Design and experimentation of radial magnetic field vibration energy harvester based on magnetic levitation

Electromagnetic vibration energy harvesters (EVEHs) present a sustainable power solution for sensor networks in the Internet of Things. Most of the EVEHs commonly adopt the axial magnetization structure. Notably, when the magnet moves to the coil's center, the axially radiated magnetic flux lines become nearly parallel to the coil, reducing flux variation and weakening the induced current. Maintaining an effective operating area requires a significant gap between the magnet and coil, which diminishes magnetic field strength and limits device compactness. To address the problem, a radially magnetized electromechanical energy conversion unit is proposed. The magnetic flux lines radially radiated by the magnet remain highly orthogonal to the surrounding coils, increasing flux variation and enhancing electromagnetic induction. The finite element method is used to optimize the coil parameters of the radial magnetized structure, and the induced current is significantly higher than that of the axial magnetized structure. We developed a single-degree-of-freedom (SDoF-MLVEH) and a two-degree-of-freedom (TDoF-MLVEH) magnetic-levitation vibration energy harvester based on the radial magnetization structure. Two types of MLVEHs are validated using a semi-analytical approach based on harmonic balance. Simulations show that TDoF-MLVEH collects about six times more energy than SDoF-MLVEH under rail vehicle axle box excitation. Experimental results verify that the TDoF-MLVEH maintains stable output within the 0.5–1.5 g excitation range, achieving a peak power of 48.76 mW. Compared to the SDoF-MLVEH, the TDoF-MLVEH attains 66.10 % and 88.75 % higher peak power at the first and second resonant frequencies, respectively.