Harnessing 'people power'

Dr. Donelan behind a close-up of the knee brace.

Researchers have created a device that looks like a knee brace, which converts the energy from a walking person’s moving leg into electricity.

A new, knee-mounted device harvests energy from the end of a walker's step, in the same way that hybrid-electric cars recycle power from braking.

With one of the devices on each leg, volunteers generated about 5 Watts of electricity, without breaking a sweat. That’s enough power to run 10 cell phones at the same time, and twice the power needed for computers in developing regions of the world.

Maxwell Donelan of Simon Fraser University in British Columbia and his colleagues rigged the knee brace with a generator system that takes the physical motion of the knee (mechanical energy) and turns it into electricity (electrical energy).

Our hamstring muscles slow our knees when we walk, absorbing the energy of each step. The knee-brace device helps the muscles do this and then “harvests” the extra energy, to convert it into electricity. And, the person wearing the devices barely notices the difference.

The researchers monitored six volunteers wore the devices while walking slowly on treadmills. They measured each person’s oxygen use and carbon-dioxide production to learn how much energy it takes to work the devices

They found that the devices allowed walkers to produce about 5 Watts of electrical power, while exerting little additional energy.

Dr. Donelan noted that a half- billion children live without electricity and perhaps this “people power” strategy might prove useful in remote regions for powering computers. There are many other possible uses for this device, including driving robotic arms, for people with missing limbs or hands, or charging electrical equipment that soldiers carry into the field.

The findings appear in the 8 February 2008 issue of the journal Science.

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