Knee Device Charges Portable Batteries

Researchers at Simon Frasier University in British Columbia have developed technology that generates electricity from the natural motion of walking. In an article published in the journal Science this month, Max Donelan, an assistant professor of kinesiology, and other team members say their biomechanical energy harvester promises to revolutionize the way people charge the batteries that power all sorts of mobile gear.

Their harvester, which straps across a knee joint just like an athletic knee brace, can generate up to five watts of electricity with little physical effort. And one minute of brisk walking can generate 13 watts -- enough to support 30 minutes of cell-phone use.

In much the same way that hybrid-electric cars recycle the power from braking, the wearable device harvests energy from the end of a walker's step, when the muscles are working to slow the movement of the leg, Donelan said.

"Humans are efficient converters of chemical energy," Donelan added. "There's a hundred times more energy in a granola bar than in an equivalent-sized battery."

A New Company

The technology has already been spun off to a new company called Bionic Power, which intends to make the energy harvester for military, medical and consumer applications. Though the prototype device weighs about 1.6 kg (3.5 pounds), Donelan believes commercial production units will end up weighing less than 1 kg (2.2 pounds).

"I think the early adopters will be people who are away from the electric grid -- like the hikers and emergency rescue workers who don't know when they will be able to recharge their batteries," said Donelan in a telephone interview. "Right now they end up carrying around large amounts of batteries, but they won't need to if they can treat themselves as the juice."

Bionic Power is taking a double-barreled approach by initially tackling military and medical applications. For example, soldiers in the field heavily rely on batteries for communications and navigation, and they typically need to carry up to 13 kg (28.6 pounds) of batteries to complete a 24-hour mission, Donelan said.

"Within the next 18 months we expect to have prototypes available for field testing to get feedback concerning how the technology can be integrated" into their gear, he said.

Reducing Costs

People who use the latest prosthetic limbs are also dependent on power. With the new technology, they will be able to "power off the healthy leg, and walk longer and faster," Donelan said. "If they generate power from their own motion, then batteries become less of a limitation, allowing the development of even more sophisticated gear."

Initially the cost of the technology will be closer to $1,000 than $10, but over time Donelan thinks that will shrink dramatically. Farther down the road, he sees the technology helping provide a "better quality of life for the developing world, where a half-billion children live without easy access to electricity."

Donelan is a big fan of the One Laptop Per Child initiative, but notes that children presently have to take breaks from their homework to generate electricity for their computers.

"The main thing that will prevent our technology from being used for this purpose in the near term is simply cost," he said. "The power source for a $100 laptop can't cost hundreds of dollars."