Charging batteries--a walk in the park.

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Simon Fraser University (SFU) researchers have developed a new wearable technology that generates electricity from the natural motion of walking. It promises to revolutionize the way we charge portable battery-powered devices.

The biomechanical energy harvester, featured in a recent issue of the journal Science, resembles a lightweight orthopedic knee brace. The device harvests energy from the end of a walker's step, when the muscles are working to slow the movement of the leg, in much the same way that hybrid-electric cars recycle power from braking.

Wearing a device on each leg, an individual can generate up to five watts of electricity with little additional physical effort. Walking more quickly generates as much as 13 watts of electricity. At that rate, one minute of walking provides enough electricity to sustain 30 minutes of talk time on a mobile phone.

"This technology promises to have significant medical, military, and consumer applications," said lead author Max Donelan, an assistant professor of kinesiology and associate member of engineering science at SFU. "A fully charged battery pack represents more than just a mere convenience. It allows a soldier to get back home safely. It benefits stroke victims, amputees, and others who rely on power-assisted medical devices for mobility. It means a better quality of life for the developing world, where a half-billion children live without easy access to electricity. And of course, it is a necessity to anyone in the developed world who has come to rely on portable electronics for work or play."

The biomechanical energy harvester is rigged with a generator, clutch, gears, and a real-time control system to selectively engage and disengage power generation. It works in much the same way that regenerative brakes charge batteries in hybrid vehicles. Regenerative brakes collect the kinetic energy that would otherwise be dissipated as heat when the car slows down. Similarly, the harvester collects the energy typically lost when the muscles of the body slow the knee after swinging the leg forward to take a step.

Donelan's research team is supported by funding from the Michael Smith Foundation for Health Research, the Natural Sciences and Engineering Research Council of Canada, and the Canadian Institutes for Health Research. Donelan plans to have a working prototype available within 18 months through his spinoff company, Bionic Power Inc.

Simon Fraser University