On The Influrence Of Piezoelectric Non-linear Electromechanical Coupling On L-beam Energy Harvesting

The electromechanical coupling of piezoelectric material is critical to the design and analysis of piezoelectric energy harvester.It has been proved that the coupling is of nonlinear,which will make the calculation more precise but more complicated as well.L-beam piezoelectric energy harvesters,which has two degrees of freedom,is taken as the as the research object.Using the method of numerical simulation,the dynamic behavior of system with piezoelectric nonlinear electromechanical coupling and its effect on the performance of the system under both simple harmonic excitation and chaos excitation of Duffing oscillator are studied,and the results are compared with the results of that with piezoelectric linear electromechanical coupling,which is regarded as a special case of nonlinear electromechanical coupling.The main research work and conclusions of this thesis are as follows:1.The lumped parameter method is used to establish the dynamic equation of L-beam piezoelectric energy harvester with piezoelectric nonlinear electromechanical coupling,and the system is divided into strong and weak magnetic force systems according to the coefficient of the first order of magnetic force.And the maximum value of absolute value of vibration displacement and mean square voltage are taken as the evaluation indicators to compare the behaviors and performance of harvester with linear and nonlinear piezoelectrice lectromechanical coupling.2.The results of simulation show that under simple harmonic excitation,there is only periodic motion in the weak magnetic force system,and there are both periodic motion and chaotic motion as well in strong magnetic force system;The variation of the piezoelectric nonlinear electromechanical coupling coefficient will lead to the changes of dynamic behavior of the system with the strong magnetic force.The internal resonance in both strong and weak magnetic force systems has the effect in frequency reduction.For weak magnetic force system,the larger the piezoelectric nonlinear electromechanical coupling coefficient,the larger the mean square voltage and the smaller the the maximum value of absolute value of vibration displacement,and for strong magnetic force system,the larger the piezoelectric nonlinear electromechanical coupling coefficient,the larger both the mean square voltage and the maximum value of absolute value of vibration displacement.Refer to the motion of the system,the difference between that with linear or with nonlinear piezoelectric electromechanical coupling is small in weak magnetic force system,but is much larger in strong magnetic force system.Refer to the performance of energy harvesting,the difference is significan only when the amplitude of excitation is larger in weak magnetic force system,and is significan forever in strong magnetic force system.3.Under chaos excitation of Duffing oscillator,results show that there is chaotic motion between wells in weak magnetic force system,and there are chaotic motions not only between wells but also in wells in strong magnetic force system.In both weak and strong magnetic force systems,the mean square voltage will increase with the increasing of the coupling coefficients.Comparing the results with the linear or nonlinear piezoelectric electromechanical coupling relationship,it is found that,as refer to the motion of system,the difference in weak magnetic force system is not obvious,but it is obvious in strong magnetic force system;and as refer to the performance,the difference is obvious in strong magnetic force system,and is also not obvious in weak magnetic force system except the case when the vibration intensity of external excitation is much higher.