Propagation And Scattering Of Elastic Waves In Piezoelectric Nanomaterials And Nanostructures

Piezoelectric nanomaterials have many unique properties,such as enhanced electromechanical coupling,small scale,low power dissipation and sensitive response,etc.These advantages make them strong candidates for applications as generators,sensors,actuators,resonators and detectors in the nanoelectromechanical systems(NEMS).As one of the most important features of nanomaterials,surface/interface effects which resulted from the high ratio of surface/interface to volume commonly plays a dominant role in the overall mechanical properties of nanomaterials.Due to the presence of surface/interface effects,the bulk stress and bulk electric displacement jump across the piezoelectric surface/interface,thus the classical continuity condition is invalid.For piezoelectric nanomaterials,the surface/interface piezoelectricity and surface/interface permittivity as well as the surface/interface elasticity should be considered in predicting their electroelastic properties.In this thesis,the propagation characteristics of elastic waves in several classical piezoelectric nanostructures and nanomaterials are systematically investigated.A surface/interface is regarded as a two-dimensional continuum of zero thickness which possesses own material properties different from those of its bulk counterpart.The discontinuity of electromechanical fields at the piezoelectric surface/interface is described through the generalized Young-Laplace equations,and the influences of surface/interface elasticity,surface/interface piezoelectricity,surface/interface permittivity,surface/interface density and surface/interface residual fields are considered by using the surface/interface piezoelectricity model.The main contents are as follows:(1)The dispersion characteristics of SH guided waves propagating in piezoelectric nanoplates are studied.The dispersion relations are expressed in an explicit closed form,and the numerical examples are provided to discuss the impacts of surface material parameters on the symmetric and antisymmetric modes in details.Analysis results show that the phase velocity increases in the presence of surface elasticity and surface piezoelectricity,but it decreases with the consideration of surface permittivity and surface density.The leading factor that affects the cut-off frequency of high-order modes is surface density,and the surface elasticity,surface piezoelectricity and surface permittivity show little effect on the cut-off frequency.(2)The propagation characteristics of Lamb waves in piezoelectric nanoplates are material properties play a significant role on the angular distribution of electroelastic fields around the piezoelectric nano-cylinder.In contrast to the dynamic stress,the electric potential is more sensitive to the variation of interface piezoelectricity and interface permittivity.