有限入射声束在液固界面声反射的数值研究

采用将有限声束分解为一系列平面波的方法，对液固界面声束的声反射问题进行了数值研究，结果表明，当声束入射角为瑞利疲激角时，反射声速有明显位移；当声束在液固界面“掠射”时，反射声速显著变宽，文中还讨论了束宽对反射声速横截面上声场分布的影响。     

固-固界面退化特性的超声反射评价方法

提出了一种基于有限宽超声束反射的固-固界面退化特性评价方法,从理论和数值仿真角度进行了分析和计算。将两固体界面间的薄层简化为界面弹簧模型,以界面法向和切向劲度系数表征界面的退化程度。通过数值计算求得有限宽超声纵波束在不同入射角和界面不同退化程度下的反射横波、反射纵波的镜面反射系数。进一步地,通过建立二维有限元模型,仿真研究了有限宽超声纵波束在给定入射角及界面不同退化程度下镜面反射系数的变化规律。结果表明,反射纵波和反射横波的镜面反射系数随有限宽超声纵波束的入射角及界面劲度系数的改变而变化,且存在镜面反射系数随界面劲度系数单调且敏感变化的入射角,据此可准确评价界面的退化程度。     

正交各向异性板液/固界面的声反射与声透射

采用Legendre正交多项式法,对液/固界面声波反射和透射系数进行求解。利用Legendre正交多项式对正交各向异性板中的位移解进行展开,推导出板中的应力和波动控制方程。联立液/固界面的边界条件和波动控制方程,建立线性无关方程组,用以计算液/固界面的反射和透射系数及Legendre多项式的展开系数,计算所得铝板液/固界面的反射和透射系数与传递矩阵法的计算结果吻合良好。以单向纤维增强复合材料板为例,在不同的方位角下,分析了反射和透射系数随斜入射角度、入射波频率的变化关系,以及板中声场的位移分布。所取Legendre正交多项式截止阶数越大,可用来计算的频厚积范围越大。研究拓展了Legendre正交多项式法的适用范围,为材料力学性能的声学测量提供了理论基础。      

有流存在时三层流体界面波的二阶Stokes波解

以小振幅波理论为基础，利用摄动方法研究了有背景流场存在时密度三层成层状态下的界面内波，得到了各层流体速度势的二阶渐近解及界面内波波面位移的二阶Stokes波解，并讨论了界面波的Kelvin-Helmholtz不稳定性.结果表明：有流存在的情况下三层密度成层流体界面内波的一阶渐近解(线性波解)、频散关系及二阶渐近解不仅依赖于各层流体的厚度和密度，也依赖于各层流体的背景流场；界面内波波面位移的二阶Stokes波解不仅描述了界面波之间的二阶非线性相互作用，也描述了背景流与界面波之间的二阶非线性相互作用；当每层流 关键词： 界面波 均匀流 二阶Stokes波解 Kelvin-Helmholtz不稳定性     

非线性左右手媒质界面的Goos-Hänchen位移

 由均匀平面电磁波在左右手媒质界面满足的切向边界条件出发,推导了电磁波由线性传统媒质入射到非线性左手媒质时波的传播特性。利用时间延迟的方法,给出全反射情况下媒质界面非线性Goos-Hänchen位移表达式。分析了非线性左手媒质界面的侧向位移随入射角及入射波电场强度的变化关系,发现入射波场强对传输特性起决定作用:当入射波电场小于临界场强时,调节入射场强可以控制相应的侧向位移;当入射波电场大于临界场强时,不再满足全反射条件,部分入射波透射到非线性介质中。波导中加入非线性介质不仅可以调节侧向位移的大小,且可以实现对入射波场强的控制。     

非线性左右手媒质界面的Goos-H(a)nchen位移

由均匀平面电磁波在左右手媒质界面满足的切向边界条件出发,推导了电磁波由线性传统媒质入射到非线性左手媒质时波的传播特性.利用时间延迟的方法,给出全反射情况下媒质界面非线性Goos-Hǎnchen位移表达式.分析了非线性左手媒质界面的侧向位移随入射角及入射波电场强度的变化关系,发现入射波场强对传输特性起决定作用:当入射波电场小于临界场强时,调节入射场强可以控制相应的侧向位移;当入射波电场大于临界场强时,不再满足全反射条件,部分入射波透射到非线性介质中.波导中加入非线性介质不仅可以调节侧向位移的大小,且可以实现对入射波场强的控制.     

