Generate energy from backpack straps

Pic: The energy harvesting backpack uses piezoelectric straps to generate electrical energy. Credit: Jonathan Granstrom, et al.

The wonders of nanotechnology.
From physorg:

All that rubbing of your backpack straps on your shoulders may be put to good use, now that researchers have designed a novel type of energy harvesting backpack. The pack has straps made of a piezoelectric material that can convert the mechanical strain on the straps into electrical energy that may power or recharge portable electronics.

When carrying a 100-pound load—a typical amount for a solider’s pack—and walking at 2-3 mph, simulations showed that the straps could generate 45.6 mW of power. The researchers said that this power output could either be used to power small electronics, or be accumulated over the duration of an excursion to be used as a weightless supplemental energy source instead of carrying extra batteries. “Some devices that could be powered include an LED headlamp (~38 mW), an Ipod Nano (~46mW), and a Motorola Razr cell phone, which in standby requires ~9 mW of continuous powering and ~360 mW during talk mode,” Sodano said. “In general, we want to accumulate the power before using it so that we could walk for 20 minutes then talk for 2.5 minutes. Or you could charge an LED headlamp while you walk in the day and use it at night while you camp. The energy could also go toward powering a handheld GPS system, which requires ~165-200 mW of continuous power.”

The researchers teamed up with a company in Blacksburg, Virginia called NanoSonic, Inc., that provided a self-assembled nanocomposite material called “Metal RubberTM” to tailor an advanced electrode. Using nanotechnology to control its macroscopic properties, the researchers fabricated a 100-nm-thick electrode that could undergo strains of 1000% while maintaining conductivity, and then return to its original shape when released.

Citation: Granstrom, Jonathan, Feenstra, Joel, Sodano, Henry A., and Farinholt, Kevin. “Energy harvesting from a backpack instrumented with piezoelectric shoulder straps. Smart Materials and Structures. 16 (2007) 1810-1820.