study, acts as a microphone, which can be connected to smartphones and computers to unlock voice-activated security systems.

To build the speakers and the microphone, which are thinner than a temporary tattoo, the researchers needed to design electronics flexible enough to stretch and bend with the skin, without losing their capacity to conduct electricity and heat—both necessary to transmit audio signals.

After testing different materials, the scientists settled on grids of tiny silver wires coated with polymer layers, which were stretchy, transparent, and capable of conducting sound signals.

After receiving an electric audio signal from a music player, the tiny loudspeaker heats up the wire grid to about 33°C, which replicates the sound pattern by changing the pressure of the surrounding air. Our ears pick up these changes in air pressure as sound waves.

The microphone operates in reverse, converting speech sound waves back into an electric signal, which can then be stored and played back by a smartphone or computer. It can detect sound waves coming from the mouth, but it can also recognize words simply from the rumbling of the vocal cords through the skin, the team reports today in Science Advances.

The researchers tested the microphone by asking four people to unlock a smartphone with voice-recognition software; only one of the subjects was the registered user. Over 10 trials, the system was able to recognize the correct voice more than 98% of the time.

The next step, say the researchers, is to improve the sound quality and volume of the speakers, which are quiet and tinny, as well as the accuracy of the microphone in detecting speech and distinguishing between different voices. They also want to come up with better materials for mass manufacturing. Until the skin speakers hit the market, make sure to grab those headphones on your way out the door.