Capitalizing on the friction and heat created by walking, running and even just wearing jeans, engineers from Michigan Technological University, Arizona State University and NanoSonic Inc. devised a way to use this type of generated energy in a concept backpack that can charge portable electronic devices, like iPods and mobile phones.
Shoulder straps made of polyvinylidene fluoride (PVDF), a strong, flexible material that feels similar to nylon, are piezoelectric, which means that an applied stress generates an electrical charge (just like when you rub your feet on the carpet and shock your baby sister). Converting otherwise wasted, ambient energy into electrical energy, there's virtually no difference in the feel or characteristics of PVDF versus normal nylon. Now, all the rubbing of your backpack straps on your shoulders could finally be put to good use and you can leave heavy batteries and bulky chargers at home.
Expect to see this new design in soldiers' backpacks in the near future. A little further down the line we could be seeing such energy-harvesting systems integrated into our more normal line of outerwear.
Also on Cool Hunting: Power Pack