Flexible device harvests thermal energy to power wearables

University of Washington researchers have developed an innovative solution to continuously powering wearable electronic devices, such as health and fitness trackers to virtual reality headsets. But finding ways to continuously power these devices is a challenge. Researchers have uncovered what they call the “first-of-its kind” flexible, wearable thermoelectric device that converts body heat to electricity. The device is soft and stretchable, yet sturdy and efficient — properties that can be challenging to combine.

“It’s a 100% gain if we harvest thermal energy that would otherwise be wasted to the surroundings. Because we want to use that energy for self-powered electronics, a higher power density is needed,” said Mohammad Malakooti, a UW assistant professor of mechanical engineering. “We leverage additive manufacturing to fabricate stretchable electronics, increase their efficiency and enable their seamless integration into wearables while answering fundamental research questions.”

Source: University of Washington

Even after more than 15,000 stretching cycles at 30% strain, the researchers’ prototype device remains fully functional, a highly desirable feature for wearable electronics and soft robotics. The device also shows a 6.5 times increase in power density compared to previous stretchable thermoelectric generators. For further information see the IDTechEx report on Thermoelectric Energy Harvesting and Other Zero-Emission Electricity from Heat 2022-2042.

Alloys address limitations

To create these flexible devices, the researchers 3D printed composites with engineered functional and structural properties at each layer. The filler material contained liquid metal alloys, which provide high electrical and thermal conductivity. These alloys address limitations in previous devices, including an inability to stretch, inefficient heat transfer and a complex fabrication process. The team also embedded hollow microspheres to direct the heat to the semiconductors at the core layer and reduce the weight of the device.

The researchers showed that they could print these devices on stretchable textile fabrics and curved surfaces, which suggests that future devices could be applied to clothing and other objects. The team is excited about the future possibilities and real-life applications of wearable electronics.

“One unique aspect of our research is that it covers the whole spectrum, all the way from material synthesis to device fabrication and characterization,” said Malakooti, who is also a researcher in the UW’s Institute for Nano-Engineered Systems. “This gives us the freedom to design new materials, engineer every step in the process and be creative.”