Propagation Of Surface Waves In Layered Media Of Cubic Piezoelectric Crystal With Imperfect Interface

Piezoelectric materials are widely used to make resonators,sensors,transducers,tunable filters and other electron devices due to being able to achieve the conversion between mechanical energy and electrical energy.In order to achieve high performance,in many cases,surface acoustic wave devices often adopt a layered structure where a thin or thick piezoelectric layer is deposited on an elastic substrate or reverse structure.The elastic wave theory is one of the most important fundamental for the analysis and design of acoustic wave devices.In practice,due to the factors such as mismatching of material properties,microcracks,holes,degumming,and adhesion aging,etc.,the layer structure often has some defects,and these defects will have important effects on the performance of the piezoelectric devices.Therefore,the studies of elastic waves propagating in piezoelectric layered system with interfacial imperfections have important theoretical significance and application value.Meanwhile,due to the fact that the macroscopic symmetry and material matrixes of piezoelectric cubic crystal are in conformity with the piezoelectric semiconductor,the understand of the wave propagation in piezoelectric cubic crystals can provide some references for the design and optimization of acoustic amplification and charge transmission devices of piezoelectric semiconductor.Propagation characteristics of Love waves in piezoelectric layered systems consisting of a piezoelectric cubic crystal layer and a dielectric substrate is firstly investigated.Based on the spring-type relation,the mechanical and electrical imperfections of the interface between the piezoelectric layer and the substrate are dealt with,and the exact dispersion equations are obtained for electrically open and shorted circuits by taking the cut orientations of the piezoelectric cubic crystal into account.It is shown that the bulk shear wave velocity,the BG wave velocity and the limiting wave velocity for different cut angles are symmetric with respect to 45~°and can obtain the maximum velocities at the angle of 45~°.The mechanical imperfection of the interface can significantly reduce the phase velocity of Love waves,while the electrical imperfection has nearly no effect on the dispersion curves.Subsequently,the propagation behaviors of Rayleigh-type surface waves in an analogous piezoelectric configuration are studied under the considerations of both perfect bonding and imperfect bonding.The effects of the electrical boundary condition,the property of piezoelectric materials as well as the interface bonding on the phase velocity,the electromechanical coupling factor and the modes are analyzed in detail.The numerical results show that the velocity of Rayleigh wave for electrically open case is slight larger than that of electrically shorted circuit.The property of piezoelectric materials plays a dominant role in the dispersion relation,and the electromechanical coupling can be achieved a strongest performance when the cut angle is equal to 45~°.The mechanical imperfection has great effects on the dispersion curve in the range of relative small wavenumbers and gradually disappears with the increasing of wavenumber.Comparing with the electrical imperfection the effects of mechanically imperfect bonding are more significant.The displacements and electric potential in the elastic substrate can rapidly decay away from the interface as the deep increasing which implies that the energy carried by surface waves should be trapped in the piezoelectric layer.The obtained results can offer a theoretical basis for the optimal design of piezoelectric acoustic wave devices.