Piezoelectric Backpack Concept: Take a Walk, Charge Your Gadgets
All that rubbing of your backpack straps on your shoulders may now be put to good use, thanks to straps made of piezoelectric fabric that can convert the friction on your shoulders to electric energy. If solar-powered bags aren't your thing, engineers from Michigan Technological University, Arizona State University and NanoSonic Inc. have you covered, having developed a concept backpack that "harvests" the energy created by the friction of a bouncing backpack.
The straps, made from polyvinylidene fluoride (PVDF) -- a strong, flexible material that feels similar to nylon -- generate an electrical charge from applied stress, sort of like when you rub your feet on the carpet and shock your little brother; in this case, though, the energy can be used to keep rechargeable gadgets like iPods and cell phones charged up. The developers estimate that when shouldered with a 100 pound load -- a typical pack weight for soldiers, for whom the pack was first devised -- and walking at 2-3 mph, the straps could generate 45.6 milliwatts (mW) of power. This power output could either be used to power small electronics, or be accumulated in a small battery pack; some devices that could be "plugged in" to the pack are 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.
According to Henry Sodano, one of the device's developers, from Arizona State University, "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." So long, bulky chargers and heavy batteries.
The military is likely to get the first crack at this technology, while developers continue to work on integrating piezo textiles into other conventional outerwear; imagine what sort of fun you could have with a combination piezo/solar backpack! For more piezoelectric action, check out Japan: Producing Electricity from Train Station Ticket Gates and Solar Powered Retinal Implants. ::Physorg via ::Cool Hunting