Kinetic Energy to Power Cell Phones

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“Human walking carries a lot of energy,” says professor of mechanical engineering at the University of Wisconsin-Madison, Tom Krupenkin. “Theoretical estimates show that it can produce up to 10 watts per shoe, and that energy is just wasted as heat. A total of 20 watts from walking is not a small thing, especially compared to the power requirements of the majority of modern mobile devices.” (Reported in Gizmag.com)

Through energy harvesting tiles, backpacks, and insoles, there has been much talk about harnessing kinetic energy to power mobile devices and other electronics. A team of researchers is claiming to have made a big breakthrough in the collective effort to turn human motion into usable energy, developing a new method of producing useful amounts of electricity from our footsteps.

The biggest obstacle has been how to harvest the kinetic energy produced by our footfalls. But the researchers at UW-Madison think they have found an answer: reverse electrowetting, a new technology involving a conductive liquid that interacts with a nanofilm-coated surface to produce electrical energy.

The difficulty with this technology is that it requires an energy source with a reasonably high frequency, higher than that produced by human motion.

Bubbles Are the Answer

To address this problem, the researchers combined reverse electrowetting with a novel device called a bubbler in an effort to bridge the gap. The bubbler contains no moving mechanical parts, but is made up of two flat plates with a conductive liquid in between. In the bottom plate, tiny holes allow pressurized gas to enter, which in turn forms bubbles. These grow in size until they make contact with the top plate and burst. The rapid, ongoing production and bursting of bubbles washes the conductive fluid back and forth to generate an electrical charge.

They claim that theoretical estimates indicate up to 10 kW might be possible. The shoes could be used to power mobile devices through a charging cable, be adapted for the military, or act as a power source for people in remote areas and developing countries.

Krupenkin and J. Ashley Taylor, a senior scientist in UW–Madison’s Mechanical Engineering Department, have created a startup company called InStep NanoPower, and are seeking industry partners to commercialize the technology. They have already teamed with Vibram in develop a demonstrator shoe with the energy-harvesting technology embedded in the sole.

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