Study On Theory And Method Of High-frequency Vibration Excitation And Sensing Based On Flexoelectricity

Flexoelectricity—a electromechanical coupling between strain gradient and polarization.The unique effect shows a significant size effect,which increases with the reduction of material size.In recent years,actuators and sensors based on the flexoelectric effect have attracted much attention,but researchers focus on the flexoelectric response at low frequency or quasi-static state(< 10Hz),and few articles interest performance of flexoelectric materials at high frequency.The purpose of this paper is to study the response of flexoelectric actuator beam and sensing beam at high frequency.The static bulk flexoelectric effect is customarily described by the expansion of the thermodynamic potential(density).Integrating the free energy density with components of strain tensor over the plate thickness,one finds the constitutive equations.A pin-force-moment model is proposed to predict and verify the coupling between actuator and substrate.Based on the shear and normal stress between the actuator and the substrate,the analytical solution of Lamb wave propagation in the substrate excited by actuator is derived.Furthermore,according to the distribution characteristics of shear and normal stress,the closed solution of Lamb wave propagation is obtained,and the modal modulation of Lamb wave is realized by the modulation function.Lamb wave modulation under the excitation of actuator was successfully realized by finite element simulation,which verified the effectiveness of flexoelectric beam.A piezoelectric-flexoelectric beam bimorph structure is designed.Based on the dynamic response of flexoelectric beam under high frequency excitation,the residual piezoelectricity,surface piezoelectricity and flexoelectric response of beam in bimorph structure are analyzed and calculated.Furthermore,the effective flexoelectric coefficient is calculated,which is consistent with the flexoelectric coefficient reported in the review.It is proved that there is a flexoelectric response in the piezoelectricflexoelectric beam,and the validity of the flexoelectric sensing beam model is verified.In this work,the analysis reported here could provide the guideline for designing structural health monitoring system based upon flexoelectric actuators,and also verify the feasibility of flexoelectric beam as high-frequency sensor.