Frequency tuning design for vibration-driven electromagnetic energy harvester

The common resonant-based vibration energy harvester effectively converts mechanical vibration to electrical power when an ambient excitation frequency matches the specific resonant frequency of the device. The resonant frequencies of energy harvesters are generally fixed during the design process and cannot be changed after fabrication. Therefore frequency tuning technology that allows for operation in a wide frequency range is desirable for a vibration energy harvester. In this study, the authors proposed a novel frequency tuning design of vibration-driven energy harvester, which used electromagnetic conversion. The proposed frequency tuning method uses a rotatable spring in order to adjust the spring constant. Through this tuning method, the resonant frequency of the harvester can be manipulated simply by rotating the spring. The proposed tuning-based energy harvester has been successfully tuned to have a resonant frequency from 23 to 32 Hz. These test results agree with the ANSYS analysis presented. The experimental results demonstrated that the proposed energy harvester can generate a maximum power output of 60 μW with an acceleration of 0.5 g (1 g = 9.81 m/s²). When the proposed harvester was attached to an automobile engine, a maximum open-circuit voltage of 1.78 V_pp was produced at 700 RPM.