human power | Science Buzz

Biomechanical Energy Harvester: In the very near future, taking a brisk walk may not only recharge your batteries but will also recharge your cell phone and iPod batteries.
Courtesy Simon Fraser UniversityOur man Thor recently posted a story about an energy-producing fabric that in the near future will enable you power an iPod or other electronic device just by wearing it, like as a shirt or maybe underwear. But it sounds like you’d have to do a heck of a lot of moving around just to get it to power a single phone call. And to tell you the truth, it looks pretty itchy to me, and would probably shrink in the wash. So personally, I’d much prefer having something strapped to my knees that harvests the energy created by my walking or running, and use that to charge my favorite electronic gizmo.

Well, now I guess some engineers in Canada and the U.S. have developed just such a device: a modified knee brace that harvests energy expended while you walk. And instead of a measly 80 milliwatts of electricity (like a square meter of the fabric would produce), this device can produce something like 5 watts! The team, which included researchers from the University of Pittsburg and the University of Michigan, published their findings in the journal Science.

The device is called the Biomechanical Energy Harvester, and what's cool is the way it captures the energy. While a person’s walking, it turns itself on and off at critical moments during the stride in order to gather the energy while the user’s leg is involved in what’s termed negative work. That’s when the leg has completed its swing forward and its foot is on the ground decelerating while the other leg is beginning the positive work of swinging forward.

"If you want power, go where the muscles are," said Max Donelan, professor of kinesiology at Simon Fraser University, in British Columbia. "We thought, maybe there's a smart, selective way to do energy harvesting when muscles are normally decelerating in the body."

The brace then switches off just as the leg begins its positive work again. If it didn’t do this the device it would hinder the forward motion of the leg.

“That engagement and disengagement happens once the stride is at the region where your muscles need the help at the end of the swing phase. It actually assists them in decelerating that extra resistance,” Donelan said.

At the same time, the gadget is also producing electricity. It’s similar to how a hybrid automobile charges its batteries while braking. You can see the brace in action here.

Right now the prototype is cumbersome and weighs in at about 3.5 pounds but a lightweight version could be available within the next 18 months. Donelan, who led the research, thinks the brace could have applications in the medical field, and also be used by hikers or soldiers to power GPS devices or satellite telephones where no other source of electricity is available.

With a brace on each leg, the user could generate up to 13 watts of electricity depending how fast they moved. To put it in more practicable terms, a one-minute stroll wearing the bionic knee brace could harvest enough energy to power a ten-minute cell phone call.

New energy source?: Wildcatters may soon be turning their attention to kneecaps.
Courtesy euthmanGoodness gracious, just think of all the megawatts of electricity that could be harvested at the Boston or New York Marathons each year. It could mean the antiquated term “horse power” may soon be replaced by “knee power”.