Increased power output of an electromagnetic vibration energy harvester through anti-phase resonance

This paper proposes a novel method to increase the power output of a cantilever beam-based electromagnetic vibration energy harvester through anti-phase resonance. A new cantilever beam design is presented to achieve this. By introducing an anti-phase motion between the coil and the magnets at resonance under the same base excitation input, the relative velocity of the coil cutting through the magnetic field is significantly increased and hence its power output. An experiment is performed to compare the proposed method with the conventional method where either the coil or the magnet is fixed onto the vibrating base. Under a base acceleration level of 0.10 g and a natural frequency of 17.24 Hz, results shows a 185% increase in power for the proposed method when compared with the conventional method with a recorded maximum power of 7.4 mW at resonance. The power produced by this method is proven to be higher than the sum of power produced by two individual conventional harvesters under the same velocities. In addition, a 22% increase in frequency bandwidth is also recorded by the proposed method. In terms of the power density, the proposed method indicates a 38% increase when compared with the conventional harvester. Results also show a drastic reduction in the maximum power output and phase difference when the natural frequencies of the coil and the magnets differ by only 1.5%, hence defining the importance of frequency matching. Further analysis indicates that a glass fiber cantilever beam showed a higher decrease in electromagnetic damping as compared to the increase in mechanical damping when small bulk masses were added onto the beam, hence increasing its overall gain.