Z. L. Wang and X. D. Wang/Georgia Institute of Technology

Microdynamo. Nanoscale zinc oxide bristles convert mechanical energy into electric current.

So Long, Energizer Bunny

Researchers have developed an extremely tiny generator that can produce electricity from the mechanical energy naturally produced when our bodies move. With further development, the nanogenerator could allow people to power personal electronic devices, such as cell phones, MP3 players, and maybe even small laptop computers, entirely from the physical exertions of a day at the office. It could also usher in a new era of long-lived microsensors and miniature medical devices that derive their electrical needs from their surroundings instead of from batteries.

First demonstrated in the 1880s, the ability of some materials to convert mechanical pressure into an electric current--called the piezoelectric effect--has found scattered applications over the years. For example, it powers the flashing LEDs embedded in the soles of children's sneakers, and it produces sparks to ignite propane-fueled candle and fireplace lighters. But so far, no one has been able to channel this essentially free power into very small applications--particularly at the nanoscale, where devices can be thousands of times smaller than the thickness of a human hair. Nanosized piezoelectric devices would be extremely valuable because they could operate indefinitely without the need to be repowered or recharged.

Now, a researcher at the Georgia Institute of Technology in Atlanta may have achieved a breakthrough. At a presentation today at the American Chemical Society's National Meeting in Salt Lake City, Utah, materials scientist Z. L. Wang described the first nanogenerator. The device relies on flexible zinc oxide nanowires sprouting like bristles from a metal electrode and sandwiched inside a rigid polymer binding. When pressed, the polymer bends the zinc oxide filaments, which generate an electrical current.

So far, Wang's team has been able to generate 0.2 volts with an efficiency of only 6.8%--far below the performance of conventional batteries. Still, he says, that's already enough for some practical applications, if many nanogenerators are integrated.

The nanogenerator could be a groundbreaking innovation in powering standalone devices, says Daniel Eils, a graduate student in mechanical engineering at the University of Texas, Austin. Eils, who is working on similar research, says the concept "could mature rapidly, as the nanogenerator design begins to incorporate existing advances in nanotechnology and integrated circuitry."

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