Researchers Develop Power
In addition to food, potable water, medical supplies, LED flashlights, radios and other electronic gear such as GPS satellite receivers, some crews -- rescue teams and National Guard soldiers, for example -- must carry other weighty tools while on duty.
Researchers say shouldering that load may someday be helpful in another way: To help produce electricity to run the workers' high-tech gear or to provide power in areas where there is none.
Researchers at the University of Pennsylvania have developed a new type of backpack that actually generates electricity as a load-bearer walks. Lawrence C. Rome, a professor at the university's Department of Biology and the lead researcher of the project, says the concept behind the device is pure simplicity.
"When you walk, your hips move about five to seven centimeters [about two to three inches] vertically," says Rome. "That's because you have a straight leg, that when you plant it on the ground, it's actually lifting you -- sort of like when a pole-vaulter plants his pole and then is lifted up -- in an arc as you move forward."
Most people don't notice those tiny up-and-down motions while walking. But Rome did and he set out with his research team -- Louis Flynn, an engineer, and postdoctoral fellows Evan M. Goldman and Taeseung D. Yoo -- to turn those small oscillations into pure electrical energy.
The plate bounces vertically in reaction to every step taken by the wearer. And as the plate moves, the "rack-and-pinion" setup turns the generator to create electricity.
Tests conducted by Rome's team show that the backpack not only works as predicted, but delivers another interesting feature.
"Electricity generation is proportional to the load you carry and the speed you walk," says Rome. "By either increasing the speed or the load, you can generate much more electricity."
Their results, published in the current issue of Science magazine, show that a person carrying about 40 pounds in the pack at the quick pace of approximately 3 mph can generate about 0.8 Watts, or 800 milliwatts, of power. But double the load and increase the speed to 4 mph and the pack will generate a whopping amount of juice: 7.4 watts.
"A cell phone uses 250 to 260 milliwatts of power, an brightest led flashlight, about 600 milliwatts, and a GPS receiver about 800 milliwatts," says Rome. "This is generating more electricity than a person is capable of using."