Design Theories And Force-Electric Performances Of Broadband Piezoelectric Vibration Energy Harvester

With the development of wireless sensor network technology, the use of sustainable energy instead of chemical battery to power wireless sensor network node has become an urgent problem. That mainly due to the numerous wireless sensor network nodes that mostly work in unattended working condition for a long time, and replacing the batteries periodically and replenishing nodes energy will cause the waste of human and material resources. Therefore, seeking sustainable supply way instead of the battery-powered is key technology to break through the wireless sensor life bottleneck. Currently, piezoelectric energy harvesting technology based on environmental vibration is a new method to solve the problem. Taking advantage of piezoelectric effect of piezoelectric ceramic chip, piezoelectric energy harvester will convert vibration energy in the wireless sensor working environment into electrical energy. This technique making up defects such as the short life of battery power and environmental pollution is in the way of self-sufficient to solve its own power supply problems, and it is an new efficient, pollution-free energy harvester technology.Typically, piezoelectric vibration energy harvester is bimorph cantilever structure with a block at the tip. However, it has the general problems of single work frequency, narrow-band frequency and low energy harvest efficiency. Because environment vibration bandwidth is width and its randomness is big, the harvester and conversion efficiency of piezoelectric vibration energy harvester will be reduced greatly when the ambient vibration frequency shifts slightly off resonance frequency of piezoelectric vibration energy harvester. Therefore, how to broaden working band of the existing piezoelectric vibration energy harvester is key technology to improve its output performance.In this paper, a novel L-shaped broadband piezoelectric vibration energy harvester is presented by adding an auxiliary vertical bimorph cantilevered beam to the traditional horizontal bimorph piezoelectric cantilever structure at its free end and an L-shaped piezoelectric vibration energy harvester is composed by both coupling interactions. By changing structure dimensions and material parameters of horizontal or vertical piezoelectric bimorph cantilever to adjust the frequency spacing between the first two modes of L-shaped piezoelectric vibration energy harvester effectively, so the both modes tandem together to form a broadband work band and the goal of broadening the piezoelectric vibration energy harvester band is achieved. This structure effectively solves the problems of single work frequency, narrow-band frequency in the traditional piezoelectric bimorph horizontal cantilever.Chapter1briefly discusses the piezoelectric vibration energy harvester research significance, focusing on an overview of the piezoelectric vibration energy harvester research status at home and abroad and existing problems, and introduces advance research of broadband piezoelectric vibration energy harvester. Based on this, research thinking and research contents of paper are put forward.Chapter2mainly introduces propaedeutics of piezoelectric vibration energy harvesting technology, including the knowledge of piezoelectric theory and vibration theory, in order to provide theoretical basis for the design theories and force-electric performances of broadband piezoelectric vibration energy harvester.Chapter3mainly study structural design and finite element analysis of L-shaped broadband piezoelectric vibration energy harvester. ANSYS software is adopted to establish finite element electromechanical coupling model of L-shaped broadband piezoelectric vibration energy harvester. And the model is utilized to simulate and analyze impacts of various parameters of L-shaped broadband piezoelectric vibration energy harvester on system characteristics, such as resonance frequency, output response and so on. Furthermore, the effect of adhesive layer between piezoelectric ceramic and metal substrate is considered. So, electromechanical coupling model of L-shaped broadband piezoelectric vibration energy harvester with adhesive layer is established first. The system resonant frequency and output characteristics, which are affected by parameters, such as the thickness, density, elastic modulus of adhesive layer, are studied in detail. Finally, the optimal broadband energy harvester structure size and design parameters are determined.Chapter4studies theoretical model of L-shaped broadband piezoelectric vibration energy harvester. According to piezoelectric theory, Euler-Bernoulli beam vibration theory and Hamilton’s principle, electromechanical coupling mathematical model of L-shaped broadband piezoelectric vibration energy harvester under the clamp-free boundary conditions is first established to obtain the system resonant frequency and the characteristic equation. Then, the influences of various parameters of L-shaped broadband piezoelectric vibration energy harvester on system modal frequencies, terminal velocity, output voltage, output current and output power are analyzed through MATLAB software to obtain main factors of vibration frequency, energy output characteristics of L-shaped broadband piezoelectric vibration energy harvester.Chapter5studies and establishes the equivalent circuit model of L-shaped broadband piezoelectric vibration energy harvester. Crossing structure design and circuit design, the piezoelectric element of L-shaped broadband piezoelectric vibration energy harvester is equivalent to constant current source connected in series. So, the equivalent circuit model is first obtained between L-shaped piezoelectric vibration energy harvester and load impedance. Power optimization and load optimal design are adopted to the output characteristic of L-shaped broadband piezoelectric vibration energy harvester by using this model so that the best match load impedance and the maximum output power are gained in the first and second mode excitation of system. Finally, the optimal load impedance of L-shaped broadband piezoelectric vibration energy harvester in the short-circuit resonance and open-circuit resonance conditions are obtained through the comparative analysis of the simulation data analysis.