NC State Engineers Push Their Wearable Energy-Harvesting Tech to New Efficiency Highs

Engineers at North Carolina State University (NC State) have improved their wearable thermoelectric generator (TEG) that harvests body heat to power electronics, with the addition of aerogel flakes — reducing heat leakage from the soft silicone elastomer in which it's encased.

NC State first reported success with a new type of energy-harvesting system, a thermoelectric generator encased in flexible silicone, in 2017, using a non-toxic liquid metal alloy of gallium and indium to connect the thermoelectric 'legs' of the TEG elements and to provide a self-healing function. While functional, though, work still needed to be done on improving its efficiency.

Last year, an updated paper boasted of just such an efficiency gain, thanks to work on improving the thermal engineering and increasing the density of its semiconductor elements. Another gain: Doping the silicone elastomer with graphene flakes.

Now, the system has been boosted still further thanks to another item added to the elastomer mix: Aerogel. "The addition of aerogel stops the heat from leaking between the device's thermoelectric 'legs,'" explains Professor Mehmet Ozturk of the work. "The higher the heat leakage, the lower the temperature that develops across the device, which translates to lower output power."

"The flexible device reported in this paper is performing an order of magnitude better than the device we reported in 2017 and continues to approach the performance of rigid devices."

According to the team's testing, using an Arduino Mega development board, the improved device as worn on test subjects' wrists approaches 35µW/cm⁻² of energy generation at an air velocity equivalent to a walking speed — results which suggest, the engineers conclude, that they can be used as the main energy source for a range of low-power wearable electronics.

The team's work has been published in the journal njp Flexible Electronics under open-access terms.