Hybrid Piezoelectric-Electromagnetic Cut-Out Energy Harvester with Adaptive Potential Wells: Design and Nonlinear Modeling

Purpose: This paper presents a novel bistable, multi-frequency hybrid energy harvesting mechanism with an adaptive potential barrier, aimed at improving energy scavenging efficiency in low-excitation environments. 

Methods: The system employs a recently developed bistable two-degree-of-freedom cut-out piezoelectric harvester, which achieves substantial power output through two closely positioned resonances. However, conventional bistable harvesters underperform when the excitation level is insufficient to overcome the potential barrier. To address this, an auxiliary magnetic oscillator is incorporated into the original cut-out harvester to lower the barrier dynamically and facilitate inter-well oscillations. Also, an induction coil surrounding the magnetic oscillator scavenges extra electrical power, further enhancing the overall power generation. The mathematical model is derived through a hybrid procedure combining the Ritz method with the Euler-Bernoulli beam and magnetic dipole theories. The model accuracy is validated by the available experimental observations for simpler systems. Furthermore, a bistability criterion is introduced, outlining the system properties required to trigger inter-well oscillations. 

Results: Numerical results demonstrate that the proposed harvester overcomes the potential barrier at lower excitation amplitudes and achieves higher generated power over a broader frequency bandwidth. Under a 4.5 m/s^² excitation, the hybrid harvester generates a maximum average power of approximately 12 mW, representing a 118% improvement over the conventional design. 

Conclusion: The analyses confirm that the proposed hybrid design significantly improves energy harvesting efficiency compared to conventional designs reported in the literature.