基底上覆分层薄膜超声Scholte波特性与薄膜定征

分层薄膜-基底结构广泛应用于微电子器件等诸多领域,但薄膜材料参数超声测量尤其是横波速度的定征是一个困难的问题。本文对液固界面Scholte界面波的频散特性和脉冲激励的声压响应进行了理论分析。结果表明,液固界面Scholte波频散与分层膜-基底结构的速度分布密切相关。薄膜材料各层的厚度和横波速度对界面波频散特性有显著影响。基于Scholte界面波的频散特性,提出了一种多层膜的多参数反演定征方法。首先针对理论信号进行薄膜参数反演,验证了该方法的可行性。后续对不同类型的多层膜材料样品进行了液固界面波激发与采集实验,实验信号的薄膜参数反演结果进一步验证了该方法的可行性和有效性。     

Scholte波与含泥沙两相流介质属性关系的分析及仿真验证

基于四种超声悬浮液模型Urick, Urick-Ament, HT, Mcclements分析了Scholte波在两相流体与多孔介质固体界面处的传播特性. 结合各模型的复波数表达式建立含泥沙流体-多孔介质固体界面波特征方程, 分析了Scholte波速与两相流体积含量、粒径等介质属性的关系. 通过仿真实验获得界面波信号, 运用时延估计获得Scholte波速与泥沙含量、粒径的关系, 发现所得的波速与Urick-Ament和HT理论有相对好的一致性. 关键词： Scholte波 两相流体 多孔介质 泥沙含量     

脉冲激光在镀层圆柱表面激发的表面波

分别从理论和实验上研究了脉冲激光在快、慢镀层圆柱表面激发的表面波声场.脉冲激光线源在镀层圆柱周向上激发超声波信号并利用激光干涉仪检测.对钢基底锌镀层圆柱和锡基底铜镀层圆柱试样表面波的理论频散和实验信号估计频散进行了比较,瞬态位移场则利用留数定理与FFT技术数值仿真得到并与实验波形进行对比.结果显示:理论频散和仿真波形与...     

流体/准饱和多孔介质中伪Scholte波的传播特性

研究流体/多孔介质界面Scholte波的传播特性对于水下勘探、地震工程等领域具有重要意义.本文基于Biot理论和等效流体模型,采用势函数方法,推导了描述有限厚度流体/准饱和多孔半空间远场界面波的特征方程和位移、孔压计算公式.在此基础上,分别以砂岩和松散沉积土为例,研究了流体/硬多孔介质和流体/软多孔介质两种情况下,可压缩流体层厚度和多孔介质饱和度对伪Scholte波传播特性的影响.结果表明：多孔介质软硬程度显著影响界面波的种类、相速度、位移和水压力分布;有限厚度流体/饱和多孔半空间界面处伪Scholte波相速度与界面波波长和流体厚度的比值有关;孔隙水中溶解的少量气体对剪切波的相速度的影响不大,对压缩波相速度、伪Scholte波相速度和孔隙水压力分布影响显著.     

北极冰-水耦合系统中声波传播特性

利用固体和流体介质中波传播理论,导出了冰-水两层复合结构中导波频散方程.进一步,利用二分法对频散方程进行了数值求解,得到了 w-k频散曲线(w与k分别为圆频率和波数),以及相速度和群速度频散曲线.结果表明:冰-水两层复合结构中导波由具有相同厚度水层和冰层中导波耦合而成,但与水层和冰层中导波频散曲线相比,复合结构中导波频...     

弱界面固体附层媒质中的类Rayleigh波

当半无限大固体媒质上有一层固体附加层时表面波是频散的。由界面的“准弹簧”模型,本文导出了有各向同性固体附加层时半无限大各向同性均匀媒质中弱界面情况下的类Ｒａｙｌｅｉｇｈ波的特征方程。文中给出了典型复合结构具有刚性联接界面、滑移联接界面和弱界面时类 Ｒａｙｌｅｉｇｈ波的色散曲线,分析了界面刚度系数对类 Ｒａｙｌｅｉｇｈ波传播速度的影响。数值计算的结果表明选择合适的参数可以由低频超声类Ｒａｙｌｅｉｇｈ进行涂层结构界面特性的无损评价。     

弱界面压电覆层复合结构中的声导波

建立压电覆层复合结构中声导波传播模型,结合弱界面“弹簧”模型,推导了压电覆层复合结构存在刚性、滑移联接界面等几种不同界面条件下声导波的广义频散方程,数值计算钛锆酸铅基压电陶瓷覆层复合结构在不同界面条件下声导波的频散曲线,分析了界面特性对导波传播相速度的影响。数值计算和分析表明为了能够有效地评价界面的特性,选择合适的声波模式和声波频率是非常重要的。实验结果验证了界面假设的有效性,为进一步深入研究以多模式声导波参量为基础的压电覆层复合结构界面特性参数反演方法提供了理论基础。     

流-固界面波的激光激发与光偏转检测

基于光偏转原理,研制了可用于流-固界面波探测的光纤传感装置.在此基础上,建立了以调Q Nd∶YAG激光为流-固界面波激发光源的实验系统.实验上探测了激光在空气-铝、水-铝和酒精-铝等界面上激发的界面波波形.根据实验波形,算得在这三种界面上的泄漏Rayleigh波和Scholte波的速度分别为2889 m/s和339 m/s、2916 m/s和1512 m/s、2872 m/s和1184 m/s,此实验值与理论计算值相比,偏差小于5％.     

