Researchers at CU Boulder have developed a new, low-cost, wearable device that transforms the human body into a biological battery. The device is stretchy enough that you can wear it like a ring, a bracelet, or any other accessory that touches your skin. It taps into a person’s natural heat — employing thermoelectric generators to convert the body’s internal temperature into electricity.
The concept may sound like something out of The Matrix film series, in which a race of robots has enslaved humans to harvest their precious organic energy. Professor Jianliang Xiao and his colleagues aren’t that ambitious: Their devices can generate about 1 volt for every square centimeter of skin — less voltage per area than what most existing batteries provide but still enough to power electronics like watches or fitness trackers.
Scientists have previously experimented with similar thermoelectric wearable devices, but Xiao’s is stretchy, can heal itself when damaged, and is fully recyclable — making it a cleaner alternative. “Whenever you use a battery, you’re depleting that battery and will eventually need to replace it,” Xiao said. “The nice thing about our thermoelectric device is that you can wear it, and it provides you with constant power.”
The group’s latest innovation begins with a base made out of a stretchy material called polyimine. The scientists then stick a series of thin thermoelectric chips into that base, connecting them all with liquid metal wires. The final product looks like a cross between a plastic bracelet and a miniature computer motherboard or maybe a techy diamond ring. “Our design makes the whole system stretchable without introducing much strain to the thermoelectric material, which can be really brittle,” Xiao said.
Just pretend that you’re out for a jog. As you exercise, your body heats up, and that heat will radiate out to the cool air around you. Xiao’s device captures that flow of energy rather than letting it go to waste. “The thermoelectric generators are in close contact with the human body, and they can use the heat that would normally be dissipated into the environment,” he said. He added that you can easily boost that power by adding in more blocks of generators. “What I can do is combine these smaller units to get a bigger unit,” he said. “It’s like putting together a bunch of small Lego pieces to make a large structure. It gives you a lot of options for customization.”
Xiao and his colleagues calculated, for example, that a person taking a brisk walk could use a device the size of a typical sports wristband to generate about 5 volts of electricity — which is more than what many watch batteries can muster.
The new devices are as resilient as biological tissue. If your device tears, for example, you can pinch together the broken ends, and they’ll seal back up in just a few minutes. And when you’re done with the device, you can dunk it into a special solution that will separate out the electronic components and dissolve the polyimine base — each and every one of those ingredients can then be reused.
“We’re trying to make our devices as cheap and reliable as possible, while also having as close to zero impact on the environment as possible,” Xiao said. While there are still kinks to work out in the design, he thinks that his group’s devices could appear on the market in five to 10 years.