Reuters.com | Fri Sep 9, 2005 9:13 AM ET10
WASHINGTON (Reuters) - A backpack that converts a plodding gait into electricity could soon be charging up mobile phones, navigation devices and even portable disc players, U.S.-based researchers said on Thursday.
Their backpack design converts mechanical energy from up-and-down movement of the backpack's cargo to electricity during normal walking.
Fueled by a snack, hikers can put the spring in their steps
to good use, the researchers write in Friday's issue of the journal Science.
The backpack is deliberately designed to shake around a bit. The up-and-down movement of the backpack's cargo compartment against the frame of the pack turns a gear connected to a generator.
The simple magnetic coil generator is similar in principal to those seen in hand-cranked radios, flashlights that work after a rhythmic shaking and other devices.
Humping along just under 85 pounds (38 kg) of weight in the
backpack can produce up to 7 watts of electricity, Lawrence Rome and colleagues at the University of Pennsylvania report.
This is more than enough electricity to simultaneously power an MP3 music player, a personal digital assistant, night vision goggles, a handheld global positioning satellite navigation device, and a mobile telephone.
The not-so-graceful human gait is a big help in making the pack work, they reported.
Human hips rise and fall about 2 inches with each step and a backpack worn by a person who is walking rises and falls as well, they said.
"As humans walk, they vault over their extended leg, causing the hip to rise 5 to 7 centimeters on each step. Since the backpack is connected to the hip, it too must be lifted 5-7 centimeters," Rome said in a statement.
"It is this vertical movement of the backpack that ultimately powers electricity generation."
But nothing is free, so what does this energy cost the hiker?
Little more than a snack, said Rome.
"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."