In recent years, several strategies have been proposed to improve the functionality of energy harvesters under broadband vibrations, but they only improve the efficiency of energy harvesting under limited conditions. In this work, a comprehensive experimental study is conducted to investigate the use of magnets for improving the functionality of energy harvesters under various vibration scenarios. First, the nonlinearities introduced by magnets are exploited to improve the performance of vibration energy harvesting. Both monostable and bistable configurations are investigated under sinusoidal and random vibrations with various excitation levels. The optimal nonlinear configuration (in terms of distance between magnets) is determined to be near the monostable-to-bistable transition region. Results show that both monostable and bistable nonlinear configurations can significantly outperform the linear harvester near this transition region. Second, for ultra-low-frequency vibration scenarios such as wave heave motions, a frequency up-conversion mechanism using magnets is proposed. By parametric study, the repulsive configuration of magnets is found preferable in the frequency up-conversion technique, which is efficient and insensitive to various wave conditions when the magnets are placed sufficiently close. These findings could serve as useful design guidelines when nonlinearity or frequency up-conversion techniques are employed to improve the functionality of vibration energy harvesters.
A multi-source micro power generator employing thermal and vibration energy harvesting
