Impact of Geometry on the Performance of Cantilever-based Piezoelectric Vibration Energy Harvesters

This paper aims at comparing micromachined cantilever structures with the purpose of providing design guidelines towards high performance energy harvesters such that they provide a good output power, resonant frequency and volume tradeoff, while considering microfabrication process limitations. Increasing the power output of piezoelectric energy harvesters by tapering the beams has been presented as promising solution in the literature. This paper investigates the power output of several geometric variations of cantilever beams, and examines the advantages of balancing the strain distribution throughout the beam. A comparison of the impact of different geometries is presented, and recommendations are given. Namely, eight rectangular and trapezoidal T-shaped designs are fabricated and benchmarked. Their resonant frequencies and power outputs are compared for the same available area ( $1800\,\,\mu \text{m}\times 800\,\,\mu \text{m}$ ). Measurements show that the trapezoidal designs can have a higher output power depending on the beam length to mass length ratio, in comparison to the rectangular T-designs that have lower frequencies. Resonant frequencies ranging from 2.9 to 7.2 kHz and power outputs ranging from 2.2 to 7.1 nW are reported.