Design and characterization of a self-excited unibody piezoelectric energy harvester by utilizing rotationally induced pendulation of along-groove iron balls

Energy harvesting from rotational motion by using piezoelectric transduction has attracted considerable attention to enable the energy-autonomous structural health monitoring systems of rotating machines. Unlike most existing separated-type magnetically plucked piezoelectric rotational energy harvesters (PREHs) where an extra stationary support is frequently required to install magnets, a self-excited unibody PREH was proposed to harvesting energy from rotating machines. To verify the structural feasibility and figure out the effect of along-groove iron balls on the dynamic characteristics and power generation performance of this PREH, theoretical analysis, simulation, fabrication and experimental testing were performed. The results showed that the exciting and structural parameters brought significant impacts on the generated voltage and output power. Besides, unlike traditional PREHs with multiple wave crests, there was no an obvious voltage peak under various experimental rotating speed responses of this PREH because of the random excitation of the iron ball. Hence, this PREH could obtain a relatively stable electric output within a broad effective rotating speed range. Finally, the load resistance-dependent power indicated that this PREH prototype with two iron balls could yield a maximum output power of 6.4 mW at 40 kΩ and 780 r/min and 50 blue LEDs could be lighted by it.