Arm band technology converts body heat to energy

Researchers at South Korea's KAIST university have developed a flexible thermoelectric generator that can convert body heat to power.

What if you never had to charge your wearable tech — because it was able to harvest your body heat to run? That could soon be possible, thanks to a device developed by researchers at KAIST, led by electrical engineering Professor Byung Jin Cho — and not just for wristbands, but for heart monitors, smart glasses and other wearable tech.

The device they have created is a thermoelectric (TE) generator embedded in glass fabric, which solves two problems with previously developed wearable TE generators: organic-based TE generators embedded in polymers are flexible, but with a low power output; inorganic-based TE generators produce high power, but are rigid and clunky.

The glass fabric created by Professor Cho's team is so flexible it has a bending radius as low as 20 millimetres, but the generator maintains a high power output. The team created it by synthesising pastes of thermoelectric materials, bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3). These pastes were then applied to the glass fabric using a screen printing technique. They permeated the mesh of the fabric and formed films of TE materials several hundred microns thick, evenly applied and carefully spaced.

This eliminates the need for thick external substrates such as ceramic or alumina, minimising thermal energy lost in the casing, while maximising power output. A generator sized 10 x 10 centimetres can produce around 40 milliwatts of power based on a skin temperature of 31 degrees Celsius.

"For our case, the glass fabric itself serves as the upper and lower substrates of a TE generator, keeping the inorganic TE materials in between. This is quite a revolutionary approach to design a generator. In so doing, we were able to significantly reduce the weight of our generator (~0.13g/cm2), which is an essential element for wearable electronics," Professor Cho explained.

"Our technology presents an easy and simple way of fabricating an extremely flexible, light, and high-performance TE generator. We expect that this technology will find further applications in scale-up systems such as automobiles, factories, aircrafts, and vessels where we see abundant thermal energy being wasted."

The paper, "Wearable Thermoelectric Generator Fabricated on Glass Fabric", was published in the journal Energy & Environmental Science, and will be available free online until 15 May.