Simulation And Experimental Studies On Magnetic Nonliner Piezoelectric Energy Harvesting System Based On Fluid Induced Vibration

In recent years,to ease the energy shortage and with the development of MEMS,energy harvesting based on the positive piezoelectric effect of piezoelectric materials has attracted more and more scholars' attention.Environmental vibration energy harvesting is usually characterized by variable frequency,so widening the frequency band of piezoelectric energy harvesters is a research hotspot.Introducing magnetic force to bring nonlinearity is one of the frequency modulation methods that can be adopted.Therefore,in this paper,a set of magnetic nonlinear piezoelectric energy harvesters based on the principle of fluid-induced vibration under water is designed,whose system frequency can be adjusted through the magnetic force between the permanent magnets.Firstly,this paper establishes a mathematical model of the magnetic nonlinear energy-harvesting system,the system model parameters are divided into two parts: energy harvester structure parameters and magnetic parameters.The equivalent structural parameters of the system are solved using the principle of equivalence.The magnetic potential energy model between the magnets is established and the relationship between the introduced magnetic force parameters and the relative position of the magnet is determined.Next,the power generation performance of the system is simulated and numerical analyzed using the established mathematical model.The introduced magnetic parameters are simplified into linear stiffness coefficient 1 and nonlinear stiffness coefficient 2.The change of equivalent magnetic force parameters under different magnet position parameters are solved and the value range of the parameters needed for simulation are determined.According to the value of 1,the system is divided into hard stiffness system and soft stiffness system.Simulation results show that the hard stiffness system with negative 1 value lags the start-up flow rate and the voltage output increases at high flow rate,and this increase effect decreases with the increase of the absolute value of 2,and strengthens with the increase of the absolute value of 1.The frequency bands have been widened up to 36%,So it is suitable for applications where the flow rate is high.The soft stiffness system where 1 takes a positive value and is less than the stiffness of the vibrator itself advances the start-up flow rate,and the effect of advancement is strengthened as the absolute value of 1 increases.In the numerical simulation of the flow velocity reaching 4V,the maximum drop is 23.5%,and the fluid simulation reaches 36.4%.Voltage output generally decreases at high flow rates,but it will not decline but will increase under the appropriate parameter values.The increase in output at low flow rates greatly improves the applicable occasion of the harvester.Finally,an experimental prototype was developed based on the model of the magnetic nonlinear energy harvesting system designed in the previous article,and an experimental platform with adjustable flow rate was built to meet the experimental environment of variable-speed fluids.Then,the test experiments were conducted which show that show that the hard stiffness system lags the startup flow rate and the voltage output increases at high flow rate while the soft stiffness system advances the start-up flow rate.The drop rate of the start-up vibration velocity when the voltage reaches 4V is 33.5%,close to the rate in simulation.The improvement of the output at low flow rate is significant,at a low flow rate of 0.2m/s,the output is increased from 0.48 V to 4.9V.The results verified the correctness of the regularity of output characteristics.