Low-frequency Zigzag energy harvesters operating in torsion-dominant mode

Natural frequencies and mode shapes of low frequency (<100 Hz) Zigzag piezoelectric energy harvester with torsion-bending characteristics are theoretically derived and experimentally validated. Two- and three-dimensional computational finite element models are developed to provide fundamental insight into understanding the response of such harvesters. The optimal harvested power from higher order modes is experimentally determined and computationally verified. It is shown that despite the first mode being a torsion-dominant mode, it can provide a higher level of harvested power compared to the second mode, which is bending-dominant. It is also proven that the torsion-dominant mode may decrease the operating frequency by 50%, compared to the bending-dominant mode, allowing the harvester to output greater power at lower excitation frequencies. This is contradictory to the conventional thought process where torsional modes are generally avoided. The results open new opportunities to further lower the operating regime for known piezoelectric energy harvesters without any significant increase in dimensions or decrease in performance. An analytical model using Gauss's law is developed to relate the output voltage to the structure's deflection. Using this model, a prediction of the harvested power can be performed when studying the steady state behavior of the system.