Multi-degree of freedom piezoelectric energy harvesters: modeling and experimental analysis

Abstract

Endless demand for energy sources has motivated research personnel from many engineering areas to develop alternative techniques dedicated to exploit different energy sources with special attention to those coming from the environment (wind, hydraulic, motion, etc) as well as from the intrinsic operation of machines in general. In this context, the use of piezoelectric materials in the process of converting structural vibration signals into usable electric energy commonly referred in the literature to as piezoelectric energy harvesting (PEH) has been extensively studied in the past decade. It has been accepted that since the amount of harvested energy is generally small, technological applications of PEH are still restricted to powering small electronics such as sensors and sensor networks, and in this context significant progress has been achieved in developing new harvesting devices and EH methodologies. Most of reported work in this area employs the well known single degree of freedom model. The key feature of most proposed techniques is to tune the natural frequency of the energy harvesting device to the frequency of the external disturbance to maximize the energy conversion process. Several optimization techniques have been recently proposed to improve the mechanical to electrical energy conversion process as well as the tuning of the frequency of operation to the main components of the excitation frequency. An additional key feature concerning the performance of currently PEH techniques refers to the usable frequency range of the device. It has been shown that single degree of freedom harvesters present limited working range in the vicinity of the device´s natural frequency. The main goal of this project is to assess the feasibility of multi-degree of freedom dynamic models in the design of PEH. For that purpose, two degrees of freedom lumped models will be developed and the corresponding electromechanical equations in the frequency domain will be used in MATLAB® simulations in order to study the harvesting performance when multiple natural frequencies are include in the harvester model. An experimental investigation will be also conducted on a prototype specially built in order to validate some of the theoretical concepts reviewed. It is expected to gather a comprehensive understanding of the physical principles involving multi-degree of freedom PEH.