压电功能梯度材料中的SH表面波

为了提高声表面波器件的性能,压电功能梯度材料(FGPM)被广泛应用在声表面波(SAW)技术上,因此,压电功能梯度材料中表面波的传播特性研究变得十分重要.研究了压电功能梯度材料中SH(Shear Horizontal)波的传播特性.对于材料特性沿厚度方向为线性函数、二次函数和三次函数变化的三种形式,基于压电-弹性理论,得...     

非理想界面正交各向异性层/压电半空间结构中Love波的传播特性

研究了正交各向异性层与压电半空间非理想连接时Love波的传播特性。其中,界面条件由剪切滞后模型表征,正交各向异性层表面机械自由。首先,对压电材料和正交各向异性材料的波动方程进行求解,然后利用界面条件和边界条件推导了显函形式的频散方程,最后进行了数值计算,分析了界面性态、压电材料性能和正交各向异性程度对频散特性的影响。分析结果表明：Love波的传播速度随着界面约束强度的降低而减小;当不理想程度较高时,正交各向异性程度和压电材料性能对Love波的传播速度影响不大。     

高灵敏Love波传感器及其关键材料

Love波传感器是声表面波传感器的一种,其灵敏度最高.对Love波生物、化学传感器的研究现状进行了综述,着重分析了波导材料及其厚度、基板材料及其切向对传感器的灵敏度及温度稳定性的影响关系.指出采用高频谐振型的器件结构并结合聚合物波导的方案可进一步提高Love波传感器的灵敏度.     

表面微裂纹材料分频效应的实验研究

0引言广义声表面波是指所有在固体近表面传播的声波,因其近表面传播特性,声表面波在材料的表面和近表面性质表征方面具有独特的优势[1]。一方面,由于传播媒质的弹性参数决定了材料表面传播的声表面波特性,利用声传播媒质与周围介质的相互作用关系,发展了各类声表面波传感器[2];另一方面,声表面波脉冲对材料表面和亚表面     

波在各向异性介质中传播规律的无网格法数值模拟

采用基于紧支距离基函数近似的配点型无网格方法对波在各向异性层状介质中的传播规律进行了数值模拟,得到了应力波的传播历程,并与冲击载荷作用下的有限元计算结果值进行了比较。该方法所得到的结果与有限元计算的结果吻合较好。说明该方法可以有效地模拟波在各向异性材料中的传播过程。     

有对称液层负载时各向异性板中Lamb波的传播

1　引　言　　 L amb波是固体薄板中传播的一种弹性波 ,最初有关 Lamb波的微传感的理论研究大都只局限在各向同性板材中 ,由于在各向异性压电板上可以高效激发 L amb波 ,灵敏度高 ,体积小 ,性价比高等特点 ,因而各向异性材料有更大的实用性 ,实验上已有各向异性压电板传感器的尝试 [1] ,特别是在生物传感领域 ,由于能检测到病毒等 ,因而特别具有吸引力。在理论上 S.G.Joshi[2 ] ,Chimenti[3 ] ,Vinay Day-al[4 ] 都对各向异性板中的 L amb波进行了理论推导和数值计算 ,为了对各向异性材料微传感性的机理有进一步深入了解 ,本文研究若干…     

一种修正的GFRP本构模型及其双层板结构抗冲击特性预测

玻璃纤维增强聚合物基材料(GFRP)是一种典型的各向异性复合材料,在冲击载荷作用下具有复杂的力学响应。Autodyn软件中现有的GFRP材料模型所采用的状态方程仅考虑了体应变的单一影响,忽略了各向异性材料中应力分量与应变分量之间的耦合效应。首先,在已有的解耦理论基础上,对现有模型中的状态方程和强化模型进行了修正,计算得出了修正模型的材料参数。其次,基于弹丸剩余速度、碎片云形貌和塑性波传播三方面对比分析,验证了修正模型在计算精度和对GFRP冲击破坏机理描述等方面的优越性。最后,基于修正模型对GFRP-Al双层防护结构在不同弹丸和不同冲击速度撞击作用下的破坏模式及抗冲击特性进行了仿真计算和规律性分析。     

