Thin, flexible materials have made a variety of wearable electronic devices possible. However, acoustic devices, including sensors, hearing aids, and portable music players, remain a challenge.
Jeong Sook Ha, Korea University, Seoul, and colleagues have developed a device that records and plays back sounds, even as it is being stretched and deformed. The device uses a neodymium magnet interacting with a coil made of liquid Galinstan alloy (gallium, indium, and tin). Galinstan, which melts well below room temperature, was injected into a spiral-shaped microchannel made from a blend of polydimethylsiloxane and Ecoflex (a biodegradable polyester). A permanent neodymium magnet was attached in the center of the coil.
The researchers successfully recorded and played back a human voice and a beeping alarm clock as the device was being deformed. They used the device as a microphone connected to the audio input port of a desktop computer, and as a loudspeaker to play back sounds from the computer. The device exhibits stable acoustic performance in the audible frequency range from 20 Hz to 20 KHz. There was no detectable degradation of the sound even after 2000 repetitive applications of a 50 % uniaxial strain.
- Stretchable Loudspeaker using Liquid Metal Microchannel,
Sang Woo Jin, Jeongwon Park, Soo Yeong Hong, Heun Park, Yu Ra Jeong, Junhong Park, Sang-Soo Lee, Jeong Sook Ha,
Sci. Rep. 2015.