Backpack Pumps Power From Pedestrians

A biomechanics professor specializing in the movement of fish and frogs has invented a backpack that harvests electricity from the springy up-and-down motion generated by walking.

The backpack, which glides vertically as much as 2 inches on a sled-like frame, can generate as much as 7.4 watts with each step when carrying a 44-pound load.

The vertical movement turns a gear that creates an electrical current by moving a wire coil in and out of a magnet. The electricity can then be used immediately or stored in a lightweight battery. To minimize the strain on users, springs limit and cushion the backpack’s motion.

The backpack produces enough electricity to simultaneously power an MP3 player, a personal digital assistant, night-vision goggles, a handheld global positioning satellite receiver, a digital bar-code reader and a cellphone.

University of Pennsylvania biology professor Larry C. Rome, who reported his invention in Friday’s issue of the journal Science, said future versions of the backpack could significantly reduce the number of battery packs now required to run the gadgets that have replaced the Swiss Army knife as must-have tools for soldiers, hikers, field scientists, disaster relief workers and others.

Rome began musing about the power backpack in the 1990s after the Pentagon asked him to find a way to reduce the 20 pounds in spare batteries that soldiers had to carry.

“Metabolically speaking, we’ve found this to be much cheaper than we anticipated,” Rome said. “The energy you exert [carrying the backpack] could be offset by carrying an extra snack, which is nothing compared to the weight of extra batteries.”

In an accompanying editorial, Arthur D. Kuo, an engineering professor at the University of Michigan, said the backpacks could become popular accessories.

“In the developed world, many people seem more concerned with their cellphone battery life than with their next meal,” Kuo wrote.