Optimizing orientation of piezoelectric cantilever beam for harvesting energy from human walking

Harvesting energy from human body motion for powering small scale electronic devices is attracting research interest in recent years. Piezoelectric energy harvester (PEH) capable of harvesting energy from vibratory movement is a suitable candidate for this particular application. In this study, a cantilever beam with a piezoelectric patch attached at the end of the cantilever is evaluated for potential to harvest energy from human motion. Since the frequency of human walking motion is low, the frequency up conversion technique is adopted in this study to harvest the inertial energy. The effect of orientation of the cantilever beam with tip mass on the efficiency of the power generated is experimentally studied. A prototype is developed and attached onto the leg of a person walking on a treadmill at a constant speed. A theoretical lumped model is adopted to predict the voltage output using the experimentally measured acceleration as input data. Results show close agreement between the experiment and the model. Results also indicate that by varying the orientation of the PEH, the efficiency of the energy harvester can be significantly increased. Maximum power is found to be achieved when the PEH is orientated at 70 with reference to a coordinate system attached to the leg when walking on a treadmill.