Design, Fabrication, and Characterization of Bimorph Micromachined Harvester With Asymmetrical PZT Films

This paper presents a high-performance bimorph MEMS cantilever harvester with partially covered asymmetrical functional piezoelectric layers on both sides of a beryllium bronze foil. The optimal PZT coverage length is employed to improve the output power density. The two piezoelectric layers with the controlled different thicknesses for the top and bottom PZT layers can provide three different output powers. Furthermore, a proof mass tungsten bonded at the free end of the cantilever can reduce the resonant frequency. The experimental results showed that the serial-connected bimorph piezoelectric energy harvester can obtain the maximum power density of 26.90 mW/cm3 at the matched loading resistance of 660 $\text{k}\Omega $ under 1.5-g acceleration at the resonant frequency of 38.89 Hz. The normalized power density of the harvester can reach $307.4\,\,\mu \text{W}\cdot \text{g}^{-2}\,\,\cdot $ cm $^{-3}$ . Meanwhile, the harvester provides good stability under 1.5-g acceleration amplitude.