Optimization of a Tunable Piezoelectric Harvester Applied to Multimodal Structures

The field of energy harvesting experienced a constant growth in the last years, due to the possibility of developing standing-alone wireless portable devices with extended life. In this context, piezoelectric materials appear to be particularly effective for the development of harvesters able to scavenge energy from ambient vibrations. In this paper a piezoactuated cantilever beam used for energy harvesting purposes is considered, extracting energy from a vibration source applied at the clamped boundary. The piezoelectric dimensions and position are optimized in order to maximize the coupling on the vibration modes of interest. An electric circuit containing a resistor and an inductor, connected to the piezoelectric electrodes, is optimized, for extracting the maximum electric power for any frequency of the vibration source, accounting for several vibration modes of the structure. The inductance is used to compensate the presence of a mistuning between the vibration source and the cantilever resonance frequencies. Proposed analysis shows that a single inductance is much effective when the harvester can be treated essentially as a single-degree-of-freedom structure. For harvesters with multiple degrees-of-freedom a single inductance can perform only a trade-off compensation of the mistuning between the various modes.