Material scientists from Japan have built a stretchy acoustic device that is capable of both recording and amplifying sound.
The device is said to be capable of recording different sounds and playing them back while attached to — and stretched around — a human wrist. It is also durable enough to survive repeated stretching without loss of performance. In video demos sounds including an alarm clock and the human voice were recorded and played back, even while the device was being stretched. In terms of frequency, the device can perform across the range of human hearing, from 20Hz and 20kHz.
The details of the invention are detailed in a paper published in the journal Scientific Reports, in which the authors suggest there could be applications in wearables or bio-printable devices.
“It is desirable to realise stretchable acoustic devices for body-attached applications such as sensing biological signals, hearing aids, and notification of information via sound,” the team writes.
To keep the device stretchy, and to ensure that it does not degrade over time, the speaker contains a liquid metal coil and a magnet. Compared to other approaches to making stretchable devices, including those that use graphene, ion-gel-based transparent loudspeakers or thermoacoustic loudspeakers, this new approach provides more mechanical stability primarily thanks to the alloy liquid metal, called Galinstan, contained within the coil. It possesses properties such as excellent conductivity, low vapour pressure and a low melting point. These combine to make Galinstan ideal for stretchable and wearable electronics.
“Successful demonstration of recording and playback of various types of sound under mechanical deformation shows the high applicability of our stretchable acoustic device as a body-attached acoustic device,” write the authors. “It is also expected that our invention would provide a promising solution to the research fields for the stretchable, wearable and bio-implantable acoustic electronics.”