Wearable electronics could someday be powered by body heat

wearable thermoelectric generator
© North Carolina State University

A new lightweight thermoelectric generator has been developed at NC State, which may be able to power small health sensors or other small wearable devices.

With the increasing adoption of mobile devices, which range from consumer electronics such as smart watches and fitness trackers to health monitors and other sensors, comes an increase in the need for better mobile power supplies, and although battery technology is improving (other than, you know, those exploding batteries), it seems equally important to continue to develop other methods of harvesting energy for mobile devices, such as this hybrid power textile.

One potential source of energy could be the heat of the human body, or more accurately, the difference in temperature between the body and the ambient air surrounding it, and while heat harvesting isn't a brand new technology, researchers at North Carolina State University have developed what they say is a much lighter and more efficient wearable thermoelectric generator (TEG) that can generate "far more electricity" than previous versions.

Previous approaches either made use of heat sinks – which are heavy, stiff and bulky – or were able to generate only one microwatt or less of power per centimeter squared (µW/cm2). Our technology generates up to 20 µW/cm2 and doesn’t use a heat sink, making it lighter and much more comfortable." - Daryoosh Vashaee, an associate professor of electrical and computer engineering at NC State and corresponding author of a paper on the work

The new wearable TEG design from the team is built with a layer of thermally conductive material, which rests directly on the skin and spreads the heat uniformly across itself, and then a polymer layer on top of it which keeps the heat from immediately dissipating away from the body, which forces the body heat to pass through a small TEG to be converted to electricity. Excess heat that is not used in the conversion process is passed through the device onto an outer layer of material, which allows the heat to dissipate away from the body. The new TEG system is just 2 millimeters thick, and is flexible, which lends itself well to being worn on different areas of the body without being bulky or disruptive to regular activities.

According to the team, testing of the device on both the arm and the chest of users determined that the upper arm was the best location for harvesting heat with the TEG. Mounting the TEG on the chest, where it would normally be covered by a shirt, limited its efficiency, but the team also tested the device when incorporated into a T-shirt, where it was found to be able to generate up to 16 µW/cm2 if the wearer was running.

"T-shirt TEGs are certainly viable for powering wearable technologies, but they’re just not as efficient as the upper arm bands.” - Vashaee

The project, which is part of the National Science Foundation’s Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) at NC State, could have implications for asthma sufferers or those with heart conditions, as one of the goals of the program is to make monitoring devices that don’t rely on batteries. By building better TEGs, the team is helping to move that goal forward, and because the devices can be scaled up, a mobile power supply running on body heat is that much closer to becoming a viable option.

The team published its findings in the journal Applied Energy under the title "Wearable thermoelectric generators for human body heat harvesting."

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