<http://schema.org/about>
"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"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.treehugger.com/renewable-energy/piezoelectric-backpack-concept-take-a-walk-charge-your-gadgets.html>