Harvesting Energy From a Rotating Gear Using an AFM-Like MEMS Piezoelectric Frequency Up-Converting Energy Harvester

This paper presents an analytical and experimental study of a compact configuration to harvest energy from a rotating gear using piezoelectric microelectromechanical system harvesters. The reported configuration realizes a contact-type frequency up-conversion mechanism in order to generate useful electrical energy. The up-conversion mechanism was achieved using an atomic force microscope (AFM)-like piezoelectric cantilever plucked by the teeth of the rotating gear that could be eventually driven by an oscillating mass. This paper describes relevant design guidelines for harvesting energy from the low-frequency mechanical movement of a rotating gear through analytical modeling and finite element method (FEM) simulation followed by experimental validation. Different harvester configurations are investigated to identify the optimal configuration in terms of the output energy and energy conversion efficiency. The latter results are reported for the first time because of the implementation of an original concept based on the coupling of the harvester with a rotational flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the output energy and efficiency. By adding a proof mass, the efficiency of the system can be greatly improved. For plucking speeds between 3 and 19 r/s, average output powers in the order of tens of microwatts were obtained for continuous plucking. By combining interaction energy, friction, and energy absorption, between the harvester and inertial mass, the maximum efficiency of the impact piezoelectric harvesters was found to be 1.4%. The efficiency results obtained were compared with the noncontact magnetic plucking approach further demonstrating the potential of our concept. Finally, different tip-gear materials combinations were evaluated showing the importance of their nature on the reliability of the presented configuration.