Nonlinear broadband piezoelectric vibration energy harvesting enhanced by inter-well modulation

Broadening the working bandwidth of piezoelectric energy harvesting devices is of great importance owing to the wide frequency spectrum of environmental vibrations. Efforts, including stiffness nonlinearity and multimodal optimization, have been proposed to improve harvesters' responses towards the broadband frequency region. This paper designs a spring-based bistable energy harvester (SBEH) and proposes its two configurations (SBEHsup and SBEHsub) to achieve high working efficiency under different excitation levels through inter-well modulation. The nonlinear force produced by the compressed springs generates nonlinear dynamical responses, and thus broadens the effective bandwidth of the SBEH. Compared to the SBEH-sup configuration, the SBEH-sub configuration further utilizes magnetic force to dynamically alter the potential energy threshold in the nonlinear system, which contributes to the SBEH maintaining inter-well motion and enhancing the working performance under lower intensity excitation. The working mechanisms of the SBEH-sup configuration and the SBEH-sub configuration are revealed by derived mathematical models. The feasibility of the SBEH with two proposed configurations is verified by experimental tests. Compared with its linear counterpart, the significant advantages in the SBEH-sup configuration show 673% increment in effective bandwidth and 179% increment in working efficiency under suprathreshold-level excitation. Compared with the SBEH-sup configuration, the SBEHsub configuration further broadens the operating bandwidth by 838% and enhances the working efficiency by 269% under subthreshold-level excitation. This spring-based bistable energy harvester provides a new design philosophy for nonlinear energy harvesters, its two configurations with inter-well modulation achieve satisfactory performance for scavenging energy from different-level vibrations.