Materials science: A stretchable loudspeaker

A stretchable acoustic device that can operate as a loudspeaker and microphone is described in Scientific Reports this week. The device, which can record and play back sound while attached to the wrist, has the ability to survive stretching without a loss of performance.

Recent developments have led to the production of flexible acoustic devices. However, finding materials that provide mechanical stability when stretched has slowed developments in this field. Jeong Sook Ha and colleagues created a stretchable acoustic device by replacing the conventional rigid metal coil with a deformable liquid metal coil of Galinstan, a liquid metal alloy. The loudspeaker element of the device was driven by the interaction between the liquid metal coil and a permanent neodymium magnet.

The authors were able to record sounds such as the human voice and a beeping alarm clock and play them back while the device was attached to the wrist or was being stretched by hand. They found that the device could perform across the frequency range of human hearing (20 Hz to 20 kHz) upon repeated cycles of mechanical deformation.