Finite element modeling and characterization of a magnetoelastic broadband energy harvester

Piezoelectric-based vibration energy harvesters have been extensively developed to the end of replacing low-power batteries. However, matching the frequency of the ambient vibration is not always possible and to broaden the frequency response of the harvesters, different proof-of-concept devices have been developed. This work presents a miniaturized device intended for magnetoelastic broadband vibration energy harvesting. The device consists of a silicon beam where ferromagnetic foils act as proof mass and interacts with an external pair of permanent magnets. The interaction is first simulated using a Finite Element Method (FEM) model for different distances between the magnets and beam (a) and between the magnets (b). This is done for both an attractive and a repulsive magnet configuration and the calculation is performed for a set of a and b values. Both spring softening and hardening effects are observed for the two magnet configurations. The attractive configuration has a monostable potential energy landscape with an associated spring softening for a large range of a and b values which makes this configuration very useful for energy harvesting applications. The attractive configuration is experimentally investigated by impedance measurements. These measurements are performed for a ∈ [400 μm, 2500 μm] and b ∈ [320 μm, 3140 μm] and a region that allows for broadband harvesting is found experimentally. Compared to the linear case the largest spring softening effect yielded a decrease in the effective spring constant of 74%, a decrease in the resonant frequency of 49%, and the coupling coefficient was increased with a factor of 2.6.