Rucksack generates electricity, lightens troops' loads.

• Author: Jean, Grace V.
• Position: INSIDE: SCIENCE + TECHNOLOGY

* Anyone who has tried running while wearing a backpack knows how cumbersome a small load can become even after a short distance.

On the battlefield, troops carry as much as 80 pounds of battle gear and they lug an additional 20 to 30 pounds of batteries to power their portable electronic devices. That weight is so problematic that "lightening the load" has become the ground forces' mantra. But efforts to reduce weight have been stymied in part because troops need sufficient power for their equipment--energy that only comes from heavy batteries.

Finding a way around that conundrum has been a technological challenge. But researchers at the University of Pennsylvania have developed a rucksack that may soon allow troops to not only charge up their radios, night vision goggles and GPS units on the move, but also ease the weight problem.

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Based upon a standard rigid-frame pack carried by hikers, the electricity-generating backpack produces power from the mechanical energy created by a person walking or running.

If troops are carrying 80 pounds of equipment on their backs, the energy that goes into lifting that heavy load is 40 watts of mechanical energy, says Larry Rome, a professor of biology at the university who developed the technology with a grant from the Office of Naval Research.

"If we can capture a small amount of movement as they step and walk and lift the load, then we should be able to generate much more electricity than we ever have before," he says.

When a person walks, the body bounces up and down about two to three inches. A backpack, including the contents, also moves the same distance.

For the electricity-generating backpack, university researchers have separated the cargo compartment from the backpack's frame. Using springs, the compartment is suspended from the frame, which allows the load to move up and down at a slightly different pace. The load's movement turns gears located on the frame, which connect to a generator that produces the electricity.

"The more load you carry and the faster you move, the more electricity you can generate," says Rome.

The latest version of the backpack can generate 20 watts of electricity. Most of the portable electronics used by the military operate on less than half a watt of electricity.

"Our device will power equipment in real time," says Rome, who founded the company Lightning Packs LLC, to continue with the development. Any excess energy can be collected and stored...