Development of piezoelectric and triboelectric generators that harvest the kinetic energy generated by movement has been gaining momentum over the past few years, and now the US Army and Marine Corps are taking the technology into the field. Vancouver-based Bionic Power will soon supply troops with its PowerWalk Kinetic Energy Harvester, a lightweight device worn around the knee that recharges batteries while soldiers walk.
The PowerWalk features a gearbox that mechanically converts the knee's rotation speed into a higher speed that is more efficient for the onboard power generator to then convert to electrical power. The result is 10 to 12 watts of electricity, which is itself then converted to charge Li-ion or NiMH batteries.
Wearing a PowerWalk on each leg, users can apparently generate enough electricity to charge four smartphones after an hour of walking at a reasonable pace. The PowerWalk is also able to analyze the wearer's gait to determine the most efficient time to generate power, and Bionic Power claims a secondary benefit of reducing muscle fatigue during downhill walking, lowering the risk of knee injury.
The applications for the military are clear. Electricity is vital in the field, with communications, navigation and optics devices all requiring power, which usually involves carrying heavy battery packs.
"A soldier typically carries 16 to 20 lbs (7 to 9 kg) in batteries on a 72-hour mission," says Noel Soto, US Army Systems Engineer. "If a soldier can generate power with wearable energy-harvesting devices, it means we can not only reduce the weight on his or her back, we also minimize the unit's reliance on field resupply, making it possible for us to extend the duration and effectiveness of a mission."
The contract between Bionic Power and the US Army and Marine Corps will see PowerWalk units tested in the field in early to mid-2017. Beyond that, Bionic Power hopes to bring the device to other professional and general consumer markets.