Thursday, March 27, 2008

Finding Energy All Around Us

You won't feel comfortable or fashionable walking around with Max Donelan's invention strapped to your knee. The bulky 3.5-lb. (1.6 kg) gadget "is not that pleasant," says Arthur Kuo, a biomedical engineer at the University of Michigan, who co-wrote an article on the brace that appeared in Science last month. But Donelan's device pays off in other ways. Using the same principles that allow hybrid cars to recycle energy created in braking, braces worn on both knees can generate 5 watts of electricity by harvesting the energy inherent in a walker's stride. That may not sound like much, but it's enough to charge 10 cell phones, and it's absolutely free. "People like the idea of generating their own power," says Donelan, a kinesiologist at Simon Fraser University in British Columbia. "If you do things in a clever way, you can get energy cheaply."

Getting energy cheaply has never been more necessary than it is now, with oil recently breaking its all-time inflation-adjusted high price. The era of inexpensive power is over, perhaps for good, which means it's time to extend beyond energy efficiency to energy-scavenging, harnessing the sort of wasted watts we wouldn't have bothered with in the past. Fortunately, scientists are finding new ways to harvest unused energy from the environment, industrial activities and even the heat and motion of our bodies. "Energy-scavenging has been around for years, but because of the fuel crisis, everyone from big companies to small ones is looking to utilize it," says Marc Poulshock, president of Thermo Life, which produces devices that can harness thermoelectric energy. "It's a very hot topic."

One of the most abundant forms of unused energy in the environment is the vibrations that are a by-product of motion. Think of the rumblings of a bridge in heavy traffic or even the pulse of a dance floor. That's essentially free movement, and scientists can transform that micromotion into electricity in a number of ways. One should be familiar from high school physics class. A magnet hooked up to be sensitive to vibrations wobbles inside a copper coil, generating a current through electromagnetism. Steve Beeby, an engineer at the University of Southampton in Britain, created a vibration harvester that works on that principle much more efficiently than similar devices did in the past. The electricity isn't much: his devices now generate hundreds of microwatts at most, and there may be an upper limit to how much energy can really be scavenged from vibrations. "It's very unlikely on a big scale," says Beeby, who directed the European Union's Vibration Energy Scavenging project. "It will never compete with wind power or anything like that.",9171,1720111,00.html

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