Using body heat to power wearables

If thermoelectric materials can convert low-grade heat into electricity, we may never need to charge wearable technology at home again.

At night, most of us plug in a jumble of wires and devices as we charge our smart watches, phones and fitness trackers. It’s a pile that’s unlikely to get any smaller as more and more wearable tech enters our lives. Manufacturers and futurists predict that these will soon be energy self-sufficient and that we’ll be free of their mess. But the question remains: how? At the moment the only major portable power sources are solar chargers, but these have significant limitations both indoors and after dark.

Kedar Hippalgaonkar, Jianwei Xu and their co-workers at A*STAR’s Institute of Materials Research and Engineering (IMRE) think they could soon use low-grade waste heat – think car exhaust or body heat – to power devices.

“An enormous amount of low-grade waste heat is being dumped into the environment”, says Hippalgaonkar. Converting this heat into electricity is a big opportunity that shouldn’t be missed.

High-temperature thermoelectric generators are already a key source of power for space instruments. The Mars rover, Curiosity, and the interstellar space probe, Voyager 2, harness long-lasting nuclear heat. The latter has been running on this type of power for more than 40 years. “Thermoelectric power generation is not a new idea,” explains Hippalgaonkar. “It’s been investigated since the 1950s and there’s been lots of research on new materials, but in the past most of the work focused on toxic, inorganic materials and applications with high temperatures of operation.”

Hippalgaonkar agrees that the proliferation of Internet of Things devices now brings with it a demand for non-toxic, portable power sources. Future body sensors and portable devices could be worn constantly if they harnessed body heat to be energy self-sufficient. “But to do that we need to develop suitable new thermoelectric materials that are efficient at lower temperatures, non-toxic and cheap to produce.”

The other major opportunity is to make use of any waste heat exiting through engine exhaust from cars, aeroplanes or ships, he adds. The electricity generated could then be fed back into the vehicle, lessening its environmental footprint.

A*STAR’s PHAROS project is focused on the materials that will make these thermoelectric generators possible. The five-year project started in 2016 and aims to find a material composition that is non-toxic and, ideally, Earth abundant (making it cheap), efficient, and easy to fabricate. To do this they are developing less toxic hybrid materials combining organic and inorganic elements, and they are pursuing those with potential for low temperature thermoelectric power generation.

Learn more: Putting body heat in the device game

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New thermoelectric materials could provide a low-cost option for converting heat energy into electricity