Numerical Model of a Non-Contact Piezoelectric Energy Harvester for Rotating Objects

Energy harvesting is an attractive technique for powering wireless sensors and low power devices. Harvesters delivering sufficient power from rotation for sensor applications have been developed, but difficulties are encountered when the devices to be powered are located off-axis on a rotating object. In such cases, harvesters are not adapted to low frequency and high amplitude of motion, where the input force amplitude is higher than the mass available displacement. A novel approach, based on using non-contact piezoelectric energy harvester to generate power from magnetic forces due to the effect of the centripetal force is proposed in this paper. In this approach, the pre-stressed piezoelectric beams are deformed by interaction with an oscillating magnet that is supported by magnetic levitation system. Because the magnetic levitation system is nonlinear, the nonlinear spring enables operation over a wide range of large centripetal accelerations. A model of the system is presented and analyzed in order to identify the parameters that control the performance of the harvester. Theoretical investigations are followed by a series of experimental tests to validate the response predictions. With an off-axis distance of 75 mm the prototype, occupying a volume of approximately 17.74 cm³ and weighting 46 g, generated an output power ranging from 0.2 μW to 3.5 μW when the rotating speed changes from 3 rps to 5.55 rps. Further optimization of the piezoelectric harvester is carried out in order to improve the power density. An application in which the harvester can be used in is tire pressure monitoring systems. In this case, the harvester can replace the battery of the pressure sensors located inside the vehicle tire.