Magnetic coupling and amplitude truncation based bistable energy harvester

We present a two-degree-of-freedom bistable piezoelectric energy harvester (PEH) combining both magnetic coupling and amplitude truncation mechanisms to improve the electrical response when installed within compact spaces. The PEH processes a time-varying potential well and each beam has two electrical responses due to the interaction between two magnets. The collision-induced amplitude truncation behavior leads to high-frequency vibration responses, which reduces the matching impedance of the PEH. The Hamilton's principle and the Galerkin method was applied to establish the distributed parameter model for the system. By numerical calculations, the influence of the magnet distance and beam stiffness ratio on the static potential well, as well as the influence of excitation acceleration and stop gap on the voltage and power response were explored. A series of experiments were conducted to validate the voltage and power responses under sweep and fixed frequency excitations. The experimental and simulation results agree with each other. Due to the effect of magnetic coupling, the response frequency bandwidth of the cantilever beam widens by more than 7 Hz. The frequency-up effect generated by collision increases the response power of the system with the maximum of 307.8 mW at 10^3.6 Ω in experiments, and the combination of the two widens the impedance matching range of the system. This broadband structure with a wide impedance matching range and limited motion is more suitable for practical applications.