WASHINGTON - As soldiers, hikers and students can testify, it takes energy to haul around a heavy backpack. Now, researchers have developed a backpack that turns that energy into electricity.
It doesn't crank out a lot of juice - just a bit more than 7 watts - but that's enough to run things like an MP3 player, a personal data assistant, night vision goggles, a handheld global positioning system or a cell phone.
The development could eventually allow field scientists, hikers, explorers, soldiers and disaster workers to produce their own electricity.
The researchers used a backpack fastened to the carrying frame by springs. The up-and-down motion caused by walking powers a small generator, producing electricity that can be used directly or stored in a capacitor or battery.
The device, developed by Lawrence C. Rome of the University of Pennsylvania and some of his colleagues, is reported in today's issue of the journal Science.
The electricity-generating frame weighs about 10 pounds, Rome said. He said he's working to lighten it.
Rome developed the backpack at the request of the Office of Naval Research, which was looking for ways to reduce the need for service members to carry lots of batteries.
The researchers studied the movement of people walking, and concluded that the hips move up and down between 1.6 inches and 2.7 inches with each step.
They then set about trying to exploit that movement.
The result is the "suspended load backpack." It uses a rigid frame similar to regular backpacks, but instead of being attached directly to the frame, the load is suspended by springs, allowing it to move up and down as the person walks. That movement turns a small electrical generator producing current. Arthur D. Kuo of the University of Michigan's Department of Mechanical Engineering and Biomedical Engineering said the backpack is novel because it generates useful amounts of electricity without taxing the wearer.
"Metabolically speaking, we've found this to be much cheaper than we anticipated. The energy you exert could be offset by carrying an extra snack, which is nothing compared to weight of extra batteries," Rome said. "Pound for pound, food contains about 100-fold more energy than batteries."