The device that produces electricity while walking. (Greg Ehlers/Simon Fraser University)

New Delhi, Feb. 7: A brisk walk might soon help bring a dead battery in a cellphone back to life. Researchers have developed a new device that will allow a person to generate electricity while walking.

A team of engineers from three universities in Canada and the US has developed a biomedical energy harvester worn on the knees that turns the mechanical energy of human muscles into electricity.

In experiments, volunteers who walked with one prototype device on each knee generated about 5 watts of electricity — sufficient to power 10 typical cellphones simultaneously.

“We’ve demonstrated proof of concept,” said Art Kuo, an associate professor of mechanical engineering at the University of Michigan. A description of the device developed by Kuo and his colleagues from the University of Pittsburgh and the Simon Fraser University in Canada will appear in the journal Science tomorrow.

The 1.6kg device harvests energy lost when a person brakes the knee after swinging the leg forward to take a step. A person has to spend less than one watt of extra power for each watt of electricity generated.

Kuo said the knee could be the best place in the human body to harvest energy. “We believe that when you’re slowing down the knee at the end of swinging the leg, most of that energy is just wasted,” Kuo said.

“The prototype device is heavy and bulky. But the energy generation part has very little effect on the wearer, whether it is turned on or not. We hope to improve it so that it is easier to carry,” Kuo said.

Hand-crank generators and wind-up flashlights or radios are among traditional devices that convert human body energy. But in the new knee-mounted harvester, the additional human body power required to produce one watt of electricity is less than one-eighth of that spent for conventional human power generation.

The new energy harvester could help extend the battery-life of insulin pumps, lighten equipment for mountain trekkers, or even help power prosthetic limbs in handicapped people.

In laboratory tests, the engineers tested the device on six men asked to walk on a treadmill at a leisurely pace of about 1.5 metres a second and measured their respiration to determine how hard they were working. The studies showed that substantial electricity could be generated with minimal increase in effort by the volunters.

The harvester is designed as a kneebrace with a small motor that serves as the generator and associated equipment. However, the researchers said future versions of the device would need to be constructed out of light-weight materials such as carbon fibre.

The knee muscles work cyclically with each step, accelerating while moving forward and decelerating while the leg comes to a halt with each step. The scientists said they focused on the knee because it has the highest level of available energy while walking.