Design and analysis of an exponentially tapered piezoelectric energy harvester under nonlinear rotational indirect magnetic excitation

Abstract

Piezoelectric energy harvesting from rotational motions currently receives attention as a clean and permanent energy source. However, because of low output power, optimizing and improving the efficiency of this strategy through different methods is of great importance. This study investigates a new high-efficiency piezoelectric energy harvester under rotational indirect magnetic excitation using frequency up-conversion. The studied piezoelectric energy harvester is composed of an exponentially tapered cantilever beam with a piezoelectric layer, excited magnets, a tip mass, an octagonal disk attached to the rotating shaft, and exciting magnets on the disk. The potential energy and nonlinear magnetic force are determined and substituted into an electromechanically coupled governing equation after derivation. Numerical methods are applied to solve the governing equations due to their nonlinear nature and periodic oscillations. The tip mass varies to maintain a constant natural frequency and cancel out the effect of concurrent variations of the natural frequency and tapering parameter. Verification of the theoretical model is performed by the finite element and experiment methods. The effects of some parameters, such as the tapering parameter, total resistance of the circuit, number of magnets, and rotational speed, on the output voltage and power densities are evaluated. Results show a fourfold increase in output power density when comparing exponentially tapered width to constant width. Finally, frequency response curves are plotted and analyzed to examine the effect of shaft rotational speed, subharmonics, and bandwidth. The most important result extracted from the frequency response diagram is the increase in the number of subharmonics and the observation of 2 ω/5 and 2 ω/7 subharmonic components in the frequency response of the harvester with exponentially tapered width.