A stiffness-adjustable low-frequency electromagnetic vibration energy harvesting system with inertial amplifier

Abstract

Traditional energy harvesting devices generally suffer from poor adaptability to low-frequency environments, making it difficult for them to cope with diverse conditions. This paper proposes a stiffness-adjustable electromagnetic induction energy harvesting device comprising four sets of inclined springs connected to adjustable gears, a central vertical spring, and an inertial amplifier mechanism. By altering the rotational angle of the gears, the geometric configuration and parameters of the springs are modified, thereby regulating the system’s dynamic stiffness, natural frequency, and potential energy characteristics and enabling stiffness adjustment for different environmental vibration conditions. The electromechanically coupled dynamical equations are established, and the nonlinear restoring force is approximated using a ninth-order odd-polynomial fitting method. The harmonic balance method is employed to obtain amplitude-frequency response curves. Slowly varying harmonic coefficients are introduced to analyse the stability of periodic solutions. The fourth-order Runge-Kutta method is used to generate maps of RMS load voltage and average output power. Numerical results indicate that the proposed configuration can produce large-amplitude cross-well vibrations over low-frequency and broadband ranges. Coexisting responses and two-dimensional basin sections are computed for bistable, tristable, and quasi-zero-stiffness configurations to examine the dependence of steady-state responses on initial conditions. Finite-duration pulse excitation is used to investigate transitions among coexisting responses. Changing the pulse application time can cause the system to return to its original response, switch between potential wells, or reach a large-amplitude cross-well response. These results provide a theoretical and numerical basis for state regulation in electromagnetic energy harvesters operating under low-frequency excitation.