基于波传播方法和多元分析的正交各向异性圆柱壳振动特性研究

采用Flügge经典薄壳理论和波传播方法讨论了正交各向异性圆柱壳的自由振动问题。波传播法利用梁边界简化对应圆柱壳的边界条件,自由振动问题转换为求解关于圆频率的6次方程;通过参数化求解过程,获得了一定范围下正交各向异性圆柱壳自由振动的解空间。针对该空间应用多元统计方法讨论了圆柱壳的几何参数、材料特性参数对于频率的影响,分析了这些参数和频率的关联程度;基于方差分析讨论这些因素对频率的影响重要程度,并采用自组织映射技术研究了解空间的特性。该方法具有一般性,能够考虑正交各向异性圆柱壳在复杂边界和受外力的情况。     

柔性材料对爆炸载荷的缓冲效应研究

建立了柔性材料桙钢复合壳体在爆炸载荷作用下应力波传播问题的完备方程组;使用有限元方法完成 了对复合壳体在爆炸载荷作用下应力波传播规律的系列数值模拟,并着重讨论了不同炸药层和柔性材料层厚度 对柔性材料与钢交界面载荷的影响。     

有限长叉指换能器激发表面波及体波声场的数值模拟

采用数值方法,模拟了有限长叉指换能器(IDT)在半无限大压电晶体中激发的表面波和体波声场在晶体界面上的分布情况。在数值模拟所得结果的基础上,将频率域内的位移分量做傅立叶反变换得到时间域内声波脉冲振幅随时间的分布,并对界面上三个位移分量含有的声波模式进行分析,其中场位移分量1沿波的传播方向,位移分量2为平行于IDT指条方向,位移分量3沿基片表面法线方向。分析结果表明,界面上各位移分量中除Rayleigh波外,还含有不同比例的体波成分。其中,在位移分量1和位移分量3中占主要成分的是准纵波,在位移分量2中占主要成分的是准慢切变波。它们均按照指数方式在表面上进行传播衰减,其中准慢切变波的衰减速度小于准纵波的衰减速度。IDT指条数相对较多时的体波振幅要大于指条数相对较小时的体波振幅,且在距离IDT较近的范围内IDT指条数相对较多时体波衰减更快。     

The comparisons of thermo-elastic waves for Lord-Shulman mode and Green-Lindsay mode based on Guo��s eigen theory

The motion equations of anisotropic media, coupled to the heat conduction equations, are studied here based on the L-S model and the G-L model. The complete set of uncoupled elastic and heat wave equations for anisotropic media are deduced. The results show that the L-S model is suitable for elastic materials and the G-L model is more suitable for dissipative materials. Based on these laws, we discuss the propagation behaviors of heat wave and elastic waves for isotropic media.     

An eigen theory of electromagnetic waves based on the standard spaces

The Maxwell’s equations are studied here based on the standard spaces of the physical presentation, and the modal electromagnetic wave equations of anisotropic media are deduced. Several novel theoretical results were obtained: the number of electromagnetic waves in anisotropic media is equal to that of eigen-spaces of anisotropic media; the velocity of propagation of electromagnetic waves is dependent on the dielectric eigen-permittivity and magnetic eigen-permeability; the direction of propagation of electromagnetic waves is related on the electromagnetic eigen-operator in the corresponding eigen-space; the direction of polarization of electromagnetic waves is relevant to the eigen-electromagnetic quantities in the corresponding eigen-space. Based on these laws, we discuss the propagation behaviour of electromagnetic wave in anisotropic media.     

An eigen theory of electro-magnetic acoustic waves in magnetoelectroelastic media

The Maxwell’s equations, coupled to the mechanical equations of equilibrium, and the mechanical equations of motion, coupled to the equations of static electric and magnetic field, are studied here based on the standard spaces of the physical presentation. The complete set of uncoupled electromagnetic wave equations and elastic wave equations in magnetoelectroelastic solids is deduced. The results show that the number of electromagnetic waves and elastic waves in magnetoelectroelastic solids is determined by both the subspaces of electromagnetically anisotropic media and ones of mechanically anisotropic media. Based on these laws, we discuss the propagation behavior of electromagnetic waves and elastic waves in the transverse isotropic magnetoelectroelastic material poled in x₃.     

Transient waves in inhomogeneous anisotropic elastic shells

Summary This paper considers the problem of transient wave propagation in linearly elastic Cosserat shells of constant thickness that may be anisotropic and inhomogeneous. The methods of rays and of singular wave curves are combined to find and integrate the transport equations governing growth-decay behaviour of the six possible wave modes. Conditions on material parameters and wave geometry are obtained for various different uncouplings of the wave modes. Some special cases of propagation conditions and of decay equations are worked out in detail.     

