Propagation Properties Of Elastic Waves In Layered Piezoelectric-Piezomagnetic Nanostructures

Piezoelectric-piezomagnetic composites are a kind of new functional materials,such composites can efficiently transform the conversion among electric energy,mechanical energy and magnetic energy.The existence of multifield coupling characteristics makes them strong candidates for a wide range of applications,such as sensing,transduction,signal processing and control,etc.From the material scale,piezoelectric-piezomagnetic composites can be divided into bulk materials and nano-materials.Early studies mainly focused on the magnetoelectric bulk composites.In order to meet the requirements of miniaturization,multi-functional and integrated of magnetoelectric devices in modern high technology,magnetoelectric nanocomposites came into being.Therefore,it is significant to study the magnetoelectric properties and fundamental mechanical problems of piezoelectric-piezomagnetic nanocomposites.Based on the surface piezoelectricity theory,the elastic waves propagating in the piezoelectric-piezomagnetic nanostructures is investigated in this thesis.The main contents are as follows:The dispersion properties of SH wave propagating in a structure of piezoelectric nanofilm on a piezomagnetic half-space are investigated.The dispersion equations are given based on the two kinds of electrically boundary conditions,which are electrically shorted case and electrically open case,and numerical examples are provided to discuss the impacts of surface parameters and the thickness of piezoelectric nanofilm on the propagation properties of SH wave in detail.The results show that the phase velocity increases in the presence of surface elasticity,but it decreases with the consideration of surface density.The existence of surface piezoelectricity only increases the phase velocity significantly under the electrically open case,but has no effect under the electrical shorted case.The dispersion modes of SH wave exhibit obvious size-dependent behaviors and the surface effect may vanish when the thickness of a piezoelectric nanofilm reaches a critical value.The dispersion properties of Rayleigh wave propagating in a structure of piezoelectric nanofilm on a piezomagnetic half-space are studied.The dispersion equations are deduced according to the two electrical boundary conditions,which are electrically shorted case and electrically open case,and then numerical examples are provided to discuss the influences of surface parameters,the residual surface stress and the thickness of a piezoelectric nanofilm on the propagation properties of Rayleigh wave in detail.The results indicate that the first mode at higher frequencies may propagate in the form of dispersive Rayleigh surface waves.The phase velocity increases significantly in the presence of surface elasticity and surface piezoelectricity,but the existence of surface density reduces the phase velocity.The dispersion behaviors of the first mode show pronounced difference with the variation of residual surface stress,and the positive and negative residual surface stress induce the increase and decrease of the phase velocity respectively.For the higher-order modes,the residual surface stress has little effects on their dispersion behaviors.