Researchers have enhanced a flexible body heat harvester by preventing heat leakage. The harvesters use heat energy from the human body to power wearable technologies. The technology relies on the same principles governing rigid thermoelectric harvesters that convert heat to electrical energy.
Flexible harvesters that conform to the human body are highly desired for use with wearable technologies. Flexible thermoelectric generators (TEGs) provide superior skin contact with flexible devices as well as ergonomic and comfort considerations to the device wearer. The performance and efficiency of flexible harvesters, however, historically trail well behind rigid devices, which have been superior in their ability to convert body heat into usable energy.
The TEG originally employed semiconductor elements that were connected electrically in series using liquidmetal interconnects made of EGaIn — a non-toxic alloy of gallium and indium. EGaIn provided both metal-like electrical conductivity and stretchability. The entire device was embedded in a stretchable silicone elastomer.
The upgraded device employed the same architecture but significantly improved the thermal engineering of the previous version, while increasing the density of the semiconductor elements responsible for converting heat into electricity. One of the improvements was a high-thermal-conductivity silicone elastomer — essentially a type of rubber — that encapsulated the EGaIn interconnects.
The newest iteration adds aerogel flakes to the silicone elastomer to reduce the elastomer’s thermal conductivity. Experimental results showed that this innovation reduced the heat leakage through the elastomer by half. The aerogel stops the heat from leaking between the device’s thermoelectric “legs.” The higher the heat leakage, the lower the temperature that develops across the device, which translates to lower output power.
The latest iteration of the flexible device performs an order of magnitude better than the original device. The technology employs the same semiconductor elements used in rigid devices perfected after decades of research. The approach also provides a low-cost opportunity to existing rigid thermoelectric module manufacturers to enter the flexible thermoelectric market.