Electromechanical behavior of a pendulum-based piezoelectric frequency up-converting energy harvester

In the present study, the possibility to extract more vibrational energy by utilizing a high number of magnets on the proof mass of a piezoelectric frequency up-converting energy harvester is investigated. Due to magnetic interaction, the beam is actuated whenever the proof mass passes over its tip. It is observed that several peaks occur in the voltage signal of PZT beam when the angular velocity of the proof mass increases linearly. It is shown that the peaks locations which found to be dependent on the natural frequency of the PZT beam as well as the number of rotating magnets can be estimated by a mathematical formulation. Considering the effects of magnetic interactions on the pendulum dynamics, the generated power of the harvester is obtained for harmonic excitations. Although the determination of exact optimum number of magnets that can lead to the best generated power in all excitation characteristics is impossible, it is found that by applying an appropriate number of rotating magnets (e.g. six, seven or eight magnets), the extracted power from high amplitude excitations can be enhanced. It is noteworthy that, at some particular cases, it is possible that the generated power be increased to even more than ten times. At the end, by conducting some experiments, the validity of the mathematical modeling as well as the applied numerical method is examined.