We’ve seen energy-harvesting devices for the human body before, from run-of-the-mill kinetic watches to backpacks that use a bouncing 50-pound load to produce power, but a knee brace that generates electricity from walking is something entirely new. Researchers at the University of Michigan recently developed the device as a proof of concept, but in the future it could be used to charge everything from laptops to cell phones without ever needing to plug in to the grid.
The brace captures energy that would normally go into “braking” the human body during ordinary walking, and converts it into electricity. While the aforementioned gadgets have managed to pull off similar feats before, the team’s real accomplishment was the efficiency the knee brace operates with. According to the researchers, the device actually generates more than a watt of electricity from less than a watt of extra metabolic power – the extra energy a human body puts into walking with the device strapped on. This is possible due to the knee’s role as a shock absorber: since a certain amount of metabolic energy is wasted in ordinary walking to soak up impact, allowing the device to harvest that energy means some “free” electricity is harvested without a corresponding cost in extra human power. Ordinary human-powered generators, like hand-crank generators, require an average of 6.4 watts of metabolic power to produce just one watt of electricity.
“The prototype device is bulky and heavy, and it does affect the wearer just to carry. But the energy generation part itself has very little effect on the wearer, whether it is turned on or not,” said Arthur Kuo, a mechanical engineering professor who helped develop the brace. “We hope to improve the device so that it is easier to carry, and to retain the energy-harvesting capabilities.”
Besides holding some potential for consumer use, the team envisions hikers and soldiers drawing power from a more refined version of the device, along with those who need to power implanted medical devices like pacemakers.