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Take a hike with energy-harvesting rubber films

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Yi Qi, a postdoctoral researcher at Princeton University, holds a piece of silicone rubber imprinted with super-thin material that generates electricity when flexed. The technology could provide a source of power for mobile and medical devices. “As we get better at making these chips,” says Qi, “we’ll be able to make larger and larger sheets of them that will harvest more energy.”(Credit: Frank Wojciechowski)

PRINCETON (US)—Power-generating rubber films could make it possible to harness natural body movements—such as breathing and walking—to power pacemakers, mobile phones, and other electronic devices.

The material, composed of ceramic nanoribbons embedded onto silicone rubber sheets, generates electricity when flexed and is highly efficient at converting mechanical energy to electrical energy.

Shoes made of the material developed by Princeton University engineers may one day harvest the pounding of walking and running to power mobile electrical devices. Placed against the lungs, sheets of the material could use breathing motions to power pacemakers, obviating the current need for surgical replacement of the batteries that power the devices.

A paper describing the new material was published online in the journal Nano Letters.

The Princeton team is the first to successfully combine silicone and nanoribbons of lead zirconate titanate (PZT), a ceramic material that is piezoelectric, meaning it generates an electrical voltage when pressure is applied to it. Of all piezoelectric materials, PZT is the most efficient, able to convert 80 percent of the mechanical energy applied to it into electrical energy.

“PZT is 100 times more efficient than quartz, another piezoelectric material,” says Michael McAlpine, an assistant professor of mechanical and aerospace engineering at Princeton, who led the project. “You don’t generate that much power from walking or breathing, so you want to harness it as efficiently as possible.”

Fabrication starts with the researchers producing PZT nanoribbons—strips so narrow that 100 fit side-by-side in a space of a millimeter.

In a separate process, they embedded these ribbons into clear sheets of silicone rubber, creating what they call “piezo-rubber chips.” Silicone, which is used for cosmetic implants and medical devices, already is biocompatible. “The new electricity-harvesting devices could be implanted in the body to perpetually power medical devices, and the body wouldn’t reject them,” McAlpine says.

In addition to generating electricity when it is flexed, the opposite is true: The material flexes when electrical current is applied to it. This opens the door to other kinds of applications, such as use for microsurgical devices, he adds.

“The beauty of this is that it’s scalable,” says Yi Qi, a postdoctoral researcher who works with McAlpine. “As we get better at making these chips, we’ll be able to make larger and larger sheets of them that will harvest more energy.”

Qi and McAlpine collaborated with researchers and students from Princeton, the California Institute of Technology, and Morehouse College.

The research was funded by the U.S. Intelligence Community, a cooperative of federal intelligence and national security agencies.

Princeton University news: www.princeton.edu/main/news/

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