A variable stiffness oscillator for vibration energy harvesting

Abstract

One of the most significant issues for resonance-type vibration energy harvesters is their narrow operation bandwidth. In order to provide them an ability to tune themselves to the frequency variation, a variable stiffness cantilever oscillator that uses an electro permanent magnet (EPM) to change its effective length is proposed in this study. , The EPM, which consists of two different kinds of permanent magnets with different levels of coercivity, connected by iron yokes, and a magnetization coil, can turn its holding force on and off by reversing the magnetization of the magnet by activating the magnetization coil with a current pulse. Thus, by placing the EPM in the middle of a cantilever, a tunable oscillator can be realized which can change its natural frequency low to high. It is also described that there are two statuses of the activated EPM, i.e., fully activated (FA) and partially activated (PA), and the holding force of the latter can be much weaker than that of the former. Frequency sweep excitation tests are conducted to show that the oscillator shifts its resonance peak to the higher frequency when the EPM is fully activated, but does not exhibit any distinct resonance when the EPM is partially activated.