The goal of the project is to make wearable technologies that can be used for long-term health monitoring

The goal of the project is to make wearable technologies that can be used for long-term health monitoring

US researchers have developed a new lightweight, wearable technology that converts body heat to electricity and could be incorporated into garments such as T-shirts.

According to the team of scientists at North Carolina State University, the experimental thermoelectric generators conform to the shape of the body, and can generate far more electricity than previous lightweight heat harvesting technologies.

The new design features a layer of thermally conductive material that rests on the skin and spreads out the heat. The conductive material is topped with a polymer layer that prevents the heat from dissipating through to the outside air and forces the body heat to pass through a centrally-located thermoelectric generator (TEG) that is 1cm2. Heat that is not converted into electricity passes through the TEG into an outer layer of thermally conductive material, which rapidly dissipates the heat. The entire system is 2mm thin, and flexible.

"Wearable thermoelectric generators (TEGs) generate electricity by making use of the temperature differential between your body and the ambient air," explains Daryoosh Vashaee, an associate professor of electrical and computer engineering at NC State and author of a paper on the work.

"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 centimetre 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."

The goal of the project 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, Vashaee adds.

"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."

The researchers found the upper arm was the optimal location for heat harvesting. Meanwhile, wearing the band on the chest limited air flow and heat dissipation.

After incorporating the TEG into T-shirts, the researchers found that although less efficient than the upper arm bands, they are still capable of generating 6 µW/cm2 – or as much as 16 µW/cm2 if a person is running.

Separate research by a team of scientists at Georgia Institute of Technology has developed a fabric to "harvest" electricity from the sun and movement that could then be used to power devices such as smart phones.

New fabric harvests energy to power devices