Remember the last time the battery on your cellphone died in the middle of a conversation?

Tom Krupenkin, a UW-Madison physicist and researcher, sympathizes. Actually, he’s done more than that. He and another university scientist may have come up with a way to dramatically extend the life of a cellphone battery.

And here’s the really nifty part: Their invention will allow you to keep your phone charged simply by walking.

Krupenkin and J. Ashley Taylor have invented a device that fits in the bottom of a shoe and converts the mechanical motion of walking into electrical energy. Though it is still years from commercial use, the researchers have a working prototype. They’re scientists so, of course, they had to give their invention a fancy name — the “footwear-embedded harvester.”

Here’s how it works. Two small pouches are filled with a fluid that is designed using nanotechnology to generate an electrical current when compressed over and over again by the up and down motion of the foot. The researchers also came up with a name for this unique process: “reverse electrowetting.”

While it would be possible to connect a cellphone directly to the harvester, Krupenkin said the researchers came up with a less cumbersome approach. During their research, they found that most of the battery power in a cellphone gets used up searching for and connecting to hot spots or the signals from cellphone towers. So the scientists incorporated a Wi-Fi hot spot transmitter into the harvester. The harvester, instead of the battery in the phone, powers the hot spot device.

“You cut the power requirements of your cellphone dramatically by doing this,” Krupenkin said. “Your cellphone battery will last 10 times longer.”

But Krupenkin also said it will be possible to connect a phone directly to the harvester. Such a connection would be especially useful for soldiers or law enforcement officers who are in the field.

The device also has great potential for use in developing countries, Krupenkin said, where electricity for charging batteries is often not available. In such places, losing battery power and communication can sometimes be life threatening, Krupenkin said.

And the device has the potential for powering other portable electronic gadgets such as laptops and flashlights. Because it produces energy in the single watt range, it fills a void between high-power producers such as windmills and solar panels and the very low-power batteries that run watches and calculators.

Krupenkin and Taylor have taken the first steps toward commercializing their invention. They’ve started a company called InStep Nanopower. And they’re looking for shoe manufacturers who can help them design a shoe.

Little did Krupenkin know that his lifelong pursuit of physics would lead to shoe shopping.

“It’s been a very complex blend of engineering, science and art,” he said.

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