Power walking

 

Engineers have created a device that can capture energy from the simple act of walking.

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The team, which are from University of Michigan, Simon Fraser University in Canada and the University of Pittsburgh, have shown how the device can create enough power to operate a portable GPS locator, a mobile phone, a motorised prosthetic joint or an implanted neurotransmitter.

Resembling a regenerative braking system, the wearable device collects kinetic energy from the motion of walking, specifically from the action a knee makes in ‘braking’ after swinging the leg forward.

"There is power to be harvested from various places in the body, and you can use that to generate electricity. The knee is probably the best place. During walking, you dissipate energy in various places, when your foot hits the ground, for example. You have to make up for this by performing work with your muscles,” commented Arthur Kuo, an associate professor of mechanical engineering at the University of Michigan and an author of the paper.

Clever body

"The body is clever. In a lot of places where it could be dissipating energy, it may actually be storing it and getting it back elastically. Your tendons act like springs. In many places, we're not sure whether the energy is really being dissipated or you're just storing it temporarily. We believe that when you're slowing down the knee at the end of swinging the leg, most of that energy normally is just wasted," he continued.

In tests, subjects were examined walking at 2.2 miles per hour on a treadmill. For every watt of electricity generated the test group had to expend less than one watt of extra metabolic power. This compares very favourably – for example - with a hand-crank generator which needs approximately 6.4 watts of metabolic power to generate one watt of electricity.

"We've demonstrated proof of concept. The prototype device is bulky and heavy, and it does affect the wearer just to carry. But the energy generation part itself has very little effect on the wearer, whether it is turned on or not. We hope to improve the device so that it is easier to carry and to retain the energy-harvesting capabilities," concluded Kuo.
 

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