Bandwidth enhancement of a piezoelectric energy harvester using parametrically induced vibrations

A contemporary concept of externally coupling the vibration of a piezoelectric energy harvester with a parametrically excited beam to enhance the bandwidth of the whole system is presented in this paper. The proposed configuration not only serves in enhancing the bandwidth of operation of the harvester but also provides an option to utilize the configuration for a two directional planar vibrations case. This configuration adds a new approach to the extensive research being conducted worldwide in improving the versatility of the piezoelectric energy harvesters. The proposed configuration consists of two simple piezoelectric energy harvesters (made by attaching a macro fiber composite (MFC) patch on a substrate) with unimorph design and having tip masses with embedded cylindrical magnets. The beams are placed with the tip masses facing each other in an L-shaped configuration; when the main harvester is subject to a transverse vibration, the secondary harvester is subjected to a parametric vibration and vice versa if the directions are interchanged. The vibrating beams cause interaction between the magnetic tip masses inducing nonlinear magnetic coupling, thus modifying the linear behaviors. The magnetic tip mass of the parametrically vibrating beam induces changes in the stable equilibrium states of the whole system and also incorporates the off resonance peak due to parametrically induced resonance into the main harvester beam. In the experimental investigations aluminum and fiberglass substrates were used with varying substrate thickness and other variables like, size of the harvester, tip mass, distance between the harvester beams and base acceleration etc. were maintained constant. The whole experimental setup was subject to a frequency sweep in a range of 5-50Hz and the open circuit voltage data was obtained from the vibrating beams for both linear (no magnetic interaction) and nonlinear cases. The results obtained in this study are very promising in enhancing the bandwidth of operation of the piezoelectric energy harvesters and the concept can be extended to a case where in the vibrations from all three dimensions can be utilized in harvesting energy effectively.