Stretchable Loudspeakers Developed

Engineers have created a stretchable acoustic device that functions as loudspeaker, microphone and recording device.

AsianScientist (Jul. 23, 2015) – A research group from Korea University has developed an acoustic device that is stretchable. Their device, described in Scientific Reports, can function as a loudspeaker, microphone and audio recording device even after being subjected to a stress test of 2,000 stretches.

Portable audio devices have gone a long way from the early gramophone cases to walkman players to MP3 players. These devices become more intuitive and integrated into our lives as technology advances. Now, it may be possible in the near future to have a wearable audio device based on the advancement made by Professor Ha Jeong Sook and her team.

Ha and colleagues have been conducting research stretchable devices including sensors and energy storage devices. In their studies, they found liquid metals—like Galinstan,­ a metal alloy with a melting point of ­19 degree Celsius—to be particularly suitable for stretchable devices.

The idea to use Galinstan to create stretchable acoustic device came from Ha’s graduate student and first author of the paper, Jin Sang Woo. To fabricate the stretchable acoustic device, the authors designed a clear, stretchable polymer coiled mold, where they microinjected the fluid metal into the mold. They then placed a magnet and other accessory components into the mold to complete the acoustic device on the liquid metal coil.

“[The] operating principle of our stretchable acoustic device is basically the same as that applied to the earphone or microphone, typically driven in a dynamic way using the interaction between a magnet and a current flowing coil,” Ha told Asian Scientist Magazine.

“In this work, we replaced rigid metal voice coil of dynamic acoustic device with an elastic liquid metal coil of Galinstan. Therefore, in this case, liquid metal coil is vibrated by a force formed by the current and the magnetic field.”

The authors also managed to show that this device can function as a audio recorder with playback functions when attached and stretched on the human wrist. Although flexible devices have been developed, there are fundamental limitations as they may not work properly on non­planar surfaces like the human skin. In contrast, Ha’s device was amenable to body motions like stretching, bending and twisting, while staying functional.

Specific applications of this audio device are body­ attached, wearable acoustic applications such as sensing biological signals, like heart rate, and hearing aids. As much as this finding paves a way for future wearable technologies, improvements to the device is still required.

“I think the most important thing is to optimize the structural design of our device. Although we showed that the stretchable loudspeaker is operating under mechanical deformation, the acoustic performance of the device is not good enough to be commercialized in this stage,” said Ha.

In addition, the authors hope to develop thinner devices with a stretchable magnet.

The article can be found at: Jin et al. (2015) Stretchable Loudspeaker Using Liquid Metal Microchannel.


Copyright: Asian Scientist Magazine; Photo: Ha Jeong Sook.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Ying Ying completed her PhD in neurobiology at the University of Basel, where she studied the role of bone morphogenetic protein in structural plasticity of neurons.

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