线偏振光在手征负折射介质中的古斯汉欣位移特性研究

从理论上分析了手征负折射介质中的横向位移特性,给出了线极化波入射条件下发生全反射时的横向位移随入射角的关系曲线。当入射角处于两个本征波的临界角之间时,TE和TM分量对应的横向位移方向相反。而当入射角大于全内反射角时,两个分量都将朝着正方向发生横向位移。通过比较发现手征负折射介质中的古斯汉欣位移特性与常规介质和一般手征介质也有着很大的不同之处。     

各向同性固体界面非线性反射的实验研究

实验测量了SV波入射到玻璃-空气,玻璃-铁、铜、铝界面上时反射的二次谐波SV波,研究了非线性反射效率与入射角以及材料的线性和非线性特性的关系,发现在某些入射角下,反射的二次谐波会有较大的振幅,报道了实验结果并和理论进行了比较。     

电介质膜对受抑全内反射结构中古斯-汉欣位移的增强

受抑全反射结构中,反射光束和透射光束的古斯汉欣(Goos-Hanchen)位移同时存在,对称双棱镜结构的受抑全反射古斯汉欣位移通常只有波长量级,在实验中很难测量。计算了在入射角大于棱镜与空气界面的临界角小于棱镜与薄膜界面临界角时,镀有电介质膜的对称双棱镜的受抑全反射过程中入射光束的反射系数和透射系数的复数表达式。利用稳态相位法计算得出透射光束和全反射光束的古斯汉欣位移。结果表明,反射光束和透射光束古斯汉欣位移量相同,与入射角大小、薄膜厚度以及空气层厚度有关。在入射角小于但接近棱镜与薄膜界面的临界角,薄膜厚度和空气层厚度一定时,古斯汉欣位移量共振增强达到波长的数百倍。     

考虑非傅立叶效应的固液相变分子动力学模拟

采用耦合双温度模型的分子动力学方法对飞秒激光照射金箔的固液相变过程进行了模拟研究,利用序参数法对固液原子进行判定从而确定了金箔发生相变时的固液界面位置和温度,对基于傅立叶定律的抛物线模型和考虑非傅立叶效应的双曲线模型模拟得到的结果进行对比分析,在此基础上采用耦合双曲线模型的分子动力学方法研究了激光能量密度和脉冲宽度对金箔相变过程的影响.结果表明,当激光作用于金箔时,金箔上表面首先熔化,固液界面随时间不断向金箔底部移动,并且在相同条件下,双曲线模型下的金箔熔化深度和固液界面温度均大于抛物线模型的结果.当考虑非傅里叶效应时,激光能量密度越大,固液界面温度越高,金箔熔化时间越短;激光脉冲宽度越小,固液界面温度越大,金箔熔化速度越快.     

Scattering of SH wave by a semi-cylindrical salient near vertical interface in the bi-material half space

With the aid of the Green function method and image method, the problem of scattering of SH-wave by a semi-cylindrical salient near vertical interface in bi-material half-space is considered to obtain its steady state response. Firstly, by the means of the image method, Green function which is the essential solution of displacement field is constructed to satisfy the stress-free condition on the horizontal boundary in a right-angle space including a semi-cylindrical salient and bearing a harmonic out-of-plane line source force at any point on the vertical boundary. Secondly, the bi-material is separated into two parts along the vertical interface, then unknown anti-plane forces are applied on the vertical interface, and according to the continuity condition, the first kind of Fredholm integral equations is established to determine unknown anti-plane forces by “the conjunction method”, then the integral equations are reduced to the linear algebraic equations by effective truncation. Finally, the dynamic stress concentration factor (DSCF) around the edge of semi-cylindrical salient is calculated, and the influences of incident wave number, incident angle, effect of interface and different combination of material parameters, etc. on DSCF are discussed.     

Lateral displacement of a Gaussian beam reflected from absorbing media

Lateral displacements of well-focused beams reflected from absorbing media are demonstrated in this paper. The incident beam is modeled as a tapered wave with a Gaussian spectrum. The field solutions are obtained on both sides of the interface by solving analytically from Maxwell's equations and by matching the boundary conditions at the interface. Numerical simulations are presented and the field values as well as the time-averaged power densities are computed. The influences of the polarization, the angle of incidence and the beam width on the displacement are discussed. The origin of the displacement lies in the absorption of the media, for which there is a phase shift between the incident and reflected waves. Because of this phase shift, the center of the reflected beam does not coincide with that of the incident one, similar to the Goos-Hänchen shift.     

