Fitness trackers and wearable devices often face the issue of running out of battery. However, imagine a future where wearable technology could harness body heat to power itself.
Researchers at UW have created a flexible, durable electronic prototype that can capture energy from body heat and convert it into electricity, capable of powering small electronics like batteries, sensors, or LEDs. This device remains functional even after being pierced multiple times and stretched 2,000 times.
“I had this vision a long time ago,” said senior author Mohammad Malakooti, UW assistant professor of mechanical engineering. “When you put this device on your skin, it uses your body heat to directly power an LED. As soon as you put the device on, the LED lights up. This wasn’t possible before.”
Traditionally, devices that utilize heat to generate electricity are rigid and fragile. However, Malakooti and the team have developed a highly flexible and soft device that can conform to the contours of an individual’s arm.
This device was meticulously designed from the ground up. The researchers conducted simulations to identify the optimal combination of materials and device structures and subsequently manufactured nearly all the components in their laboratory.
It consists of three primary layers. The core comprises rigid thermoelectric semiconductors responsible for converting heat into electricity. These semiconductors are encased in 3D-printed composites with low thermal conductivity, which enhances energy conversion and reduces the device’s overall weight. To impart stretchability, conductivity, and electrical self-healing, the semiconductors are linked with printed liquid metal traces.
Furthermore, liquid metal droplets are integrated into the outer layers to enhance heat transfer to the semiconductors and maintain flexibility, as the metal remains in liquid form at room temperature. All components, with the exception of the semiconductors, were designed and produced in Malakooti’s laboratory.
In addition to wearables, Malakooti mentioned that these devices could have valuable applications in other fields. One potential use is to integrate these devices with heat-producing electronics.
“You can imagine sticking these onto warm electronics and using that excess heat to power small sensors,” Malakooti said. “This could be especially helpful in data centers, where servers and computing equipment consume substantial electricity and generate heat, requiring even more electricity to keep them cool. Our devices can capture that heat and repurpose it to power temperature and humidity sensors. This approach is more sustainable because it creates a standalone system that monitors conditions while reducing overall energy consumption. Plus, there’s no need to worry about maintenance, changing batteries, or adding new wiring.”
The potential applications of these devices also extend to reverse operations. This means that by introducing electricity, these devices can be utilized to heat or cool surfaces, opening up new possibilities for their use.
“We’re hoping someday to add this technology to virtual reality systems and other wearable accessories to create hot and cold sensations on the skin or enhance overall comfort,” Malakooti said. “But we’re not there yet. For now, we’re starting with efficient, durable wearables that provide temperature feedback.”
The other contributors to this research are Youngshang Han, a doctoral student in mechanical engineering at UW, and Halil Tetik, who conducted this research as a postdoctoral scholar at UW in mechanical engineering and is currently an assistant professor at Izmir Institute of Technology. Both Malakooti and Han are affiliated with the UW Institute for Nano-Engineered Systems. This research was supported by funding from the National Science Foundation, Meta, and The Boeing Company.
Journal reference:
- Youngshang Han, Halil Tetik, Mohammad H. Malakooti. 3D Soft Architectures for Stretchable Thermoelectric Wearables with Electrical Self-Healing and Damage Tolerance. Advanced Materials, 2024; DOI: 10.1002/adma.202407073