A new prototype device has been reported to the journal Science by Max Donelan and colleagues at the University of Pittsburgh and the University of Michigan.The device generates electrical power from the swing of a walking person's knee. With each stride the leg accelerates and then decelerates, using energy both for moving and braking.It's sort of like the way that some hybrid-electric cars produce electricity from braking.
With the device, a minute of walking can power a cell phone for 10 minutes. There are other potential uses being considered for the devices, these include powering a portable GPS locator, a motorized prosthetic joint or implanted drug pumps.The device weighs about 3.5 pounds so users do burn energy carrying it on their knee and with one generator on each knee, people walking on a treadmill were able to generate about 5 watts of power according to the report.The device considering the potential, will be further developed and improved to make it easier to carry and comfortable for the user.