Warming Up to Energy Harvesting

Researchers made a flexible thermoelectric system to harvest energy from body heat, offering a durable, battery-free solution for wearables.

Nick Bild
4 months agoWearables
Powering an LED with body heat (📷: University of Washington)

No matter how small electronic components get, wearable devices will still be limited by power delivery systems. Today, power is almost invariably supplied to these devices by batteries. And where there are batteries, there are rigid, bulky, and uncomfortable bricks that we need to carry around with us. Furthermore, batteries have a limited capacity, which means regular recharges and all of the inconveniences that come with them. Not only does the user have to remember to charge their device on a regular schedule, but it is also unavailable for use during that time.

The small size of wearable devices generally rules out sources of power like solar and other renewables. In addition to lacking adequate surface area for these technologies, these sources are often unavailable as the wearer goes about their normal daily activities. But a promising technology developed by a trio of researchers at the University of Washington may soon overcome these issues and give us a more practical and convenient way to power the next generation of wearables. They have developed a soft and flexible system that can harvest energy from the wearer’s body heat.

Harvesting energy from temperature differences is by no means a new idea, however existing technologies are rigid and brittle, which makes them impractical for use in wearable devices. But by taking a new approach, the team has made a thermoelectric energy harvester that can comfortably conform to the shape of the body. Moreover, testing shows that the device is very durable — even after being stretched and bent thousands of times, its performance is not degraded.

To bring this energy harvester to life, the researchers came up with a three-layer design. In the middle of the stack of layers is an array of traditional thermoelectric semiconductors that convert heat into electrical energy. This layer is sandwiched between 3D-printed composite materials with low thermal conductivity. These materials are light in weight and also serve to enhance the rate of energy conversion.

Flexibility was made possible by incorporating liquid metal traces into the design to form the circuit. These conductive traces can move with the wearer as they bend and flex without breaking the circuit. Droplets of liquid metal were also added to the outer layers to enhance heat transfer between them and the inner layer containing the semiconductors.

In addition to use in wearables, this technology could also be put to work in other applications where heat is consistently generated, like in data centers. The team suggested that it could be used to power sensors that monitor environmental parameters without increasing energy consumption.

Another interesting aspect of this system is that it can be used in reverse. By adding power, the patches can be used to heat or cool the surface they are attached to. These properties may open the door to even more potential applications in the future.

Nick Bild
R&D, creativity, and building the next big thing you never knew you wanted are my specialties.
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