柱状固体复合结构对斜入射超声波的散射

较详细阐述了三层柱状固体复合结构对斜入射超声波的散射理论．厚度远小于声波波长和内层半径的中间圆环可模拟为内外层媒质之间的界面薄层．将声波斜入射时中间国环层力学量的传递矩阵作线性近似展开，我们首次建立了描述界面薄层的三维弹簧物理模型，由此进一步分析了固体界面处的声学边界条件．利用弹簧模型，我们最后从数值上研究了玻璃纤维／铝基复合结构中界面薄层力学参量的变化对斜入射超声散射截面积的影响．     

横向各向同性柱状复合结构对超声波的散射

首先描述了横向各向同性复合圆柱结构的入射声场、散射声场及内部的驻波声场，然后利用转移矩阵方法导出了求解散射声场的方程组，计算了铝／各向异性界面层／纤维复合结构对斜入射声波的背向散射谱和散射截面积。将柱状复合结构中各向异性界面薄层相应的转移矩阵作渐近展开，建立了模拟这种界面薄层的弹簧模型及界面处广义边界条件。结果表明，模型中劲度常数仅依赖于界面薄层厚度及界面层媒质的弹性常数Ｃｌｌ，Ｃ１２和Ｃ４４，而振子质量与Ｃｌｌ，Ｃ４４，Ｃ１３和Ｃ３３有关。     

固体间界面的物理模型和界面对声波的反射

简要描述了模拟两固体间界面特性的弹簧模型，该模型最早是根据静力学方法提出的，后来用固体间界面薄层的声波反射方法加以改进，从界面弹簧模型可以方便地得到界面外近似边界条件，其中包含界面“弹簧”振子的劲度常数和质量，文章还给出了两相间固体中界面声反射系数的表达式，介绍了测量界面劲度常数的超声反射谱方法。最后讨论了仍关声波与界面相互作用研究领域中最近的一些研究进展。     

平面声波斜入射到水中无限长圆柱壳体的纯弹性共振散射

斜入射情况下水中弹性圆柱壳体的共振声散射问题至今还很少被研究。本文导出了平面声波斜入射时水中无限长圆柱壳体纯弹性共振散射函数的简单而明显的表达式。针对中空铝圆柱壳体（ｂ／ａ＝０．８）详细计算了不同入射角时纯弹性共振散射的分波共振谱，同时还给出了远场反向散射形态函数及其刚硬背景隔离，发现形态函数受吻合频率的影响很大。文中详细计算了斜入射时无固次复频率平面上的共振复极点分布，并由此计算了不同入射角时各阶共振模式，特别是附加共振模式所对应螺旋环绕波的相速度频散曲线。这些结果十分有助于认识声波斜入射下圆柱壳体的共振和再辐射的物理本质。     

各向同性媒质中球体声散射的共振模式缺损

以有机玻璃中铁球的共振散射为例，研究了各向同性媒质中球状散射体的共振模式缺损问题 . 通过对纵波和横波散射系数的数值分析，指出在纵波入射时的散射纵波（简称p→p散射） 中零阶分波会出现共振模式缺损，导致共振模式缺损的数值原因是纵波散射系数分式中分子 和分母零点位置几乎相同. 关键词： 共振散射 模式缺损     

声学Mie共振及其应用

Mie共振是基于Mie散射理论的共振散射现象,起源于单极、偶极、四极、八极和更高的多极振子所引起的辐射叠加。近年来,人工产生的声学Mie共振得到了越来越多的关注。由于声学Mie共振具有多种共振模式,基于Mie共振的声学超构材料体现出许多独特的声学特性,有望被应用到低频声波强反射、负折射、彩虹俘获、指向性声辐射、超常声波透射等众多领域当中。     

固体中圆柱状界面处力学量边界条件和界面的物理模型

简要介绍了固体复合媒质中圆柱状界面层的声散射理论,给出了联系界面层内外表面处声场产生的位移和应力的传递矩阵。将此传递矩阵对界面层厚度作渐近展开,可得界面薄层处力学量一级和二级近似边界条件。当界面簿层厚度远小于圆柱散射体半径时,传递矩阵可进一步简化,这时的近似边界条件可用界面弹簧模型解释。以数值计算为例子,讨论了各种近似边界条件的有效性和可能应用。本文还考虑了界面状况对声散射的影响。最后指出了声与柱状界面薄层相互作用方面有待进一步研究的一些问题。     

基于石英柱模型的光子晶体光纤异常布里渊散射特性的理论研究

通过石英圆柱模型,理论研究了小芯径光子晶体光纤中混合声波模式的色散、模式耦合以及声光相互作用,理论计算出了布里渊散射增益系数谱的双峰结构及其随抽运光波长和温度的演化规律. 理论分析表明光子晶体光纤中布里渊散射增益系数谱的双峰结构源于小芯径光子晶体光纤中混合声波模式之间的模式耦合. 通过温度改变导致的材料参数变化对声波模式色散特性的影响,特别是声波模式耦合点的移动,解释了双峰结构随外界温度的变化规律. 并且,通过理论计算与实验结果的对比讨论了石英圆柱模型的局限性和适用范围. 关键词： 布里渊散射 声光相互作用 模式耦合 光子晶体光纤     

