Multi-modal vibration energy harvesting using the piezoelectric effect

Abstract

Over the past decade, the use of remote wireless sensing electronics has grown steadily. One main concern for the development of these kinds of devices is the power supply module. Rather than using the traditional batteries which require periodic maintenance as well as produce chemical waste, harvesting energy from the ambient environment provides a promising solution for implementing self-powered systems. Many kinds of energy sources existing in the environment can be used for energy harvesting, such as solar, wind, thermal gradient, and vibration. Among them, vibration is the most ubiquitous energy source that can be found everywhere in our daily life. There are various mechanisms to convert vibration energy into electrical energy, such as electromagnetic, electrostatic and piezoelectric transduction. Due to the property of high power density and ease of application, vibration energy harvesting using piezoelectric materials has attracted intense research interest in recent years. A conventional piezoelectric energy harvester (PEH) works as a linear resonator, whose performance greatly relies on its resonant frequency. The working bandwidth of a conventional PEH is quite narrow, while the practical vibration sources in the environment are usually frequency-variant or randomly distributed over a wide frequency range. In this thesis, a novel two-degree-of-freedom (2-DOF) PEH is developed to broaden the working bandwidth by using its first two vibration modes. This novel design can achieve wider bandwidth with two close resonant frequencies, and with no increase of the volume. Besides, such design is more compact and utilizes the material more efficiently. An experimental prototype is fabricated and tested, to investigate the behavior of this harvester. Mathematical model and FEA simulation have been developed to model this 2-DOF energy harvester. Other than using the linear multi-modal configuration, nonlinear vibration is another promising solution to broaden the bandwidth of a vibration energy harvesting system. Based on the previous linear 2-DOF PEH design, a nonlinear 2-DOF PEH is then developed by incorporating the magnetic nonlinearity. Experimental results show significant improvement of the working bandwidth as well as the powering efficiency. In the meantime, an analytical model is derived, providing good validation compared to the experiment results. Considering the real environmental vibration are always presented with varying or multiple orientations in a three-dimensional (3-D) or two-dimensional (2-D) domain, it is also important to design a harvester adaptive with different excitation orientations. A multi-modal 2-D PEH with a frame configuration is also studied in this work, which can consistently generate significant power output with excitations from any direction within a 2-D domain. Experimental study is carried out, and numerical simulation is conducted by using the combination of finite element analysis (FEA) and equivalent circuit model (ECM) methods. The results indicate its promising…