非均匀饱含黏性流体孔隙介质中声波传播及井孔声场分析

声波在饱含流体孔隙介质中的传播特性与流体的黏滞性及孔隙介质的非均匀性密切相关.本文在Biot理论基础上,考虑了孔隙流体的剪切应力及孔隙结构的非均匀性,采用含黏性流体孔隙介质中的波动理论,研究了孔隙介质中四种体波的频散和衰减特性,分析了慢横波对快纵波转换散射的影响,进一步推导了孔隙地层井孔中的模式波及其声场的解析解,研究了非均匀孔隙介质中井孔模式波和波列的特征.研究结果表明,含黏性流体孔隙介质中存在慢横波,慢横波的频散很强,其传播特征受到介质孔隙度、渗透率及孔隙流体黏度的影响.在非均匀孔隙介质中,与慢横波相关的剪切应力平衡过程不仅导致快纵波的频散和衰减,还会影响井孔伪瑞利波及斯通利波的传播特征.本文的工作完善了孔隙介质中声波传播的物理机制,为孔隙地层井孔声波的解释与应用提供了理论指导.     

飞秒脉冲激光加热金属薄膜的理论和实验研究

超短脉冲激光加热可应用于研究材料中载能子之间的超快相互作用,同时也广泛应用于超快激光加工.此前人们提出的双温度模型和抛物一步模型都只能用于描述超短脉冲激光加热金属薄膜后热量传递过程的特定片段.基于双温度模型和傅里叶导热定律,提出普适的理论模型可用于完整描述飞秒激光加热金属薄膜/基底时的整个热量传递过程.同时在300 K温度下,采用背面抽运-表面探测瞬态热反射法实验研究了飞秒脉冲激光加热金属薄膜的热量传递过程,理论预测曲线和实验测量结果符合较好,验证了理论模型的正确性.基于此模型测量得到了金薄膜的电子-声子 关键词： 飞秒脉冲激光 电子-声子耦合 界面热导 瞬态热反射     

Dispersion of interface waves in sediments with power-law shear speed profiles. I. Exact and approximate analytical results.

In the upper tens of meters of ocean bottom, unconsolidated marine sediments consisting of clay, silt, or fine sand with high porosity are "almost incompressible" in the sense that the shear wave velocity is much smaller than the compressional wave velocity. The shear velocity has very large gradients close to the ocean floor leading to strong coupling of compressional and shear waves in such "soft" sediments. The weak compressibility opens an avenue for developing a theory of elastic wave propagation in continuously stratified soft sediments that fully accounts for the coupling. Elastic waves in soft sediments consist of "fast" waves propagating with velocities close to the compressional velocity and "slow" waves propagating with velocities on the order of the shear velocity. For the slow waves, the theory predicts the existence of surface waves at the ocean-sediment boundary. In the important special case of the power-law depth-dependence of shear rigidity, phase and group velocities of the interface waves are shown to scale as a certain power of frequency. An explicit, exact solution was obtained for the surface waves in sediments characterized by constant density and a linear increase of shear rigidity with depth, that is, for the case of shear speed proportional to the square root of the depth below the sediment-water interface. Asymptotic and perturbation techniques were used to extend the result to more general environments. Theoretical dispersion relations agreed well with numerical simulations and available experimental data and, as demonstrated in a companion paper [D. M. F. Chapman and O. A. Godin, J. Acoust. Soc. Am 110, 1908 (2001)] led to a simple and robust inversion of interface wave travel times for shear velocity profiles in the sediment.     

Characteristic features of the velocity dispersion of surface acoustic waves in anisotropic coated solids

Basic patterns of the velocity versus wavenumber dispersion of the surface waves in solids coated by a relatively light or dense, "slow" or "fast" layer are discussed in the general case of an arbitrary anisotropy of substrate and coating materials. The onset of the subsonic wave branch, characterized by either a speeding or a slowing trend, is examined. Competitive tendencies, which pertain to the low-frequency dispersion in the case of dense "fast" layer, are revealed.     

Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone

Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone.     

