Energy harvesting characteristics of preloaded piezoelectric beams

Abstract

A broad bandwidth is considered to be one of the most important characteristics of vibrational energy harvesters (VEHs) in order to enhance energy efficiency. To this end, an axially compressive load is applied to the VEHs of a conventional bimorph piezoelectric cantilever beam by pre-tensile cables. The theoretical framework is based on Euler-Bernoulli beam theory and the von Karman nonlinear kinetic relation, and the electromechanical coupling governing equations are derived by using the Hamilton variational principle of the total potential energy. Treatments by Galerkin discretization and the perturbation method of multi-scales give the asymptotically analytic solutions of the displacement amplitude, the voltage amplitude and the average output power, which are validated by the experimental datum in the literature. With the aid of COMSOL Multiphysics, the parametric studies are addressed to explore the mechanisms of the axial preload, the harmonic excitation, the resistance, etc, acting behind the energy harvesting characteristics. The results show that the preload does improve the bandwidth characteristic significantly, specifically, a 64% reduction in the first natural frequency and 196.6% increase of the bandwidth. The present work provides fundamental theoretical support and guides the design of potential preloaded VEHs.