Simulation analysis of dynamic response of the energy harvester based on diamagnetic levitation

Based on diamagnetic levitation, the micro-vibration energy harvester is proposed, which has advantages such as low friction, low mechanical damping, low-frequency response and free of maintenance. The floating magnet is one of the most important parts in the vibration energy harvester. The dynamic properties of the floating magnet directly determine the output characteristics of the energy harvester. In order to study the vibration properties of the floating magnet, the force characteristics of the floating magnet are investigated in the vibration energy harvester. The magnetic and diamagnetic forces exerted on the floating magnet are simulated using finite element analysis software COMSOL Multiphysics. Then the dynamic characteristics of the floating magnet are further analyzed by MATLAB. In the case of the present study, when the gap between the two pyrolytic graphite plates is smaller than 7.7 mm, the floating magnet works in a monostable state. At the same time the floating magnet runs in a bistable state when the gap between the two pyrolytic graphite plates is larger than 7.7 mm. The two working states are in accordance with the experimental results. The results prove that the theoretical analysis and experimental results are in good agreement. Furthermore, the dynamic response of the energy harvester is studied in the two working states. When the coils are open-circuited and the energy harvester is in a monostable state, it is found that the dynamic response can be equivalent to that of a linear system with a nonlinear disturbance. So, the amplitude-frequency curve is right-skewed. We also analyze the influence of the gap between the two pyrolytic graphite plates on the amplitude-frequency curve. It is found that with the increase of the gap between the two pyrolytic graphite plates, the nonlinear disturbance becomes stronger, leading to a stronger right-skewed phenomenon in the amplitude-frequency curve. When the coils are open-circuited and the energy harvester is in a bistabtle state, the dynamic response is very complex, which includes double period, 4-time period and chaos. It is because the change of the amplitude of external excitation affects relative strength between the linear and nonlinear parts in the energy harvester system, resulting in the change of vibration characteristic of the floating magnet. When the coils are linked to load and the energy harvester is in a bistabtle state, the frequency of the energy harvester is consistent with that of the external excitation. This study can serve as a reference for designing the structure of the vibration energy harvester with using diamagnetic levitation. And it provides a theoretical guidance for improving the performance of the energy harvester and expanding the working bandwidth of the harvester. The energy harvester has vast application potential in wireless sensor networks and portable electronic devices.