Dynamic Behavior of Piezoelectric Micro 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. Another important characteristic refers to the increasing need for miniaturization of the harvesters in order to meet demands for volume in the application. In this context the so called MEMs (microelectromechanical systems) piezoelectric energy harvesters has recently gained special attention from investigators. The use of the well known cantilever piezo-beam is currently one of the most employed model in the development of micro harvesters. A difficulty in using such model is due to high values for the fundamental natural frequency (generally above 1 KHz) what makes the device useless since most of vibration signals coming from the environment rely well below that value (generally in the 0-100 Hz range). A possible solution in order to reduce the natural frequency of the fundamental mode shape of cantilever micro harvesters is to use innovative geometrical configurations that will ultimately reduce the equivalent spring constant without causing significant changes in the mass properties. This research proposal is focused on investigating novel geometrical configurations for cantilever micro harvesters in order to obtain the best possible performance in terms of the working frequency and output electrical power generation. Electromechanical models will be generated for different geometries and numerical simulations will be carried out using MATLAB. Physical prototypes will be built in order to perform experimental validation of the proposed dynamical models energy harvesters.