A micro-electromagnetic vibration energy harvester with higher power density and wider bandwidth utilizing 3D MEMS coils

Applied Physics Letters, Volume 119, Issue 21, November 2021. In this study, the performance of an electromagnetic vibration energy harvester (EM-VEH) based on micro-electro-mechanical systems 3D coils was presented theoretically and experimentally. The VEH employs two 3D coils and E-shape iron cores inserted into the coils to reduce the magnetic leakage and to improve the output power. In this structure, the planar spring stiffness and the attraction between the iron core and magnet are nonlinear, which can broad the bandwidth. In the theoretical work, a magnetic dipole model with the integral form was derived to describe the nonlinear interaction and estimate the dynamic response, which agreed well with the finite element method results. The influence of load resistance, excitation acceleration, and initial magnet offset (IMO) was measured and analyzed experimentally. The results showed that the IMO had a significant influence on the output performance. The maximum output power of one coil can reach 57.65 μW for 250 μm IMO based on 1 g excitation with the normalized power density (NPD) of 5.08 μW/cm3 g2, along with a half power bandwidth of 4 Hz. For a smaller IMO of 174 μm, the output power reduced at 22.23 μW with the same excitation condition, while the half power bandwidth was broadened to 13 Hz. With the increase in excitation, the output power and bandwidth can be improved while the NPD reduces. The tested results proved that the structure proposed in this study can significantly enhance the output performance compared with published data.