This knee brace could charge batteries

Scientists have developed a knee brace that captures energy from a moving knee, much like regenerative braking charges a battery in a Toyota Prius.

The device, jointly (hah!)developed by scientists at three universities, uses kinetic energy to generate electricity.

When the leg extends, energy spins gears on the device, which in turn power a built-in generator. Software determines at which point in each stride the generator should engage, and resistance from the engaged generator aids the wearer in slowing down the leg. See video of the knee in action.

Data on metabolic power supplied by the University of Michigan highlight the device's efficiency:


Brace yourself for the latest in battery-charging technology for gadgets. Researchers from Simon Fraser University in British Columbia have developed a device worn much like a knee brace that generates electricity from the natural motion of walking.

Here, Max Donelan, assistant professor of kinesiology, watches a demonstration of the Biomechanical Energy Harvester he developed with a team of researchers. 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," according to a release from the university.

Wearing a device on each leg, an individual can generate up to 5 watts of electricity with little additional physical effort, according to the release. Walking quickly, however, generates as much as 13 watts. At that rate, when the energy is stored in a battery, one minute of walking time could provide enough electricity to sustain 30 minutes of talk-time on a mobile phone.

"People are an excellent source of portable power--an average-sized person stores as much energy in fat as a 1,000 kg battery," Donelan said. "People recharge their 'body batteries' with food and, lucky for us, there is about as much useful energy in a 35-gram granola bar as in a 3.5 kg lithium-ion battery."