No power for cellphone? Just walk a few blocks

People power has taken a big step forward with a Canadian invention that harvests energy as you walk.

Strolling along with one of the devices strapped to each knee generates enough power to run 10 cellphones, or a couple of small computers.

That is without even breaking a sweat. "With a modest increase in effort you get enough for 30 cellphones, or 30 minutes of talk time for a minute of walking," says kinesiologist Max Donelan, at Simon Fraser University, who heads the international team that has created the device for "harvesting people power." It so intrigued the editors of the journal Science they give a report on the device top billing in today's issue.

Mr. Donelan and his colleagues are also filing for worldwide patents and have spun off a B.C.-based company, Bionic Power, which launched its Web site Thursday to capitalize on the attention generated by the Science report.

The researchers don't expect people to be strapping on the devices to power their cellphones anytime soon, but they see plenty of military and medical applications.

They also dream of giving youngsters in the developed world access to computers even if they don't have electricity.

"When their laptop starts to run out of juice, they‘d have to run outside and play," Mr. Donelan said in an interview.

So far, there is only one custom-built set of the devices.

Volunteers have been putting them through the paces on a treadmill in Mr. Donelan's lab. The results show that simply walking along generates about five watts of electrical power -- enough to run 10 cellphones at once. The power production goes up with the pace, with one speedy volunteer generating 54 watts of power.

The devices capture the mechanical energy of walking and transform it into electricity, much the way hybrid cars recharge batteries when you step on the brakes.

"Walking is a lot like stop-and-go driving," says Mr. Donelan, noting how the legs accelerate and decelerate with each step. The trick is to capture the energy as the leg slows down.

The device has a real-time control system that measures knee angle and velocity 1,000 times a second and "will decide" when best to engage and disengage the generator, says Mr. Donelan, explaining how it harvests energy from the end of a walker's step.

It takes so little effort that he says the volunteers don't even notice when the harvesters are turned on.

"Without them knowing we can engage the power generation and they'll start to produce power and they don't even realize it until we turn it off," says Donelan.

Measurements of volunteer's oxygen use and carbon-dioxide production shows that producing electricity does take a bit of metabolic power. But not much. And humans usually have energy to spare -- the average person stores as much energy in fat as a 1,000-kilogram battery, the researchers say.

Mr. Donelan specializes in the study of walking and says he first started thinking about the device about 10 years ago, when he first learned about an energy harvester designed for shoes. He recalls thinking the real power is not in the feet, but in the leg muscles. "If you want to get electricity, you go where the powerhouses are," says Mr. Donelan.

He and two colleagues, now at the University of Pittsburgh and University of Michigan, refined the idea. Then, Mr. Donelan and his graduate students built the prototype with a $125,000 research grant from the Natural Sciences and Engineering Research Council.

"It's a proof of concept," says Mr. Donelan. One that "definitely has drawbacks," he says, noting the device on each leg weighs about 1.6 kilograms.

The company Bionic Power aims to cut the weight in half and have 20 streamlined units ready for testing by next year.

Mr. Donelan hopes to convince the military to try the harvesters as a way of lightening soldiers' loads in the field. Batteries power everything from their GPS devices to night vision goggles.

He also see many medical applications such as powering robotics arms and prosthetic devices and extending the battery life of implanted insulin pumps. Eventually, Mr. Donelan says it might be possible to implant energy harvesters alongside the devices.