Enhanced broadband performance of magnetically coupled bistable energy harvester with barrier-decreasing effect

A high potential barrier is not conducive to triggering the snap-through motion of a bistable oscillator. The magnetically coupled bistable energy harvester with multiple degrees of freedom, which possesses a considerable bandwidth due to its high-order resonances, also faces the same issue. To address this challenge, a novel magnetically coupled bistable energy harvester with a barrier-decreasing effect is proposed in this study to further enhance the performance in working bandwidth and power generation. The characteristics of co-bistability and variable barrier are skillfully realized by a pair of orthogonal spring oscillators facing a piezoelectric cantilever beam. Firstly, a mathematical model of the harvester is established based on the Euler-Bernoulli beam, linear piezoelectricity, and magnetic dipole theories. Subsequently, the system's static and dynamic bifurcations, decreasing barrier mechanism, and dynamic responses under swept and stochastic excitations are deeply investigated through numerical simulations, and the key parameters are optimized by intelligent optimization algorithms. Finally, a comprehensive test platform is constructed and the effectiveness of the designed harvester is validated through corresponding experiments. The simulation analyses show that compared with the conventional magnetically coupled bistable energy harvester, the presented harvester can reduce the barrier height by 65%, resulting in an enhancement in effective bandwidth of up to 108%. The power output capacity of the optimized MCBEH-BD is extremely improved under the white-noise excitation. Furthermore, it is found that the experimental results are qualitatively consistent with the numerical outcomes, and they all support the conclusion that the diminution of the potential barrier greatly increases the probability of inducing the potential well escape phenomenon of the piezoelectric beam. Therefore, the proposed harvester with a barrier-decreasing effect has significant superiorities in operating bandwidth and generating capability. The research findings will be beneficial to the advancement of wide-band and low-threshold nonlinear energy harvesters in the future, especially in low-frequency and low-intensity vibration environments.