Design and experiment of piezoelectric multimodal energy harvester for low frequency vibration

Most piezoelectric vibration energy harvesters are conventional single-degree-of-freedom (SDOF) systems, and typically perform well at the single resonant mode - which makes the harvesters less efficient for low ambient vibration frequencies. In this work, we have proposed and experimentally validated a piezoelectric multimodal energy harvester having several mechanical degrees of freedom (DOFs). This multi-modal vibration energy harvester has a unique design that helps to obtain multiple resonant mode operation of the harvester at the lower frequency range. The finite element method (FEM) simulation model has been used to predict the mode shapes of the proposed energy harvester at different vibration modes. The experimental results imply that the proposed energy harvester can obtain four peak values in the range of 10-20 Hz, which are concentrated around 10, 14, 16, and 20 Hz respectively. In addition, the piezoceramic material lead zirconate titanate (PZT) has been used as a piezoelectric element that has excellent piezoelectric properties. A prototype multimodal energy harvester with four piezoelectric elements is fabricated, where a single piezoelectric element generated a peak power with a maximum of 249 pW delivered to an optimum load of 55 Ka, at 16 Hz resonant mode under 0.4 g base acceleration. In order to increase the output power and bandwidth, it is always a good idea to use multiple piezoelectric elements in one harvester structure; consequently, four piezoelectric elements of the fabricated prototype are connected in parallel. The device with parallel connected piezoelectric modules generates a peak output power of 740 W across an equivalent optimum load resistance at 3rd resonant mode (16 Hz), while the device's base is excited at 0.4 g acceleration.