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Shoes redefine 'power walking'

Researchers are developing prototype shoes that harvest energy as their wearers walk around. The energy captured is enough to power portable gadgets such as cell phones.
Researchers are developing prototype shoes that harvest energy as their wearers walk around. The energy captured is enough to power portable gadgets such as cell phones.Instep Nanopower

Going on a power walk could soon do more than blow off steam; it could recharge your cell phone and other portable electronics, according to engineers working on a new way to harvest the mechanical energy in the human gait.

The concept is called reverse electrowetting. It uses a micro-fluidic device consisting of thousands of micro-droplets that move past a novel nanotechnology-based thin film. This motion of the droplets is converted into an electrical current.

"The normal way of using the harvester would be couple it with a tiny, rechargeable battery not unlike the ones which we have in cell phones," Tom Krupenkin, an engineering researcher at the University of Wisconsin-Madison, explained to me on Tuesday.

"That thing would accumulate the energy you generate while walking and would provide you this energy whenever you need it."

He and colleague Ashley Taylor reveal the details of how this works this week in the journal Nature Communications and are now at work commercializing the technology with electricity harvesting shoes though their company Instep Nanopower.

Power walkers

The market for the technology, according to Krupenkin, is huge. Potential customers range from military personnel who now carry 20 pounds of batteries in the field to keep their gadgets running to people in developing countries who have inadequate access to electrical grids for recharging their cell phones.

These users would likely just plug their devices into a tiny USB port in their shoes, happy enough to have a charge that they are not too bothered by wires snaking around their bodies. In countries like the U.S., though, wires coming out of footwear could be a fashion faux pas that's a step too far.

"I wouldn't like that idea myself," Krupenkin noted.

To get around the problem, he and Taylor envision equipping their footwear with tiny mobile hotspots that are powered by the electricity-generating shoes. The hotspot doesn’t charge your phone, but rather allows you to keep your phone in a low power state using technology such as Bluetooth.

The lion's share of cell phone battery drain, Krupenkin noted, is due to transmitting and receiving data over long range RF communications. The mobile hotspot does this task, allowing the phone to use the power sipping technology.

Relieved of having to communicate over long distances, "the battery of that device would last much, much longer," Krupenkin said. "Like a cell phone battery that lasts literally for a month instead of a day or two."

Technology improvement?

The idea of harvesting energy from moving bodies isn't new, though most attempts such as vibrating plates or piezoelectric materials only produce a few milliwatts of power. A person wearing the electricity harvesting shoes, the researchers say, could generate up to 20 watts of electrical power.

Other ideas such as a backpack that generates electricity as it bounces up on down while a person walks along produces several watts, but "you have to carry a very heavy backpack," Krupenkin said.

"Our technology is you have to carry your own weight anyway and your own weight is very substantial … but unlike the backpack, it is not extra weight, it is the weight that you have."

In concept, he noted, the shoes would not be noticeably different from what people wear around today. Of course, he added, taking a concept from the lab to the street is a bigger challenge than just inventing a new technology and proving that it works.

"Footwear is a very complex blend of art, engineering, biology, and things like that," Krupenkin said. "Creating good footwear is tricky and requires special knowledge and experience,"

The researchers are hoping to pair their power harvesting technology with a footwear company that has this expertise. That means people itching to get their hands on these shoes will have to wait at least a couple of years.

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John Roach is a contributing writer for