Soldiers laden with modern electronics gear may soon reduce the number of batteries they lug by generating energy from walking.
An Arizona State University researcher is part of a team that has developed a backpack strap that produces power generated from motion.
The straps, which use a new elastic metallic polymer, produce energy without requiring more labor by the wearer than traditional straps, said Henry A. Sodano, a researcher in ASU's Adaptive Intelligent Materials Systems Center.
Even though lightweight, superstrong, Space Age materials are increasingly used in military field gear, soldiers often carry more than 100 pounds on their backs. A good part of that weight comes from modern gear that soldiers didn't have to deal with in the past — GPS units, radios, satellite links, laptop computers, infrared goggles and lighting — not to mention cell phones and i-Pods. And, of course, the batteries, and extra batteries, to power that equipment.
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"They carry between 15 and 20 pounds of batteries," Sodano said. "The real goal was to reduce that amount." Sodano said the new system was developed with support from the Office of Naval Research, which is seeking alternative energy sources for Marines.
There have been some other attempts to capture ambient or wasted energy, Sodano said. One involved shoes that generated power from the compression of the soles. But Sodano said he heard they were rejected because they increased the wearer's effort, as if walking in sand — hardly the thing to do to a soldier already carrying 100 pounds of gear.
Another approach used a backpack that moved up and down on a geared rack as the wearer walked, generating power. But Sodano said it wasn't efficient, returning less than half the energy it took to power it.
The straps Sodano's group created produce electricity — between 20 and 100 volts — using the piezoelectric effect. Piezoelectric is the term for materials that produce electric current when pressure is applied to them. Gas-grill lighters and cheap microphones are devices that use piezoelectric power generation.
The research on capturing waste motion as energy could have civilian applications, too, Sodano said.
"There's a lot of energy in your body that could be converted into electrical energy," Sodano said.
He said energy could even be captured directly from human bodies, from heartbeats or the expansion and contraction of a rib cage.
Sodano said the amount of power produced by the straps is small, even with a 100-pound pack: enough to power an i-Pod or a cell phone on standby. But he said someone hiking all day could store enough energy to power a highly efficient LED light at a campsite each night.
The research team recently published its results in a report in the engineering journal Smart Materials and Structures. The report's lead authors were grad students working with Sodano while he was at Michigan Technological University.
