"Suspended-load" backpack. The pack frame is fixed to the body, but the cargo compartment is suspended with springs from the frame. During walking, the cargo compartment rides up and down. To generate electricity, researchers attached a green toothed rack to the "load plate" of the backpack. When this toothed rack moved up and down during walking, it meshed with a gear mounted on a generator which generated electricity. Image © Science.
Scientists have invented an energy-harvesting backpack that generates useful amounts of electricity from the up and down movements of its cargo compartment.
Future versions of this backpack could allow disaster relief workers, explorers or soldiers to go out into the field with fewer heavy replacement batteries for cell phones, GPS instruments, night vision goggles and many other portable electronics. Refinements of the design could also lead to backpacks that are more comfortable and perhaps better for the back.
Human hips rise and fall about five centimeters with each step and a backpack worn by a person who is walking rises and falls as well. The new backpack converts mechanical energy from the vertical movement of the backpack's cargo to electricity during normal walking. The vertical movement of the backpack's cargo compartment (with respect to the pack's frame) turns a gear connected to a generator at the top of the pack.
Turning this gear leads to the production of electricity via the turning of coils of wire within a magnetic field inside the generator. A weight of 38 kilograms produces up to 7 Watts of electricity.
In a related "Perspective" in the 9 September 2005 issue of the journal Science, Arthur Kuo suggests an explanation for how the backpack harvests electricity with only a relatively small increase in metabolic cost as compared to the cost of wearing a regular backpack of the same weight.
Science subscribers can read the article here. The related Perspective can be found here.
See also a video of the backpack in action.
8 September 2005