Portable gadgets get boost from knees up

For those among us that are fond of the odd gadget, but don’t want to waste time charging them at home, then fear not scientists have created a new machine that harvests energy from the movement of the knees while walking.

New device could be used in remote regions

The apparatus captures the energy of a person's movement by coupling an electrical generator to knee motion. When the wearer extends the knee, a gear on the device turns and spins the generator, which builds up energy. When the knee is flexed, the device turns off so as not to tax the wearer. The machine senses motion and knows when to activate itself.

“Since muscles are the powerhouses of the body, my colleagues and I designed our device to generate electricity from the motion of the knee joint,” said Max Donelan, director of the Locomotion Laboratory at Simon Fraser University in Canada. “It resembles a knee brace and weighs about 1.5kg including the gearing and generator.”

Six volunteers wore the devices on their legs while strolling on a treadmill and were able to produce about five watts of electrical power each. That's enough energy to run 10 mobile phones simultaneously.

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

The device could be used to power computers in remote regions where electricity is scarce, Donelan said.

Results from tests of the device were published in the 8 February issue of the journal, Science.