The last few years have seen an explosive growth in wearable technology. From fabrics that interact with your devices to sunglasses that tint on demand, wearable electronics are set to take the world by storm. You can now add a stretchable loudspeaker to the list. Researchers have developed a skin-like device that can record and play back sound while attached to someone’s wrist.

Experts in acoustics and electronic engineering were brought together to find materials that could be used to create a flexible acoustic device that provides mechanical stability when stretched. Lead researcher Jeong Sook Ha from Korea University tells IFLScience that the design and method had to be “continuously modified” to create the stretchy gadget.

 

 

She says one of the most “challenging” aspects of the study was replacing the “rigid metal voice coil of dynamic acoustic device with an elastic liquid metal coil of Galinstan.” Researchers created this coil by injecting Galinstan – a liquid metal alloy – into a flexible polymer microchannel. Galinstan has excellent electrical conductivity, a low melting point, low vapor pressure, and low toxicity when compared with mercury, which Jeong Sook Ha says makes it a good fit for stretchable, wearable electronics.

Jeong Sook Ha explains that the operating principle is basically the same as that applied to earphones or microphones, driven using the interaction between a magnet and a current flowing coil.

The device was able record a human voice and a beeping alarm clock, and then play them back while attached to someone’s wrist. The study, published in Scientific Reports, demonstrates how the device was able to do this while being stretched repeatedly.

 

 

“Although flexible devices developed to date have contributed to the development of the wearable electronics, there are fundamental limits,” said Jeong Sook Ha.

She says the main problem with flexible devices is that many aren’t properly designed to cope with a surface like human skin. These devices have to deal with a range of motions, such as stretching, bending and twisting.

Jeong Sook Ha suggests there are “many body-attachable and wearable acoustic applications” to the stretchable acoustic device. These include a wearable health monitoring device for measuring heart rate, hearing aids and an information notification device that is attached to your body.

The researchers will continue working to optimize the structural design of their device as its acoustic performance is not good enough to be commercialized at this stage. Additionally, they hope to make the device thinner and smaller.