The Propagation Of Rayleigh Wave In Periodically Polarized LiNbO₃ Phononic Crystals

Phononic crystal which is a new pattern of artificial functional material has great potential applications in the field of surface acoustic waves.It has received extensive attention from researchers in recent years.With the development of phononic crystal’s design and theoretical simulation,excellent phononic crystals have powerfully promoted the implementation and development of SAW devices.Due to the limited quantities and types of phononic crystals in nature,people began to explore and produce composite materials or periodic structures with different properties.Lithium niobate is a synthetic material,which has excellent physical properties such as acousto-optic,piezoelectric,etc.It can be used to design phononic crystals.Periodically poled lithium niobate formed can be achieved by an application of an electric field period domain reversed.This mode provides new ideas for phononic crystal design.In this paper,we study the propagation characteristics of Rayleigh waves in a one-dimensional structure of periodically poled lithium niobate phononic crystals.The calculation of this article provides some references for the research and design of SAW devices.Here we study the propagation of suface waves in phononic crystals which consist of piezoelectric materials.(1)We investigate the propagation of Rayleigh waves in a phononic crystal structure with a one-dimensional periodic polarized lithium niobate layer.The plane wave expansion method for deriving wave equations of Rayleigh waves in detail,the theoretically calculated results are verified by numerical simulation using the finite element method.The effects of the film thickness and filling fraction on the band gap are analyzed.The transmission of the SAW device with IDT is simulated under the different thicknesses.(2)The wave propagation in a one-dimensional piezoelectric phononic crystal with imperfect interfaces are studied,which has a metal layer on the surface.The spring model is used to describe the connection of the interface.The unit cell calculation and comparison verification are performed according to the plane wave expansion method and the finite element method.The influence of imperfect connections at the interface on the propagation of Rayleigh waves is given.Furthermore,the effect of the imperfect interface on the band gaps in the change of the thickness of the metal layer and the change of the filling fraction of the phononic crystal layer is discussed.And the influence of different imperfect interfaces on the transmission of wave propagation is considered.(3)In contrast,analyzing the influence of the initial stress on the propagation of Rayleigh waves in the periodic polarized lithium niobate layer structure.The plane wave expansion method and the finite element method are used to compare and verify the correctness of the numerical results when the initial stress along the x-axis direction is added.The effects of the film thickness and the filling fraction in phonon crystal acting on the band gaps under different initial stress conditions are discussed.