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Researchers have created a new knee brace device that can harvest energy normally dissipated or essentially wasted from the human body during walking.
While it's not shocking that power can be generated this way, it may be surprising to hear how much electricity the device can produce: five watts, enough to run 10 cell phones.
The journal Science first reported the news and scientific results of a study of the brace, which was created by researchers from Simon Fraser University in Burnaby, British Columbia; the University of Pittsburgh; and the University of Michigan.
Harvesting Wasted Energy
Unlike hand crank-based power generators, the new knee brace doesn't require much from the user -- in fact, the researchers who created the brace found that a human seems to expend less than one watt of energy wearing the brace while the brace harvests a full watt. No scientists have claimed to have messed with the laws of physics here -- energy from walking is going somewhere -- it's just that the brace is surprisingly efficient, they say.
"We really wanted to take advantage of the negative work that is being done by the hamstring in trying to decelerate or stop the leg, and that negative work is dissipated as heat, and rather than turning it into heat, we turn it into electricity or power," Yad Garcha, CEO of Bionic Power, told TechNewsWorld. Bionic Power is a new company formed to develop and market the device for commercial use.
Very Much a Prototype
While long-distance runners may dream of being able to charge their iPods while on the go, real-world use isn't quite ready for prime time. The knee brace is a prototype, and it needs a bit of work before off-the-grid users will be converting their own power to portable electricity.
"We want to reduce the weight and the size of it," Garcha said. "Right now, it's an off-the-shelf brace that we are using, but ideally we could use a brace with this product in mind, and as a result we are in discussions with some of the athletic brace manufacturers to design a very lightweight brace."
"We need to move the control system on board -- currently it resides on our PC," he explained. "Then we are trying to improve the sensors, so that we know when the subject is walking uphill, downhill, going up stairs or down stairs so that we can vary the amount of power that we are generating. At times we can generate more and sometimes we need to generate less. We want this to be very much in the background and passive, and the only way you can do that is to know exactly what kind of activity is involved."
In fact, the knee brace actually seems to help the wearers as their foot hits the ground, softening the effort required by the knee and the pressure on the knee during walking. Bionic Power believes that athletic brace manufacturers will be able to make the brace portion of the bionic knee even more ergonomic and comfortable for long-term use.
Forget the Batteries
One of the first places this new device may show up is on the battlefield. Military personnel carry pounds of disposable batteries for a variety of electronic gear. One study, Garcha noted, found that Canadian soldiers carry so many batteries that each soldier's battery use costs about US$57,000 per year -- and American soldiers use even more.
"The problem for the soldier is not just the cost, it is the weight -- it's a limiting factor for them," Garcha said. To reduce the weight, soldiers have to choose between taking less batteries for their devices, such as critical GPS 
(global positioning system) or communications units, or taking less food, water or ammunition -- none of which are good options.
Other uses may be to power prosthetic devices for disabled persons, provide power in off-the-grid developing nations, or for consumer applications for outdoor enthusiasts who are increasingly taking iPods, cell phones, GPS units and walkie talkies into the backcountry.
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