Design of a nonlinear energy harvester based on high static low dynamic stiffness for low frequency random vibrations

Most of the vibration sources, which could be used for energy harvesting, are vertical and very low frequency (e.g. human movement, vehicle transportation, etc…). Under those conditions and while considering the size constraints, usual vibration energy harvesters (VEHs) underperform due to the combined effect of gravity, mechanical damping and the necessity to be tuned to very low frequencies. In order to overcome these limitations, the concept of High Static Low Dynamic (HSLD) stiffness is proposed and validated for VEHs. To do so, a theoretical study is performed to optimize the electromagnetic structure and design a folded-beam suspension of the moving mass allowing a low mechanical damping. This leads to the design of an original VEH, which is experimentally characterized under harmonic and white noise excitations. Compared to the literature, it demonstrated high performances with up to 41.3 mWcm−3 g−2 of normalized harvested power at an operating low frequency of 5.3 Hz.