Nonlinear analysis and power improvement of broadband low-frequency piezomagnetoelastic energy harvesters

A significant impediment to the deployment of vibration-based energy harvesting devices has been the limitation of most low-frequency transducers, usually in the form of unimorph or bimorph cantilever beam, to extract energy from a very narrow bandwidth around the transducer's fundamental frequency. In such devices, a slight deviation from the fundamental frequency causes a significant reduction in the level of harvested power by several orders of magnitudes. Additionally, most of the current research efforts on the design of piezoelectric energy harvesters have had limited success in achieving low resonance frequency. To overcome these challenges, we introduce an enhanced broadband low-frequency piezomagnetoelastic energy harvester. This harvester consists of a partially covered piezoelectric cantilever beam with a fixed magnet mass at the top of the magnet tip mass. A nonlinear distributed-parameter model based on Euler-Bernoulli beam theory and Galerkin discretization is developed. This electromechanical model is validated with previous experimental measurements for a specific value of the spacing distance between the two magnets. A parametric study is performed to determine the effects of the spacing distance between the two magnets on the static position of the harvester, natural frequency, and level of the harvested power. It is demonstrated that a decrease between the two attractive magnets results in a decrease in the natural frequency of the harvester with a strong softening behavior which gives the opportunity to harvest energy at broadband low-frequency range. The results also show that the presence and importance of the softening behavior depends on the electrical load resistance. In conclusion, the results show that depending on the available low excitation frequency, an enhanced piezoelectric energy harvester can be tuned and optimized by changing the spacing distance between the two tip magnets.