Imagine a future where working up a sweat not only does your body good, but it’ll also keep your favorite devices humming. That’s the goal of researchers at North Carolina State University, where Daryoosh Vashaee and his team have developed a way to harvest body heat and turn it into electricity. Although similar technologies have been around for years, NC State said that its prototypes are lightweight, flexes to the body, and generate “far more” electricity than their predecessors. “Wearable thermoelectric generators generate electricity by making use of the temperature differential between your body and the ambient air,” Vashaee, an associate professor of electrical and computer engineering, and the corresponding author of a paper on the work, explained. “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.” The NC State version, he added, generates up to 20 µW/cm² and doesn’t use a heat sink, “making it lighter and much more comfortable.”
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Vashaee and company’s design features a layer of thermally conductive material that lies in conduct with the skin, plus a polymer layer that keeps the body heat contained. This setup, researchers said, feeds body heat through a centrally located thermoelectric generator, where any heat that isn’t converted into electricity dissipates into the outside air.
The entire system is only 2 millimeters thick, making it suitable for incorporating into T-shirts.
The entire system, they said, is only 2 millimeters thick, making it suitable for incorporating into thinner garments such as T-shirts.
For optimum energy-harvesting, however, Vashaee recommends a band, specifically one around the upper arm. It’s a more optimal location than, say, the wrist, where irregular contours limit the surface area of contact with the skin, or the chest, which is usually covered and has limited air flow.
“T-shirt TEGs are certainly viable for powering wearable technologies, but they’re just not as efficient as the upper arm bands,” Vashaee said.
Eventually, the technology could result in devices that monitor the wearer’s heart health or track physical and environmental factors to predict—and prevent—asthma attacks.
“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,” Vashaee added.