North Carolina State Researchers Make an Upgrade to Wearable Thermoelectrics

February 09, 2020 by Luke James

Researchers at North Carolina State University (NCSU) have revealed their latest version of a device that can be used to convert body heat into power for wearable electronics.

The NCSU researchers described their flexible thermoelectric generator (or TEG) as using semiconductor elements connected electrically in a series using liquid-metal interconnects made from a non-toxic alloy of gallium and indium, EGaIn. This provided electrical conductivity and stretchability, allowing the entire device to be embedded within a stretchable silicone elastomer. 

In their research report, the NCSU researchers report that they have made significant enhancements to their TEG – a ‘flexible body heat harvester’ – that harvests heat energy from the human body to power wearable electronics. The underlying technology relies on the same principles governing rigid thermoelectric harvesters that convert heat to electrical energy.


The Self-healing Thermoelectric Material

According to Mehmet Ozturk of the NCSU team, the upgraded experimental device is “significantly better than other flexible devices reported to date and is approaching the efficiency of rigid devices, which is very encouraging,” because rigid devices have traditionally outperformed flexible devices when harvesting body heat. 

This is because the upgraded device uses an improved silicone elastomer that wraps around the EGaIn interconnects while still being built using almost the same architecture as the 2017 iteration, but improves the thermal engineering while increasing the density of the semiconductor elements that are used for converting heat into electricity. 

“The key here is using a high thermal conductivity silicone elastomer doped with graphene flakes and EGaIn,” Ozturk added. “Using this elastomer allowed us to boost the thermal conductivity – the rate of heat transfer – by six times, allowing improved lateral heat spreading. The flexible device reported in this paper is significantly better than other flexible devices reported to date and is approaching the efficiency of rigid devices, which is very encouraging.”


North Carolina State University's theromoelectric generator device.

The theromoelectric generator developed by North Carolina State University researchers capable of converting body heat into power for wearables. Image used courtesy of North Carolina State University.


Simplifying the Design Process for Manufacturers

Ozturk also stressed how the technology is beneficial for manufacturers because it eliminates the need for them to develop new flexible, thermoelectric materials. This is because their device uses the same semiconductor elements commonly found in rigid devices. He added that future research will focus on further improving the efficiency of these flexible devices. 

The device is ideal for use in a range of wearable devices, primarily consumer and health electronics, particularly those that need to be implanted. In the human body, there is plenty of heat that can be harvested by the TEG and used to power the batteries of flexible medical devices. This creates lots of potential for a new wave of internal sensors, treatment options, health monitors, and more which can be placed in areas previously unsuitable for rigid devices. 

Funding for the work comes from the NC State’s National Science Foundation-funded Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) Center under grant EEC1160483. The mission of the ASSIST Center is to create self-powered wearables capable of long-term multi-modal sensing without having to replace or charge the batteries.