Northwest scientists create a flexible ‘fabric’ that converts body heat into electricity

Mohammad Malakooti has a look in his eye — like a man who wants to break something.

“We are going to actually go to 700% to make sure it’s going to break,” he said. “You know, sometimes we need to push the boundaries.”

It’s late winter on the University of Washington campus, and the “something” Malakooti wants to pull to seven-times its original size looks like a thick gray Band-Aid. It’s squishy to the touch, but with metal semiconductors inside that allow the stretchable device to convert heat into electricity.

“It can basically generate electrical energy from your body heat. You don’t have to do [anything],” Ph.D. candidate Youngshang Han said. “As long as I’m alive, I can harvest energy.”

At first, Han seems a bit bewildered that his boss wants to fully break one of their prototypes. But they’ve already flexed it, stretched it and punctured it repeatedly with a pin – and it still works. So he’s all in.

The test starts, and the material begins to narrow and thins under the strain. The semiconductors inside bulge at the surface like bones under skin.

A beep rings out, signaling the device has lost the ability to conduct electricity, but structurally, the band doesn’t rip apart.

“It survived. It’s just too strong,” Han said, laughing.

Their new power-generating band is technically called a thermoelectric device, and the engineers hope it can become an alternate source of electricity to help power our increasingly electronics-reliant world.

Turning heat into electricity

Heat is a form of energy, yet much of the heat we produce in our world — in factories, vehicles and even with our bodies — just vanishes into the air.

“Our body generates heat and dissipates it to the environment,” Malakooti said. “And this idea for wearable thermoelectric devices is: let’s recover that heat and use it for powering the small electronics or wearable sensors.”

It could run low-power sensors that could monitor your temperature and heart rate. It could also be used in factories to make electricity from waste heat coming from hot pipes and machinery.

The basic technology relies on a physics phenomena called the Seebeck effect. When one side is placed on something hot — like your skin — and the other side is colder, it generates electricity. The more you increase the difference in temperature between the two sides, the more electricity it makes.

“If you put the entire device in an oven, you won’t generate any electricity because there is no temperature gradient,” he says.

This heat-to-electricity phenomenon the researchers are harnessing isn’t new. NASA has used thermoelectric generators to power its probes and Mars rovers for decades, using red-hot radioactive plutonium as a heat source and the cold of deep space to keep the temperature difference high. That temperature gap can be more than 1,500 degrees Fahrenheit.

But generating usable amounts of power with your body heat at room temperature is a much different challenge. The team has achieved this by developing new materials that can be 3D-printed into stretchable, flexible layers that encase the bone-like semiconductors.

These layers keep the cold side cold and the hot side hot to maximize the production of electricity. It also creates a flexible, stretchable substrate that can bend to maintain contact with skin as it moves — essentially creating wearable power generators.

To show how it works, they have integrated one of Band-Aid-sized devices into a cuff that straps onto your forearm. As soon as the device hits the skin, a tiny red LED illuminates.

“It might not be that impressive for the people outside this field, but powering an LED with your body at room temperature, this is another level. A huge jump from the status quo,” Han said.

Other possibilities

In recent years, the development of wearable electronics has exploded.

“I think it relates to the Internet of Things,” said Chih-hung Chang, Stephen Slavens Faculty Scholar at Oregon State University. Chang is not involved in the University of Washington research.

The Internet of Things is the idea of having a network of physical objects connected, monitored, and potentially controlled through computer systems and the Internet. Humans are increasingly part of these interconnected systems, which means you need devices people don’t mind carrying around.

“People see the possibility of having wearable electronics compared to the more rigid form of electronics,” he said. “There’s certainly a lot of interest in moving in that direction.”

And the idea of self-powered wearable electronics — like the devices being made by the University of Washington team — is attractive.

“Just think about your phone,” Chang said. “If you don’t have to charge it all the time and look for the plug-in to have power, that would enable a lot of freedom. You can see the value of that: If you want to have [24/7 continuous] data of your glucose levels, this would be a way to enable that.”

Generating power is just one function of the thermoelectric devices being developed by Malakooti and Han, but they have other ideas for how their new wearable technology can be used.

When the team’s LED cuff generates electricity from body heat, the spot where the soft device rests on skin starts to feel surprisingly cold — like a piece of metal.

“That part of your skin is losing temperature. So it should feel cold because now the device is using that heat to power the LED,” Malakooti explained.

Their flexible design opens the door for wearable cooling systems.

“Imagine you’re working out, you’re getting hot. You can have this for thermoregulation,” he said.

While the possibilities are numerous, these devices are not going to be powering our cities anytime soon.

“We need to be realistic. We are talking about milliwatts, we are not talking about watts or megawatts,” Malakooti said. “So this is not going to address the energy crisis in the world. It’s more like self-sustainable electronics.”

Think health monitors, weather gauges, smart kitchens — maybe even converting heat waste from electric vehicle batteries back into usable electricity.

And in a world that seems to need more and more energy every day, tapping into waste heat to help power our lives is a tantalizing solution.

“I kind of feel like I’m a dreamer. I dream about the possibilities,” Malakooti said. “I feel like we are discovering new phenomena. We are showing new applications. Possibilities that [are going to], maybe at some point, change our lives.”