Knee-joint motion derived energy harvester using piezoelectric bimorph

Based on human motion, the knee joint has been selected as part of the energy harvesting device since it shows the high possibility to generate energy from its large motion. This work mainly uses the piezo ceramic bimorph cantilever as the energy harvesting sensor and the N35 MAGNET (3mm x 3mm x 3mm) for the magnetic plucking mechanism. Technique of magnetic plucking has been selected to overcome the low human frequency motion. Force from the magnet acting on the bimorph causing the bimorph to vibrate and then generate electricity. Two categories of magnet are used which consist of primary and secondary magnets. The primary magnet (PM) is mounted on the outer ring and the secondary magnet is fixed on the bimorphs. A prototype has been developed and later examined its performance. Power management module which is integrated circuit is used in managing the harvested energy from the bimorph. The modules consist of RC circuit to convert AC voltage to DC voltage and stepper motor controller to do demonstration of knee joint motion. The highest power successfully harvested from the prototype is 1.596 mW at the speed of 0.386 m/s and 115° angle of knee flexion.