Theoretical Investigation On Several Problems Of Wave Propagation In Layered Magnetoelectric Composites

Magnetoelectric(ME) composites or structures consisting of piezoelectric(PE) and piezomagnetic(PM) materials are a new kind of functionally materials,which can facilitate the conversion among mechanical,electric and magnetic energies.Due to the magnetic-electric-mechanical coupling effect,ME composites are potential candidates for use as sensors,ME control components,microwave devices as well as other electric products,which makes them ready for technological application in the fields of signal processing,self-control,microwave communication and newly intelligence material systems and structures.The ME layered composites or structures consisting of alternative layered PE and PM materials are basic configurations for magnetic-electric devices.A lot of possible applications are associated with wave propagation problems in such composites.Thus,several basic problems for wave propagation in layered transversely isotropic ME composites or structures are investigated in this dissertation. The main contents are as follows.1) Reflection and refraction of plane waves at the interface between PE and PM media are studied.The reflection and refraction coefficients and energy coefficients varying with the incident angle are examined for quasi-longitudinal(QP) and quasi-transverse(QSV) waves incidence from PE or PM media.The wave mode conversion and the energy conservation and partition at the interface are discussed. The results show that the reflected and refracted wave fields consist of six different mode,i.e.the coupled QP and QSV waves,evanescent electroacoustic(EA) and magnetoacoustic(MA) waves,the uncoupled magnetic potential(MP) and electric potential(EP) waves.The most amount of the incident wave energy is carried by the waves that are of the same mode as the incident wave,while the energy arising from wave mode conversion occupies a less part of the incident energy.2) The Rayleigh-type surface wave propagation in a piezoelectric layer over a piezomagnetic half-space is investigated.The effects of four different kinds of electric-magnetic boundary conditions on the dispersion curves and mode shapes of displacements,electric and magnetic potentials are discussed.The results show that the electric boundary conditions dominate the phase velocity and mode shapes for the second mode and that the magnetic boundary conditions have a significant effect on the first mode.The larger the shear velocity of the piezoelectric layer is and the larger the phase velocity of Rayleigh-type surface wave is.3) Wave propagation along the interface in PE/PM layered periodic composites is studied.The effects of the different piezoelectric volume fraction and the properties of piezoelectric layer on the dispersion curves and the mode shapes of displacement, electric and magnetic potentials are discussed.The results show that the dispersion curves resemble the symmetric Lamb waves in a plate.Each continuous curve does not necessarily represent a single mode.Wave mode exchange takes place at the crossover point between dispersion curves of the adjoining two branches.4) Wave propagation and localization in periodic layered PE/PM structures are studied, considering two cases of wave propagation in both normal and oblique directions. Wave behaviors are analyzed by calculating the dispersion curves,localization factors and response spectra by using the transfer matrix and/or the stiffness matrix methods.The results show that the band structures are described consistently by the dispersion curves,the localization factors and the response spectra of the transmitted waves.The frequency passbands and stopbands exist in the PE/PM periodic layered structures.The width of the gaps is determined by the differences between material constants of each constituent in PE/PM composites.The bigger the difference is,the wider the gap is.The most energy is carried by the transmitted waves which are of the same mode as the incident wave when the frequencies are at the passbands.However,the transmitted coefficients of QSV or QP waves arising from wave mode conversion may be very large at some particular frequencies in some passbands.Compared to the coupled transmitted MA and EA waves,the transmitted coefficients of EP and MP waves are a little bigger.It is worth mentioning that,unlike the published works,the present dissertation has solved wave propagation problems in the layered PE/PM composites by considering magnetic potential in the PE material constitutive equations and electric potential in the PM material constitutive equations.This,we believe,not only is consistent to the actual PE/PM layered structure characteristics,but also satifies the continuity conditions accurately at the interface of the PE and PM materials from the point of view of the mathematics.Further,the new wave modes come into being physically.The investigation not only enriches the elastic wave theory of the ME composites,but also serves theoretical guide in the analysis and design of ME devices.