Multi-factors analysis on the energy harvesting performance of PEH under multiple-frequency excitation

Abstract

The piezoelectric energy harvesters (PEHs) undergoing coupled bending-torsional vibrations were designed by crossbeam-offset and asymmetric mass, and the maximum output peak voltage at the first mode (Up-max1) and the minimum resonance frequency difference between the first and second modes (Δf0) were 81.5 V and 16.0 Hz chosen as the optimization objectives in the multi-factors analysis based on the orthogonal test method. The geometrical parameters including the crossbeam length, mass ratio, substrate thickness and primary beam length are correspondingly determined, before the PEHs were fabricated to investigate the optimum resistance and energy harvesting efficiency. The PEHs were constructed as the series connection structure, and the mechanical vibration experiments were performed to measure output peak voltage vs frequency curve. When the load resistance is applied from 47 to 1000 kΩ, all of the optimum resistances are about 470 kΩ for the PEHs with the offset ratio 1.23 and mass ratio 4. The errors are at the ranges of 5.0%–16.4% for Up-max and 1.1%–6.5% for f0, and the measurement reliability is acceptable. The sums of half-power bandwidths are regarded as the energy harvesting characteristic to evaluate the efficiency, and they are broaden by 133% and 180% for the PEHs with crossbeam-offset and asymmetric mass under multiple-frequency excitation. PEH undergoing coupled bending-torsion vibrations could harvest more electrical power at multiple resonance frequencies in nature environment.