clipped from: news.bbc.co.uk 
US and Canadian scientists have built a novel device that effortlessly harvests energy from human movements.
The adapted knee brace, outlined in the journal Science, can generate enough energy to power a mobile phone for 30 minutes from one minute of walking.
The new device generates power by a process known as "generative braking", analogous to the braking systems found in hybrid-electric cars such as the Toyota Prius.
"Walking is a lot like stop-and-go driving," explained Dr Max Donelan of Simon Fraser University in Burnaby, Canada, lead author of the paper.
The knee brace is the latest development in a field known as "energy harvesting".
The field seeks to develop devices and mechanisms to recover otherwise-wasted energy and convert it into useful electrical energy.
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