Surface waves in fibre-reinforced anisotropic elastic media

The aim of this paper is to investigate surface waves in anisotropic fibre-reinforced solid elastic media. First, the theory of general surface waves has been derived and applied to study the particular cases of surface waves — Rayleigh, Love and Stoneley types. The wave velocity equations are found to be in agreement with the corresponding classical result when the anisotropic elastic parameters tends to zero. It is important to note that the Rayleigh type of wave velocity in the fibre-reinforced elastic medium increases to a considerable amount in comparison with the Rayleigh wave velocity in isotropic materials.     

The thermo-electromagnetic waves in piezoelectric solids

The Maxwell??s equation and stress equilibrium equation of anisotropic media, coupled to the heat conduction equation, are studied here based on the eigen theory of physical presentation, in which a new thermo-piezoelectric constitutive model is induced. The complete sets of uncoupled thermo-electromagnetic wave equations for piezoelectric solids are deduced. The results show that the equations of electromagnetic waves in anisotropic media subjected to heat become fourth order differential ones, and from them, a new phenomenon of thermo-electromagnetic waves with low propagation speed is obtained. In the final part of this paper, we discuss the propagation behavior of the new thermo-electromagnetic waves in the piezoelectric material of class 6?mm.     

Plane wave propagation and domain of influence in fractional order thermoelastic materials with three-phase-lag heat transfer

The domain of influence theorem for the fractional order theory of anisotropic thermoelastic materials with three-phase-lag heat transfer is proposed. The fractional order theory of thermoelasticity with three-phase-lag heat transfer has been used to investigate the problem. The plane wave propagation in anisotropic thermoelastic medium having a fractional order derivative in the context of three-phase-lag model of thermoelasticity is studied. The governing equations for a transversely isotropic three-phase-lag model are reduced as a special case. Some wave characteristics are computed numerically and presented graphically.     

Solitary Waves of Maxwell's Equations in Nonlinear Anisotropic Media

Abstract

The (1 + 1)-D solitary wave solutions of Maxwell's equations in nonlinearity induced anisotropic media (in liquids such as carbon disulphide, and in crystals, etc.) are investigated. We find that there is no arbitrarily linearly polarized (in the x-y plane perpendicular to the propagation direction z) soliton solution from Maxwell's equations except that with linear polarization either in alignment with or orthogonal to the geometric axis of the light induced refractive index change. This contradicts the prediction of the vector nonlinear Schroedinger equation (an approximation of Maxwell's equations) which yields soliton solutions with an arbitrary linear polarization. However, Maxwell's equations are found to admit stable elliptically polarized solitary wave solutions which reduce to the stable circularly polarized solitary wave solutions of the vector nonlinear Schroedinger equation when the induced refractive index change approaches zero.     

Scattering of a plane wave by an anisotropic ferrite-coated conducting sphere

On the basis of the three-dimensional spherical vector wave functions in ferrite anisotropic media, and the fact that the first and second spherical vector wave functions in ferrite anisotropic media satisfy the same differential equations, the electromagnetic fields in homogeneous ferrite anisotropic media can be expressed as the addition of the first and second spherical vector wave functions in ferrite anisotropic media. Applying the continue boundary condition of the tangential component of electromagnetic fields in the interface between the ferrite anisotropic medium and free space, and the tangential electric field vanishing in the interface of the conducting sphere, the expansion coefficients of electromagnetic fields in terms of spherical vector wave function in ferrite medium and the scattering fields in free space can be derived. The theoretical analysis and numerical result show that when the radius of a conducting sphere approaches zero, the present method can be reduced to that of the homogeneous ferrite anisotropic sphere. The present method can be applied to the analyses of related microwave devices, antennas and the character of radar targets.     

Transient waves in inhomogeneous anisotropic elastic plates

Summary This paper considers the problem of transient wave propagation in elastic Cosserat plates that may be anisotropic, inhomogeneous, or of variable thickness. The methods of rays and of singular wave curves are combined to find and integrate the transport equations governing growth-decay behaviour of the extensional and bending wave modes to derive a common general formula involving the material parameters and wave geometry. For inhomogeneous isotropic plates of variable thickness, conditions for the uncoupling of the wave modes are obtained and some special cases are worked out in detail.