A novel two-degree-of-freedom nonlinear piezoelectric energy harvester with a stopper for broadband low-frequency vibration

Energy conversion efficiency and operation bandwidth are two main concerns in piezoelectric energy harvesting in low-frequency vibration environments. This paper presents a compact two-degree-of-freedom nonlinear piezoelectric energy harvester (2DOF NPEH) with a stopper. The proposed harvester consists of an elastic beam, a piezoelectric beam with tip mass, a pair of repulsive magnets, and a mechanical stopper. A bistable configuration is established through magnetic interaction. This study investigates the generating characteristics of the 2DOF NPEH under frequency-sweep excitation, utilizing a rigid stopper (RS) and different elastic stoppers (ESs). The experimental results indicate that the implementation of a mechanical stopper in a NPEH contributes to widening the operation bandwidth and enhancing the peak voltage. As the stiffness of the stopper increases, the bandwidth gradually shrinks while the peak voltage increases. The optimal energy conversion efficiency depends on the stiffness of the ES, and it occurs when the wire diameter of the spring is 1.2 mm. Compared with the 2DOF NPEH without a stopper, the utilization of a RS results in a 13.85-fold increase in the bandwidth of the generator at the first resonance. Moreover, the maximum absolute voltage is 12.82 times and 3.47 times the output voltage of the 2DOF NPEH at the first and second resonance, respectively. This work offers valuable insights into the design and optimization of piezoelectric energy harvesters in practical applications.