Research Of Vibration Energy Harvesting Based On Piezoelectric Material

Objective of this paper is utilizing the piezoelectric effect of piezoelectric material to design a system, which can harvest energy and provide electronic equipment with this energy. Piezoelectric material is one of the electromechanical coupling materials, which can transform mechanical strain energy into electric energy and convert electrical energy into mechanical strain energy. The device which uses piezoelectric materials to transform mechanical strain energy of surroundings into electric energy is called the piezoelectric power harvesting system.The target of this paper is utilizing the strain of the piezoelectric patch to get a electric current, which will be transformed to direct current by rectification circuit. This direct current will be converted to a stable direct current by voltage booster circuit, and then a power management chip controls the process of charging up the lithium battery. The piezoelectric device can only generate a several microamperes current, which can't direct drive the circuit of chip, so that the current rectified by rectification circuit will charge up the ultracapacitor as a first step, and then this ultracapacitor will charge up the rechargeable battery. Based on the goal above-mentioned, the research is divided into following several parts:1. The piezoelectric ceramics are primary elements in piezoelectric power generation device. Based on piezoelectric theory, mechanical-electronic equivalent model and work pattern of the piezoelectric materials in vibration are analyzed, the mathematical expression of generating the power is deduced, transfer efficiency and utilization efficiency of the piezoelectric material are determined.2. Based on MATLAB software, completed is piezoelectric couple analysis of a power generation device-a cantilever beam pasted a piezoelectric patch. Harmonic input signal is applied to the cantilever beam and the beam will vibrate transversely. Output of steady state with different resistance is simulated and the relation of voltage and time is obtained under different frequencies. These results provide foundation for the experimental test.3. Test of a cantilever beam pasted a single PZT-51 patch is completed. Quantity of electric charge and voltage of the cantilever power generation device are measured under random vibration. This test is the basis of designing hardware circuit for collecting energy.4. Circuit analogue software Orcad is used to simulate the voltage equivalent circuit and design piezoelectric energy-harvesting hardware circuit. The alternating current generated from piezoelectric elements is small and unstable, so that this current needs to be rectified and filtered. The circuits designed in this paper include: voltage doubling rectifying circuit, used to transfer the alternating current from piezoelectric material to a pulsating direct current; filter circuit, rectifier circuit,used to convert the pulsating direct current to a stable direct current; DC-DC voltage booster circuit and energy collecting circuit, which are designed with Maxl678 and Maxl811, used to collect and storage the energy from piezoelectric material.Piezoelectric cantilever beam generator is designed in this paper. A continuous actuating signal is applied on the free end of the beam, and continuous alternating current is caused. The current will be rectified by the rectification circuit, and supercapacitor can buffer this energy. This is a slow cumulative process. When the voltage of supercapacitor reaches the threshold voltage 1.4V, DC voltage booster circuit and battery management circuit are turned on and energy is transported to the lithium ion battery.