Design of a New Piezoelectric Energy Harvester Based on Secondary Impact

Two models for an energy harvester imparting rotational energy to piezoelectric materials are presented, in order to compare the effects of applying identical amounts of energy to a cantilever beam by changing the total displacement per unit time, and applying a secondary impact. For a piezoelectric energy harvester given a high total impulse per unit time with low total displacement per unit time, higher power outputs were generated at lower resistive loads. Conversely, for a harvester given high total displacement per unit time with low total impulse per unit time, power output was higher at high resistive loads. At matched impedance, the secondary-impact-type piezoelectric energy harvester generated higher power output than the hitting-type piezoelectric energy harvester did at low resistive load. Optimized response of secondary-impact-type piezoelectric energy harvester was obtained at a frequency of 60Hz with a low resistive load of 1 k. The generated output power was measured as 124 mW, which corresponds to power density of 140 mW/cm(3) for the entire cantilever beam, and a power density of 342 mW/cm(3) for only the piezoelectric material volume (including sliver paste volume). For a harvester without a secondary impulse at low resistive loads (1 k), the optimizing frequency was between 20 and 30Hz, with an output power of 22 mW, which corresponds to a 25 mW/cm(3) power density for entire cantilever beam and power density of 60 mW/cm(3) for only the piezoelectric material volume(including sliver paste volume).