超声与固体中含气泡层的相互作用

本文利用固体层状媒质声反射模型,给出了固体中含气泡层声反射和透射系数的表达式,并由此导出沿固体中含气泡薄层对称和反对称模式界面波的特征方程式。本文还介绍了含气泡固体有效弹性模量的估算方法,文中给出的数值计算具体说明了气泡体积浓度和气泡层厚度对声反射系数、声透射系数以及反对称模式界面波传播速度的影响,本文的研究为根据声反射系数和界面波的传播速度的测量反演固体间气泡层的力学性能提供了理论依据。 关键词：     

含有周期球腔的黏弹性覆盖层消声性能分析

利用散射矩阵法分析了单个球状空腔在黏弹性橡胶中的Mie散射特性以及振动模式.以此为基础，利用多重散射法分析了不同背衬条件下，含有单层周期球状空腔的橡胶覆盖层(厚度为8mm)的消声性能.结果表明，单个球腔的径向共振对覆盖层的低频消声性能有重要贡献，覆盖薄层在共振区具有良好的消声性能.最后，设计了双层消声覆盖层(厚度为20mm)，有效拓展了消声带宽. 关键词： Mie散射 多重散射法 消声材料 声子晶体     

A study of damping in fiber-reinforced composites

Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η₁₁, η₂₂, η₁₂ and η₂₃ considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber-interphase-matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber-matrix interface is incorporated to evaluate its effect on η₁₁, η₂₂, η₁₂ and η₂₃ in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading.     

MRI study of Fickian, case II and anomalous diffusion of solvents into hydroxypropylmethylcellulose

Magnetic resonance imaging was used to investigate the diffusion and swelling processes of a hydroxypropylmethylcellulose (HPMC) matrix. Polymer in the form of a cylinder was hydrated in a water solvent with pH 2, 7, and 12 at 37 °C and monitored at equal intervals on a Bruker Avance 300 MHz spectrometer. The spatially resolved spin-spin relaxation times and spin densities together with the change in the dimension of the glass core of the polymer were determined for the HPMC tablets as a function of hydration times. FromT ₂ parameters, the solvent molecule mobility within the gel layer of the HPMC was estimated. All studied parameters allow the determination of the diffusion of the solvent into the HPMC matrix as Fickian diffusion for alkaline solvents, case II for acidic solvent, and anomalous diffusion for neutral solvent.     

Scattering of antiplane shear waves by layered circular elastic cylinder

An exact analytical solution for the scattering of antiplane elastic waves by a layered elastic circular cylinder is obtained. The solution and its degenerate cases are compared with other simpler models of circular cylindrical scatterers. The effects of the geometrical and physical properties of the interphase are studied. Numerical results confirm the existence of a resonance mode in which the scatterer's core undergoes a rigid-body motion when the outer layer of the scatterer is very compliant. This resonance mode has been attributed [Liu et al., Science 289, 1734 (2000)] to a new mechanism for the band gap formed in the extremely low frequency range for phononic crystals made of layered spherical scatterers. Numerical results also show the existence of a similar resonance mode when the outer layer of the scatterer has very high mass density.     

Circumferential resonance modes of solid elastic cylinders excited by obliquely incident acoustic waves

When an immersed solid elastic cylinder is insonified by an obliquely incident plane acoustic wave, some of the resonance modes of the cylinder are excited. These modes are directly related to the incidence angle of the insonifying wave. In this paper, the circumferential resonance modes of such immersed elastic cylinders are studied over a large range of incidence angles and frequencies and physical explanations are presented for singular features of the frequency-incidence angle plots. These features include the pairing of one axially guided mode with each transverse whispering gallery mode, the appearance of an anomalous pseudo-Rayleigh in the cylinder at incidence angles greater than the Rayleigh angle, and distortional effects of the longitudinal whispering gallery modes on the entire resonance spectrum of the cylinder. The physical explanations are derived from Resonance Scattering Theory (RST), which is employed to determine the interior displacement field of the cylinder and its dependence on insonification angle.     

Finite element analysis of the thermal residual stress distribution in the interphase of unidirectional fiber-reinforced resin matrix composites

By means of three-dimensional finite element method (FEM) which is based upon the micro-mechanical model of fiber-reinforced composites, this paper selects representative volume elements and studies the effect of the five factors, namely, cooling rate, matrix elasticity modulus, fiber elasticity modulus, interphase elasticity modulus and fiber volume fraction, on the interphase thermal residual stress and its distribution law in epoxy resin NPEF-170/unidirectional glass fiber composites. The results indicate that thermal residual stress is mainly distributed on the fiber and the matrix of neighboring interphase; the thermal residual stress on the fiber and the matrix declines as the distance to the interphase layer grows; and it tends to zero at the distance of 1.5 times the radius of the fiber away from the interphase. The increase in any of the four factors, namely, cooling rate, matrix elasticity modulus, fiber elasticity modulus, and fiber volume fraction would trigger the rise of thermal residual stress in epoxy resin NPEF-170/unidirectional glass fiber composites. The additional flexible interphase layer can eliminate and transfer thermal residual stress effectively, whose effectiveness mainly depends on the difference between interphase elasticity modulus and fiber elasticity modulus.     

