Silicone elastomer powers wearable-device advance

Raleigh, North Carolina – Modifications to a silicone elastomer compound have enabled US researchers to improve the ability of flexible wearable devices to harvest heat-energy from the human body.

The team at North Carolina State University (NCSU) have reported significant progress in preventing heat leakage from body-heat harvesters they have been seeking to optimise since 2017. 

A particular target for the technology is to power smart watches that measure heart rate, blood oxygen, glucose and other health parameters – eliminating the need for batteries. 

Originally, the devices employed semiconductor elements that were connected electrically in series using liquid-metal interconnects embedded in a stretchable silicone elastomer. 

The interconnects are made of EGaIn, an alloy of gallium and indium that exhibits metal-like electrical conductivity and stretchability. 

Energy delivery was subsequently improved through the use of a higher thermal-conductivity version of the silicone elastomer used to encapsulate the EGaIn interconnects.

In the latest iteration, aerogel flakes have been added to the silicone to further optimise the elastomer’s thermal conductivity – tests show that this can halve ‘heat leakage’ through the elastomer. 

“The addition of aerogel stops the heat from leaking between the device’s thermoelectric ‘legs,’” according to Mehmet Ozturk, an NC State professor of electrical and computer engineering.

“The higher the heat leakage, the lower the temperature that develops across the device, which translates to lower output power,” explained Ozturk, adding that the devices now perform “an order of magnitude better” than the original units.