Analytical and Experimental Investigation into Increasing Operating Bandwidth of Piezoelectric Energy Harvesters

Piezoelectric cantilevers are mostly used for vibration energy harvesting. Changing the shape of the cantilevers could affect the generated output power and voltage. In this work, vibration energy harvesting via piezoelectric resonant unimorph cantilevers is considered. Moreover, a new design to obtain more wideband piezoelectric energy harvester is suggested. This study also provides a comprehensive analysis of the output voltage relationships and deducing an essential precise rule of thumb to calculate resonance frequency in cantilever-type unimorph piezoelectric energy harvesters using the Rayleigh-Ritz method. The analytical formula is then analyzed and verified by experiment on a fabricated prototype. The analytical data was found in an agreement with the experimental results. An important finding is that among all the unimorph tapered cantilever beams with uniform thickness, the triangular cantilever, can lead to highest resonance frequency and by increasing the ratio of the trapezoidal bases, the resonance frequency decreases. It is concluded that the shape can have a significant effect on the output voltage and therefore maximum output power density. Some triangular cantilever energy harvesters can arrange in pizza form using cantilever arrays. This arrangement decreases the occupied space and can lead to increasing the power density and also operating bandwidth.