Flexible Film Captures Energy from Human Motion

A paper-thin, flexible material increases its voltage every time it is folded. (Image credit: Michigan State University)

At least once a week, Nelson Sepulveda gets on one of his bikes and rides 35 miles or more. He gets a good workout on those days, but as an associate professor of electrical and computer engineering at Michigan State University, he knows some of it is wasted energy. All of that pedaling could be harnessed and converted into electricity to power his phone or some other electronic gadget.

This week, Sepulveda and his colleagues report in the journal Nano Energy on a new film-like material capable of turning motion into electricity. The material is similar to other piezoelectrics in that it generates a voltage when it's squeezed or pressed. But what sets this one apart is that it's paper thin and flexible and each time it's folded, the voltage increases.

"This increased voltage upon folding is not possible using other solid piezoelectric materials," Sepulveda told Seeker.

If that voltage could be efficiently directed into a current, it could reduce the nuisance of recharging or even eliminate it.

'What if you could take the mechanical energy from swiping pages on your tablet and use that to charge the battery of the device itself?" said Sepulveda. "That could reduce the time required to recharge your device."

To create the device, Sepulveda and his team used a combination of fabrication techniques and thin layers of substances including silver, polyimide, polypropylene ferroelectret and electrically charged particles onto a silicon wafer, creating a sheet that was peeled away from the chip as if it were a sticker.

The researchers conducted a few tests using different sizes of the piezoelectic sheet to measure its voltage. In one test a palm-sized sheet cranked out about 50 volts was able to power 20 LED lights.

When they folded the film-like piezoelectric material, the voltage increased exponentially.

Although producing a high voltage is promising, said Sepulveda, it's not enough. The researchers need to tweak the material so that its energy potential can be converted into a current. Sepulveda compared the voltage to water contained in a huge tower at the top of a mountain. The water pressure would be enormous.

"But that's just the force," he said.

The water's flow — it's current — depends on the pipes. How big are they? How long are they? What route do they take? If there are no pipes or the pipes take a convoluted route, the pressure may be very small by the time the water reaches a home faucet.

It's the same for voltage. "I could have a million volts and no current," he said.

Sepulveda told Seeker that he and his team have engineered at least one solution to converting the high voltage generated by the device into a flow of charge, but they were still trying to nail down the science of why it worked. He said it was too early to discuss the details.

One day soon, though, he could have a wearable device that attaches to his knee and generates power while he bikes. That would turn his 35-mile ride into an energy-harvesting bonanza.

'That should probably give me enough energy to charge my cellphone," he said.

Original article on Seeker.

Tracy Staedter is a science journalist with more than 20 years of experience. She has worked as an editor for Seeker, Discovery, MIT Technology Review, Scientific American Explorations, Astronomy and Earth and authored the children’s science book, Rocks and Minerals, part of the Reader’s Digest Pathfinders series. In 2013, she founded the Boston-based writing workshop Fresh Pond Writers.