Scattering and active acoustic control from a submerged piezoelectric-coupled orthotropic hollow cylinder

A general exact analysis for three-dimensional scattering of a time-harmonic plane-progressive sound wave obliquely incident upon an arbitrarily thick bilaminated circular hollow cylinder of infinite extent, which is composed of a cylindrically orthotropic axially polarized piezoelectric inner layer perfectly bonded to an orthotropic outer layer, is presented. An approximate laminate model in the context of the so-called state space formulation along with the classical T-matrix solution technique involving a system global transfer matrix is employed to solve for the unknown modal scattering and transmission coefficients. Numerical example is given for an air-filled and water-submerged two-layered elasto-piezoelectric hybrid (steel/PZT4) hollow cylinder insonified by an obliquely incident unit-amplitude plane sound wave. Following the acoustic resonance scattering theory (RST), the total form function amplitude together with the associated global scattering, the far-field inherent background, and the resonance scattering coefficients of the nth normal mode are computed as a function of dimensionless frequency for selected angles of incidence, piezoelectric layer thickness parameters, and electrical boundary conditions (i.e., open/closed circuit or active). Also, the electrical voltage coefficients required for partial or complete cancellation of the reflected sound field are calculated. Limiting cases are considered and good agreements with the solutions available in the literature are obtained.     

Acoustic resonance scattering from a multilayered cylindrical shell with imperfect bonding

The method of wave function expansion is adopted to study the three dimensional scattering of a time-harmonic plane progressive sound field obliquely incident upon a multi-layered hollow cylinder with interlaminar bonding imperfection. For the generality of solution, each layer is assumed to be cylindrically orthotropic. An approximate laminate model in the context of the modal state equations with variable coefficients along with the classical T-matrix solution technique is set up for each layer to solve for the unknown modal scattering and transmission coefficients. A linear spring model is used to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. Following the classic acoustic resonance scattering theory (RST), the scattered field and response to surface waves are determined by constructing the partial waves and obtaining the non-resonance (backgrounds) and resonance components. The solution is first used to investigate the effect of interlayer imperfection of an air-filled and water submerged bilaminate aluminium cylindrical shell on the resonances associated with various modes of wave propagation (i.e., symmetric/asymmetric Lamb waves, fluid-borne A-type waves, Rayleigh and Whispering Gallery waves) appearing in the backscattered spectrum, according to their polarization and state of stress. An illustrative numerical example is also given for a multi-layered (five-layered) cylindrical shell for which the stiffness of the adhesive interlayers is artificially varied. The sensitivity of resonance frequencies associated with higher mode numbers to the stiffness coefficients is demonstrated to be a good measure of the bonding strength. Limiting cases are considered and fair agreements with solutions available in the literature are established.     

三元合金缺陷层对有限超晶格中局域界面光学声子模的影响

在宏观介电连续近似下，采用转移距阵方法，研究了三元合金缺陷层对有限超晶格中局域界面光学声子模的影响.在这种有限超晶格结构中，可以清楚地看到所有界面模的演化轨迹.结果表明：存在两类局域模，它们的宏观静电势波函数分别局域在缺陷层和表面层附近，且这些模随着超晶格组分层和缺陷层的相对厚度和介电常数的改变，其局域位置和特性发生显著变化.此外，发现虽然能隙中局域模的数目不守恒，但所有界面模的总数守恒.     

Theory of ferromagnetic resonances in thin wires

A phenomenological theory of ferromagnetic resonances in a ferromagnetic metallic cylinder magnetized along its axis is based on the simultaneous solution of the equation of motion and Maxwell's equations. A general relaxation term in the equation of motion is used. The boundary conditions correspond to the dynamic surface anisotropy with the preferred direction parallel to the static magnetization. It is shown that the solution yields an infinite number of resonance modes of different spatial symmetry. Formulas for the surface impedance and the relative absorption of individual modes are derived. The effect of the finite radius of the cylinder on the resonance, antiresonance and spin wave resonance behaviour is discussed.     

Ferrimagnetic resonance spectra of magnetic bubble films at low microwave frequencies

Magnetic bubble films exhibit a number of ferrimagnetic resonance modes due to the spatial variation of the anisotropy. The resonance frequencies have been measured as a function of the applied bias fieldH ₀. In the lower field range the magnetization of the transient layer, which has negative anisotropy, is not yet parallel toH ₀. In this range the resonance frequencies are shifted to higher values due to pinning effects. In films grown by the vertical dipping method an additional layer on top of the transient layer is observed within which the magnetization rotates from the direction in the transient layer to that of the bulk of the film. In films grown by horizontal dipping no such layer could be detected. Each ferrimagnetic resonance mode excites transverse elastic waves in the film due to the magnetoelastic interaction and thus gives rise to elastic resonances of the whole crystal, film and substrate. These elastic resonances lead to a fine-structure of the ferrimagnetic resonances. The observed fine-structure vanishes periodically with frequency and from this behaviour the thickness of the magnetic film and of the transient layer has been determined.