In order for Health Tech wearables to become widely adopted, they must be able to go about their duties with a minimum of attention from their users. Having to recharge a device every night is not convenient, especially when you compare it to a typical $25 wristwatch that can run for three years or more on a single coin-style battery. One solution is to harvest energy from the ambient environment — heat, light, radio waves, motion, sound, vibrations — that can be converted into electricity to provide some or all of the device’s power requirements.

One of the most intriguing sources is heat. Traditionally, a relatively large temperature difference is needed to produce a useful amount of power, but recent developments make it practical to use the spread between body temperature and the ambient air. The energy harvesting devices are rigid, however, which poses problems for applications that use the human body as a heat source. The system needs to be flexible to conform with the changing shape of a human wrist or other body part. To get the most energy from body heat, the device needs to remain in close contact with the skin at all times.

Researchers at North Carolina State University have come up with a solution. They connect tiny, rigid thermoelectric components with liquid metal to create a flexible system. The non-toxic metal alloy uses gallium and indium, and it creates a conductive liquid with very low electrical resistance. If a connection should break due to the device being bent, the alloy can “heal” itself to reestablish the electrical connection.

This approach could be key to wearable devices that can generate their own power from body heat, eliminating the need to recharge them at frequent intervals.