One of the drawbacks of fitness trackers and other wearable devices is that their batteries eventually run out of juice. But what if, in the future, wearable technology could use body heat to power itself?
University of Washington (UW) researchers have developed a flexible, durable electronic prototype that can harvest energy from body heat and turn it into electricity that can be used to power small electronics, such as batteries, sensors, or LEDs. This device is also resilient — it still functions even after being pierced several times and then stretched 2,000 times.
The team detailed these prototypes in a paper published in Advanced Materials.
“I had this vision a long time ago,” said Senior Author Mohammad Malakooti, Ph.D., 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 use heat to generate electricity are rigid and brittle, but Malakooti and team previously created one that is highly flexible and soft so that it can conform to the shape of someone’s arm.
This device was designed from scratch. The researchers started with simulations to determine the best combination of materials and device structures and then created almost all the components in the lab.
It has three main layers. At the center are rigid thermoelectric semiconductors that do the work of converting heat to electricity. These semiconductors are surrounded by 3D-printed composites with low thermal conductivity, which enhances energy conversion and reduces the device’s weight. To provide stretchability, conductivity, and electrical self-healing, the semiconductors are connected with printed liquid metal traces. Additionally, liquid metal droplets are embedded in the outer layers to improve heat transfer to the semiconductors and maintain flexibility because the metal remains liquid at room temperature. Everything except the semiconductors was designed and developed in Malakooti’s lab.
In addition to wearables, these devices could be useful in other applications, Malakooti said. One idea involves using these devices with electronics that get hot.
“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.”
These devices also work in reverse, in that adding electricity allows them to heat or cool surfaces, which opens up another avenue for applications.
“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 wearables that are efficient, durable and provide temperature feedback.”
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Malakooti.
Tech Briefs: What was the biggest technical challenge you faced while developing this wearable prototype?
Malakooti: The biggest technical challenge was enhancing the energy harvesting performance at low temperature gradients while making sure that the wearable prototype remained highly flexible and durable for practical applications.
Tech Briefs: How did this project come about? What was the catalyst for your work?
Malakooti: The idea of energy harvesting has always fascinated me. About five years ago, while we were developing composite materials that offered both high thermal conductivity and flexibility, I began exploring wearable thermoelectric generators and identified key technological bottlenecks. Our main advantage was the ability to use advanced materials and tailor their mechanical, electrical, and thermal properties, which ultimately led us to design and fabricate these high-performance thermoelectric wearables.
Tech Briefs: Can you explain in simple terms how it works?
Malakooti: This wearable device contains thermoelectric semiconductors that can convert heat into electricity and vice versa. When placed on the body, it harnesses the warmth of your skin to generate electricity. We designed the device to be highly flexible, allowing it to conform to curved surfaces, like the human body, which enhances its performance and increases output power.
Tech Briefs: Do you have plans for further research/work/etc. to achieve the VR and other wearable additions?
Malakooti: Yes, as I mentioned, we are actively developing new prototypes. Our plan involves creating flexible circuits that will be integrated into our devices for effective temperature control. Additionally, we are designing thermo-haptic wearables that will offer comfort and rapid response.
Tech Briefs: If not, what are your next steps, where do you go from here?
Malakooti: Our next steps include conducting thorough testing to evaluate their performance. We will gather feedback to refine our designs further. We also plan to explore collaborations with industry partners to enhance the integration of our technology into existing VR systems and other wearable accessories.
Tech Briefs: I know the article was published very recently, but do you have any updates you can share?
Malakooti: At this time, we don’t have any specific updates to share beyond the fact that we are taking initial steps toward commercialization and exploring various practical use cases for our technology.
Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition, broadly speaking?
Malakooti: My advice is to be persistent and curious. Don’t get discouraged when results don’t match your expectations; instead, strive to understand the reasons behind any setbacks. This mindset will keep you moving forward and ultimately help you bring your ideas to reality.
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