By RANDOLPH E. SCHMID, AP Science Writer
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 GSM cell phone.
The development could eventually allow field scientists, hikers,
explorers, soldiers and disaster workers to produce their own
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 colleagues, is reported in Friday's issue of the
The electricity-generating frame weighs about 10 pounds, Rome said in
a telephone interview. He's working to lighten it, so it will weigh
only a couple of pounds more than a standard backpack.
Power generated increases as the load in the backpack gets heavier, he
said. Tests ranged from loads of about 40 pounds to about 80 pounds.
Rome developed the new 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 to power equipment while on duty in
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
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. In tests on a treadmill, walking on level
ground and uphill both produced current, Rome said.
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 electrical power, while
costing less metabolic power than would be expected."
Indeed, carrying the backpack uses only a little more energy than
carrying a standard backpack of the same weight, said Rome, a
biologist who also does research at the Marine Biological Laboratory
in Woods Hole, Mass. He said volunteers testing the device altered
their gait slightly to move more efficiently.
"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
The concept resembles that of a self-winding watch where power is
generated by the movement of the wearer, commented Kuo, who was not
part of Rome's research team.
The research was funded by the National Institutes of Health, Office
of Naval Research and the University of Pennsylvania Research
A company called Lightning Packs LLC has been formed to improve the
suspended-load backpack and to develop an ergonomic backpack based on
the prototype. Lightning Packs has applied for patents on both
Rome said he hopes to have the new version ready for testing in six
months to a year.
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Copyright 2005 The Associated Press.
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