Preliminary Study of Optimum Piezoelectric Cross-Ply Composites for Energy Harvesting

Energy harvesting devices based on a piezoelectric material attached to asymmetric bistable laminate plates have been shown to exhibit high levels of power extraction over a wide range of frequencies. This paper optimizes for the design of bistable composites combined with piezoelectrics for energy harvesting applications. The electrical energy generated during state-change, or “snap-through,” is maximized through variation in ply thicknesses and rectangular laminate edge lengths. The design is constrained by a bistability constraint and limits on both the magnitude of deflection and the force required for the reversible actuation. Optimum solutions are obtained for differing numbers of plies and the numerical investigation results are discussed. 1. Introduction Energy harvesting which converts ambient mechanical vibrations into electrical energy is an area of considerable research interest and has received extensive attention in the past decade. A variety of methods have been considered including inductive, capacitive, and piezoelectric materials [1–3]. In many cases harvesting devices have been designed to operate at resonance to optimize the power generation, for example, simple linear cantilever beam configurations. However, ambient vibrations generally exhibit multiple time-dependent frequencies which can include components at relatively low frequencies. This can make typical linear systems inefficient or unsuitable; particularly if the resonant frequency of the device is higher than the frequency range of the vibrations it is attempting to harvest. In order to improve the efficiency of vibrational energy harvesters, recent work has focused on exploiting nonlinearity for broadband energy harvesting. Encouraging results [2] have been obtained using nonlinear or bistable cantilevered beams. Stanton et al. [2] modeled and experimentally validated a non-linear energy harvester using a piezoelectric cantilever. An end magnet on the oscillating cantilever interacts with oppositely poled stationary magnets, which induces softening or hardening into the system and allows the resonance frequency to be tuned. This technique was shown to outperform linear systems when excited by varying frequencies. However, such a system would require an obtrusive arrangement of external magnets and could generate unwanted electromagnetic fields. An alternative method has been recently found where a piezoelectric element is attached to bistable laminate plates with 2 plies and a total ( ) layup of to induce large amplitude oscillations [3]. Such harvesting structures have