Wide Ambient Frequency Range Magnetically Coupled Piezoelectric Energy Harvester

This article presents a new magnetically coupled piezoelectric energy harvester. It is designed to harvest energy from a relatively wideband ambient vibrational source. The proposed harvester has a conventional piezoelectric cantilever with a magnetic proof mass, coupled in a magnetically repelling orientation to another U-structure, which also has a magnetic proof mass. When the source vibrates with different frequencies, both structures vibrate with different amplitudes depending on their respective resonant frequencies. However, due to the magnetic coupling, the overall output extracted from the piezoelectric cantilever is higher compared to having two independent piezoelectric cantilevers. Moreover, the magnetic coupling imparts more nonlinearity into the system, widening the frequency bandwidth where maximum energy harvesting occurs. Apart from the overall efficiency, the gain at a specific target frequency range can be improved by selecting the physical parameters of the U-structure so that its resonant frequency is driven to be within this range. Also, the resonant frequency of the piezoelectric cantilever can be tuned by altering the magnetic coupling, which indirectly changes the stiffness of the cantilever. This can be easily done by adjusting the distance between the magnets. Therefore, the proposed prototype broadens the frequency bandwidth while being very simple, economical, and requiring minimal maintenance. A theoretical study and an analytical analysis were performed on the prototype. Laboratory and field experiments demonstrated the benefits and better performance of the proposed prototype with respect to key parameters such as frequency bandwidth, total harvested power, reduction in charging time of a capacitor, and scalability.