负介电常数材料与负磁导率材料双层结构的透射特性

利用麦克斯韦方程组研究了负介电常数材料和负磁导率材料组成的双层结构的透射特性.电磁波在跨越负介电常数材料层和负磁导率材料层的界面时，由边界条件导致了电磁场的大部分能量局域在界面上，形成特殊的界面模式.研究结果表明，当入射角满足某个特定条件时，这些界面模可以演变为共振隧穿模，导致共振透射的发生.这种输运特性可以实现带通滤波. 关键词： 负介电常数材料 负磁导率材料 单负材料 带通滤波器     

Acoustic scattering by a modified Werner method

A modified integral Werner method is used to calculate pressure scattered by an axisymmetric body immersed in a perfect and compressible fluid subject to a harmonic acoustic field. This integral representation is built as the sum of a potential of a simple layer and a potential of volume. It is equivalent to the exterior Helmholtz problem with Neumann boundary condition for all real wave numbers of the incident acoustic field. For elastic structure scattering problems, the modified Werner method is coupled with an elastodynamic integral formulation in order to account for the elastic contribution of the displacement field at the fluid/structure interface. The resulting system of integral equations is solved by the collocation method with a quadratic interpolation. The introduction of a weighting factor in the modified Werner method decreases the number of volume elements necessary for a good convergence of results. This approach becomes very competitive when it is compared with other integral methods that are valid for all wave numbers. A numerical comparison with an experiment on a tungsten carbide end-capped cylinder allows a glimpse of the interesting possibilities for using the coupling of the modified Werner method and the integral elastodynamic equation used in this research.     

Harmonic generation of an obliquely incident ultrasonic wave in solid-solid contact interfaces

The conventional acoustic nonlinear technique to evaluate the contact acoustic nonlinearity (CAN) at solid-solid contact interfaces (e.g., closed cracks), which uses the through-transmission of normally incident bulk waves, is limited in that access to both the inner and outer surfaces of structures for attaching pulsing and receiving transducers is difficult. The angle beam incidence and reflection technique, where both the pulsing and receiving transducers are located on the same side of the target, may allow the above problem to be overcome. However, in the angle incidence technique, mode-conversion at the contact interfaces as well as the normal and tangential interface stiffness should be taken into account. Based on the linear and nonlinear contact stiffness, we propose a theoretical model for the reflection of an ultrasonic wave angularly incident on contact interfaces. In addition, the magnitude of the CAN-induced second harmonic wave in the reflected ultrasonic wave is predicted. Experimental results obtained for the contact interfaces of A16061-T6 alloy specimens at various loading pressures showed good agreement with theoretical predictions. Such agreement proves the validity of the suggested oblique incidence model.     

锗薄膜透射光学二次谐波研究

本文采用固定入射角，改变入射光偏振方位角的方法从实验上了研究了锗薄膜的透射光学二次谐波产生及其变化规律，并从理论上推导了产生透射二次谐波的表达式，最后拟合求得描述面谐波电流的唯象参数ａ。     

Coupling of Acoustical Plane p-Wave to a Cased Borehole

Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot＇s theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.     

Dynamic stress around a cylindrical nano-inhomogeneity with an interface in a half-plane under anti-plane shear waves

Taking into account the size of the nanostructure, the effect of surface/interface stiffness on the dynamic stress around a cylindrical nano-inhomogeneity embedded in an elastic half-plane subjected to anti-plane shear waves is investigated. The boundary condition at the straight edge of the half-plane is traction free, which is satisfied by the image method. The analytical solutions of displacement fields are expressed by employing a wave function expansion method. The addition theorem for a cylindrical wave function is applied to accomplish the superposition of wave fields in the two half-planes. Analyses show that the effect of the interface properties on the dynamic stress is significantly related to the nano-scale distance between the straight edge and the center of the cylindrical nano-inhomogeneity. The frequency and incident angle of incident waves and the shear modulus ratio of the nano-inhomogeneity to matrix also show different effect on the dynamic stress distribution when the inhomogeneity shrinks to nano-scale. Comparison with the existing results is also given.     

Fringed sound fields and their interaction with liquid-solid interfaces

On the one hand, it is well known that Gaussian beams possess the ability to stimulate Rayleigh waves, resulting in the Schoch effect, a lateral beam displacement. This effect, often characterized by a reflected sound pattern consisting of two anti-phase beams, is due to the re-radiation of sound because of the stimulation of leaky Rayleigh waves. On the other hand, fringed sound beams are characterized by the fact that they consist of a number of neighboring anti-phase narrow beams. They are a first approximation of a sound field originating from a phased array of harmonic vibrating crystals in which each crystal vibrates in anti-phase compared to its neighbor. The individual lobes within the fringed sound pattern diverge much less than standard Gaussian beams of the same size. The current study investigates the interaction of fringed beams with a liquid-solid interface. It is found that under certain conditions, a fringed beam, incident at the Rayleigh angle, produces a reflected sound pattern that contains a wide lobe that is not fringed. It is also shown that under other conditions, contrary to the famous forward displacement of the reflected sound for incident Gaussian beams, a strong backward displacement occurs for fringed beams.