Design And Mechanism Research Of A Vehicle-mounted Piezoelectric-Electromagnetic Hybrid Wind-induced Energy Harvester

With the rapid development of in-vehicle microelectronic systems,especially the widespread application of electronic products such as sensor systems,wireless electronic devices,and low-energy microelectromechanical systems,the continuous self-supply of products has become a hot issue for domestic and foreign researchers.Traditional energy sources(such as electronic batteries,dry batteries,etc.)have limited storage power and limited lifespan,requiring regular replacement.Miniature energy harvesters are regarded as the most promising potential substitutes for traditional batteries.A large amount of wind energy is inevitably generated during driving.In this paper,a piezoelectric-electromagnetic hybrid energy harvester is designed to achieve wind energy harvesting during driving and supply energy for the in-vehicle microelectronic system.The hybrid energy harvester includes a cantilever piezoelectric wind-induced energy harvester with an airfoil and an electromagnetic energy harvester.The piezoelectric energy harvester and the electromagnetic harvester are coupled to each other through the magnetic force between the magnet at the end of the cantilever beam and the magnet at the end of the spring.The cantilever beam produces self-excited,stable amplitude vibration under the action of wind load higher than the critical wind speed,that is,flutter.At the same time,when the cantilever beam vibrates,it drives the magnet of the electromagnetic energy harvester to vibrate,thereby achieving energy capture by two mechanisms.According to Newton’s second law and Lagrangian equations,the electromechanical coupling equation of the piezoelectric cantilever beam with airfoil structure was established,and the modal function of the cantilever beam is fitted by Matlab software;according to Newton’s second law,Faraday The law and Ohm’s law the electromechanical coupling equation of the electromagnetic energy harvester was established;combine the electromechanical coupling equations of the piezoelectric energy harvester and the electromagnetic energy harvester to convert it into the vector field differential equation of the piezoelectric-electromagnetic hybrid energy harvester;a model of the repulsive force between two magnets was established by the magnetic dipole theory.A wind tunnel experiment system was set up to verify the correctness of the mathematical model of the hybrid energy harvester when subjected to wind load excitation.The experimental results show that the output voltage of the hybrid flutter piezoelectric energy harvester is higher than the output voltage of the classic flutter piezoelectric energy harvester,and it has a lower cut-in wind speed;the optimal matching load of the piezoelectric energy harvester is 160 kΩ，and the optimal matching load of the electromagnetic energy harvester is 40 Ω;the experimental results are in good agreement with the theoretical calculation results,which verifies the correctness of the mathematical model.Numerical analysis of the output characteristics of the energy harvester under wind load was carried out.The calculation results show that the piezoelectric energy has nonlinear vibration characteristics,and the higher the wind speed,the more obvious the nonlinear effect.The smaller the distance between the magnets,the larger the output voltage of the piezoelectric energy harvester and the output current of the electromagnetic energy harvester,the lower cut-in wind speed,and the lower the vibration frequency.Through the analysis of the energy harvester when subjected to the vibration of the base,the mathematical model of the energy harvester was revised,and the vibration experiment system was built to verify the correctness of the mathematical model under vibration excitation.According to the random road spectrum and the 7-degree-offreedom vibration model of the vehicle body,the vehicle body vibration excitation simulation model was established,and the energy harvesting performance was subjected to the wind load and the vehicle body vibration load at the same time.The results show that the energy harvester has no obvious cut-in wind speed when the vehicle vibration is not considered;when the vehicle speed is higher than 32 km/h,the higher the road level,the more obvious the suppression effect of the vehicle body vibration on the energy output;when the vehicle speed is lower than 32 km/h,the promoting effect of the energy output is more obvious.At the same time,the vibration of the vehicle body makes the output voltage and current waveforms more turbulent.On the E-class road,when the vehicle speed is 57 km/h,the output power of the piezoelectric energy harvester is 1.74 mW,which is 39.6%lower than the 2.88 mW on the A-class road.The output power of the electromagnetic energy harvester is 2.51 mW,which is 22.7%lower than the 3.25 mW on the A-class road.