Gizmo straps to knee, harvests energy from walking

An energy-harvesting gadget designed to strap to a person’s knee and charge from a walking motion is being hailed as a potential solution to ridding the world of batteries.
The next-generation device was introduced on Friday by British scientists in the journal Smart Materials and Structures, and could have useful applications for soldiers, who often have to haul power-generating equipment that can weigh up to 10 kilograms while on foot patrol.
Heart rate monitors, pedometers and accelerometers are among the kinds of tools that the knee-mounted gizmos could power, scientists say. Future models of GPS trackers could also be powered by the wearable devices.
Researchers from Cranfield University, the University of Liverpool and University of Salford were credited with the invention.
It would be a circular device that can strap onto the outside of the knee. A ring mechanism would rotate during a wearer’s natural gait, with the motions triggering a smaller “hub” ring connected to 72 plectra — small mechanical pieces that would pluck energy-generating arms on the device.
The vibrations from the arms would create electrical energy.

‘Bimorphs’ convert mechanical energy

Michele Pozzi, lead author of the study, explained in a release that the energy-generating arms are known as bimorphs.
“A bimorph is a type of piezoelectric device capable of converting mechanical energy, such as the vibrating caused by the plectra, into electrical energy, and vice versa,” he said. “Piezoelectric materials have long been used as sensors in SONAR and ultrasound scanners and have recently been the focus of attention in the field of energy harvesting.”
Prototypes of the device are currently able to harvest around two milliwatts of power — roughly the amount of energy emitted from some CD-rom laser beams. With some small adjustments, however, scientists say it could exceed 30 milliwatts of power, which could power future GPS tracking machines and allow for more frequent and longer wireless transmission.
“There is an on-going project looking at manufacturing a more compact and truly wearable harvester,” Pozzi said in a release.
He added that manufacturing the device could be cost-effective.
“I’d put a cost tag of less than £10 (Cdn $15.91) for each harvester on a large scale production,” he said.