Dynamic Behavior of Nonlinear Piezoelectric Energy Harvesters: Theoretical Modeling and Experimental Validation

Abstract

Increasing demand for new technologies focused on using alternative energy sources has motivated researchers from different areas to develop new procedures and techniques that ultimately can make a rational use of existing natural energy sources (wind, water, structural, etc). In this sense, the use of smart materials in the process denoted as piezoelectric energy harvesting or scavenging has considerably grown especially in the past five years. Despite the fact that the net amount of electrical energy generated by a particular piezoelectric harvester is still small, what confines its application to power small electronics, considerable progress has been verified in terms of increasing the amount of electrical energy and in improving its performance. An important characteristic of piezoelectric harvesters relies on the fact that its best performance is achieved when the device works in a resonant condition, i.e., when the frequency of the output excitation signal matches or its close enough to the harvester´s natural frequency. Small variations in the excitation frequency are enough to detune the device causing a loss in amount of electrical energy. Therefore, several researchers have focused on developing techniques that can enlarge the frequency range of operation of the device such that it becomes less sensitive to fluctuations in the spectral contents of the excitation signal. One possible alternative considers the introduction of nonlinear effects in the design and modeling of the harvester. Thus, the present research proposal aims to perform an analytical and experimental investigation in beam type piezoelectric energy harvesters with the inclusion of nonlinear effects (e.g, elastic, damping). The main goal is to evaluate real benefits in including these nonlinear effects in the design of a given harvesting device. An electromechanical model will be formulated by employing the so called cantilever beam that can be partially or fully covered by piezoelectric material in both vibrating surfaces (bimorph configuration). Numerical simulations will be performed with this model where particular types of nonlinear effects and their influence on the harvester´s output signal will be individually investigated. Experimental tests will be conducted on a prototype aiming to validate the electromechanical model formulated and to ultimately obtain a broad understanding on the physical processes that occur during the mechanical to electrical energy conversion process.