North Carolina State University engineers have created a flexible thermoelectric energy harvester that uses body heat as its only source of energy to power wearable electronic devices.
“We wanted to design a flexible thermoelectric harvester that does not compromise on the material quality of rigid devices yet provides similar or better efficiency,” said NC State professor Mehmet Ozturk. “Using rigid devices is not the best option when you consider a number of different factors.”
The new harvester boasts of superior contact resistance – or skin contact – with flexible devices, as well as the ergonomic and comfort considerations to the device wearer.
Ozturk said that he and colleagues Michael Dickey and Daryoosh Vashaee 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.
Ozturk said one of the key challenges of a flexible harvester is to connect thermoelectric elements in series using reliable, low-resistivity interconnects.
“We use a liquid metal of gallium and indium – a common, non-toxic alloy called EGaIn – to connect the thermoelectric legs,” Ozturk said. “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: If a connection is broken, the liquid metal will reconnect to make the device work efficiently again. Rigid devices are not able to heal themselves,” Ozturk added.
Ozturk said future work will focus on improving the efficiencies of these flexible devices, by using materials and techniques to further eliminate parasitic resistances.
Image credits and content: Mehmet Ozturk/NC State University