An enhanced magnetically coupled bistable energy harvester with a spring oscillator: A numerical and experimental study

Introducing the dynamic effect of magnetic coupling to a conventional bistable energy harvester is likely to further enhance its working bandwidth and output power. In this paper, a novel two-degree-of-freedom magnetically coupled bistable energy harvester employing an auxiliary spring oscillator is proposed. The governing equations of the system are first established based on the magnetic dipole model, Euler-Bernoulli beam theory, and Lagrangian mechanics. Then the potential energy shapes, static and dynamic bifurcations, and frequency and amplitude sweeps are analyzed in detail by numerical method. Finally, a test platform is built, and swept-frequency and constant-frequency experiments are carried out. It is found that the designed harvester has complicated nonlinear dynamic characteristics, such as chaotic, superharmonic, and subharmonic responses. Compared with the conventional bistable energy harvester, its effective bandwidth is increased by at least 70%, and the excitation threshold required to trigger inter-well motion can be lowered by up to 54%. The numerical results and the experimental findings reveal that the resonance of the spring magnetic oscillator can easily induce the potential well escape phenomenon of the piezoelectric cantilever beam to run stably in high-energy orbits, resulting in an additional operating bandwidth. The presented harvester has distinguished comprehensive performance of broadband, high power, and low threshold, and is especially beneficial to harvesting energy from low-frequency and low-intensity ambient vibrations.