Investigation of solid/solid interface waves with laser ultrasonics

A new method for detection of the soild/soild interface wave with laser ultrasonics is introduced in this paper. Based on the interaction between the acoustic wave and the probe laser beam of an interferometer in a transparent solid, the Stoneley waves propagated along the quartz/steel interface are detected successfully. The dispersion properties of Leaky Rayleigh wave are studied when the boundary conditions are described by interface spring mode. The Leaky Rayleigh wave at Plexiglas/aluminum interface is also detected and the experimental results are in good agreement with the theoretical results. It shows that the interface wave should be a powerful technique for evaluation of the interface properties.     

Quasidislocation stoneley wave and Eshelby dislocation Scholte wave

A quasidislocation (a dislocationlike entity described here for the first time) moves at the speed of a Stoneley surface wave that travels at the interface between two different elastic solids. An Eshelby glide edge dislocation moves at the speed of a Scholte surface wave that travels at the interface between a solid and an ideal liquid. The quasidislocation and the glide edge dislocation (that moves at the Eshelby velocity) are the Green's functions of their waves. Scholte waves are planar distributions of transonic moving glide edge dislocations. They are not Stoneley waves, although often called by that name, because Stoneley waves are planar distributions of subsonic moving quasidislocations.     

Reflection of structural waves at a solid/liquid interface

This paper investigates the reflection characteristics of structural or guided waves in rods at a solid/liquid interface. Structural waves, whose wavelengths are much larger than the diameter of the rod, are described in a first approximation by classical one-dimensional wave theory. The reflection characteristics of such waves at a solid/liquid (melting) interface has been reported by two different ultrasonic measurement techniques: first, measuring the fast regression rate of a melting interface during the burning of metal rod samples in an oxygen-enriched environment, and second, monitoring the propagation of the solid/liquid interface during the slow melting and solidification of a rod sample in a furnace. The second work clearly shows that the major reflection occurs from the solid/liquid interface and not the liquid/gas interface as predicted by plane longitudinal wave reflectivity theory. The present work confirms this observation by reporting on the results of some specially designed experiments to identify the main interface of reflection for structural waves in rods. Hence, it helps in explaining the fundamental discrepancy between the reflection characteristics at a solid/liquid interface between low frequency structural waves and high frequency bulk waves, and confirms that the detected echo within a burning metallic rod clearly represents a reflection from the solid/liquid interface.     

Fast compressional wave attenuation and dispersion due to conversion scattering into slow shear waves in randomly heterogeneous porous media

Within the viscosity-extended Biot framework of wave propagation in porous media, the existence of a slow shear wave mode with non-vanishing velocity is predicted. It is a highly diffusive shear mode wherein the two constituent phases essentially undergo out-of-phase shear motions (slow shear wave). In order to elucidate the interaction of this wave mode with propagating wave fields in an inhomogeneous medium the process of conversion scattering from fast compressional waves into slow shear waves is analyzed using the method of statistical smoothing in randomly heterogeneous poroelastic media. The result is a complex wave number of a coherent plane compressional wave propagating in a dynamic-equivalent homogeneous medium. Analysis of the results shows that the conversion scattering process draws energy from the propagating wave and therefore leads to attenuation and phase velocity dispersion. Attenuation and dispersion characteristics are typical for a relaxation process, in this case shear stress relaxation. The mechanism of conversion scattering into the slow shear wave is associated with the development of viscous boundary layers in the transition from the viscosity-dominated to inertial regime in a macroscopically homogeneous poroelastic solid.     

Shear waves guided by the imperfect interface of two magnetoelectric materials

In this paper, propagation of shear waves along a weak interface of two dissimilar magnetoelectric or magnetoelectroelastic materials is considered. Two exact dispersion relations are obtained for an imperfect electrode interface and an unelectroded interface, respectively. The existence condition of the interfacial waves is studied. Our results show that the interfacial imperfection strongly affects the velocity of the interfacial shear waves. In particular, for certain bi-magnetoelectric material, the interfacial shear waves may do not exist for a perfect interface and exist only for an imperfect interface. These findings are useful for the design of high-frequency wave devices.     

Propagation of magnetoacoustic surface waves along static plasma slab surrounded by moving plasma and neutral gas

The existence and propagation of fast and slow magnetoacoustic surface waves (MASW) is investigated in our work by taking a theoretical model of a static plasma slab as the middle layer with a moving plasma region at the top and neutral gas medium as the bottom layer. Applying linear MHD, the dispersion relation is obtained and the propagation of magnetoacoustic surface waves, in the compressional limit for steady flow and for different values of dimensionless wave numbers, is analyzed. Steady flow of plasma along a structured atmosphere may cause enhancement of existing surface modes, disappearance of some modes and generation of new surface wave modes. The possible regions for the propagation of fast and slow surface and body waves for different mass density ratios and magnetic field ratios and with a small flow velocity are studied. Our discussion may help in analyzing more complicated cases.