Flexible Wearable Electronics use Body Heat as an Energy Source

In a recent proof-of-concept study, engineers from North Carolina State University have come up with a flexible thermoelectric energy harvester. The harvester is claimed to have the potential to power flexible wearable electronic devices using body heat as the only source of energy.

Wearable devices today are being used to monitor a variety of health and environmental measures. At the moment the performance and efficiency of flexible devices can not compare to rigid devices, which have been superior in their ability to convert body heat into usable energy.

According to the engineers, they wanted to design a flexible thermoelectric harvester that would not compromise on the material quality of rigid devices yet provide similar or better efficiency. Using rigid devices is not the best option when considering a number of different factors like superior contact resistance or skin contact as well as the ergonomic and comfort considerations of the device wearer. The engineers wanted to utilize the best thermoelectric materials used in rigid devices in a flexible package, so that manufacturers wouldn't need to develop new materials when creating flexible devices.

One of the key challenges of a flexible harvester is to connect thermoelectric elements in series using reliable, low-resistivity interconnects. The engineers used a liquid metal of gallium and indium - a common, non-toxic alloy called EGaIn - to connect the thermoelectric 'legs. The electric resistance of these connections is very low, which is critical since the generated power is inversely proportional to the resistance: Low resistance means more power. Using liquid metal also adds a self-healing function, meaning, if a connection is broken, the liquid metal will reconnect to make the device work efficiently again, unlike rigid devices.

The future work for now is said to be focused on improving the efficiencies of these flexible devices, by using materials and techniques to further eliminate parasitic resistances.

The work was described through a research paper by Mehmet Ozturk, Michael Dickey, Daryoosh Vashaee, Francisco Suarez, Dishit P. Parekh and Collin Ladd. The group also has a pending patent application on the technology.