Researchers at North Carolina State University developed a wearable that can harvest body heat to power devices with at least 20 times the efficiency of other methods, the school reported yesterday.
The study, published in the journal Applied Energy, was conducted at the National Science Foundation’s Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) at N.C. State.
Their experimental prototype is lightweight and flexible and conforms to the body. It can generate significantly more electricity than previous technology, the team reported.
The wearable is made of two layers – a thermally conductive layer that rests on skin to spread heat, and a layer of polymer that prevents heat from dissipating to outside air. The dual-layer system forces heat through a centrally-located thermoelectric generator.
“Wearable thermoelectric generators generate electricity by making use of the temperature differential between your body and the ambient air,” corresponding author Daryoosh Vashaee explained. “Previous approaches either made use of heat sinks – which are heavy, stiff and bulky – or were able to generate only 1 microwatt or less of power per centimeter squared (μW/cm<sub>2</sub>). Our technology generates up to 20μW/cm2 and doesn’t use a heat sink, making it lighter and much more comfortable.”
“In this prototype, the TEG is only 1cm<sub>2</sub>, but we can easily make it larger, depending on a device’s power needs,” Vashaee said.
The team also discovered that the wearable harvests the most heat when worn on the upper arm. They tried integrating the technology into a T-shirt, which generated some power, but not as much as when it was on the upper arm.
“The goal of [the N.C. State R&D shop] is to make wearable technologies that can be used for long-term health monitoring, such as devices that track heart health or monitor physical and environmental variables to predict and prevent asthma attacks,” according to Vashaee. “To do that, we want to make devices that don’t rely on batteries. And we think this design and prototype moves us much closer to making that a reality.”
