Vibration-based energy harvesting using piezoelectric materials has gained considerable attention over the past decade. Currently, most piezoelectric energy harvesters (PEHs) are single resonance frequency based. The performance of a single-resonance PEH is often limited to only one resonance frequency. This paper discusses the possibility of improving the performance of a bimorph PEH by tuning the PEH using a spring-mass system attached to the bimorph’s free end. Through adding the spring-mass system, the PEH’s resonance frequency can be tuned to match the ambient vibration frequency, and its voltage/power-generating capability can be improved. An electromechanical model of the PEH is derived based on the Lagrange multiplier method. The model is then used in a harmonic base excitation case study, and the coupled electromechanical outputs are discussed. Simulation results show that the spring-mass attachment can create two resonant frequencies, making the PEH capable of working efficiently at two different frequencies in a low-frequency level. It is also shown that by properly selecting the spring stiffness and the mass, the voltage and power output of the PEH can be greatly increased as compared to a single bimorph without the spring-mass system.

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