超薄层状复合媒质弱界面深度与声导波

结合推导层状复合媒质各界面刚性联接时声导波频散特性方程的传递矩阵方法,以及滑移界 面边界条件和弱界面“弹簧”模型,分别导出了超薄层状复合媒质中存在不同深度弱界面、滑移界面和脱层情况下声导波的广义频散方程,分析了三种联接界面的深度对低模式声导波频散特性的影响. 关键词： 导波 界面 频散     

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。     

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。     

界面层对层状各向异性复合结构中Lamb波的影响

建立了各向异性界面层的弹簧模型,并将其应用于分析层状复合媒质的全局矩阵技术中.其 引入的机理是全局矩阵的程序结构、各层矩阵的排列不至于遭受大的破坏.因此,把弹簧界 面作为一个“材料层”.该层的材料常数用劲度常数来描述,其层厚为零.把该层放在全局矩 阵适当的位置而使系统中的其他层不发生任何变化.数值示例显示了刚性联接、滑移联接、 完全脱层三种不同界面条件下双层各向异性复合结构中Lamb波的频散特征,并对刚性联接和 滑移联接时质点沿板厚方向的位移分布进行了比较. 关键词： 各向异性界面 弹簧模型 全局矩阵 兰姆波频散     

有机层界面对双层有机发光二极管复合效率的影响

建立了双层有机发光二极管中载流子在有机层界面复合的无序跳跃理论模型.由于有机分子材料的空间及能带结构的无序性，采用刚体模型处理有机层界面问题是不恰当的，而采用无序跳跃模型比较合理.复合效率及复合电流由载流子跳跃距离、有机层界面的有效势垒高度及该界面处的电场强度分布所决定：在双层器件ITO/α-NPD/Alq₃/Al中，当所加电压小于19.5V时，复合效率随着载流子跳跃距离的增加而增加，而大于19.5V时，复合效率随着其距离的增加而减少；复合效率随着有机层界面有效势垒高度的增加而增加； 关键词： 有机层界面 双层有机发光二极管 复合效率 有效势垒高度 无序跳跃模型     

层状各向异性固体媒质的声反射和声透射

本文导出了联系任意对称的各向异性固体层上下界面力学量（位移和应力）的传递矩阵，从而提出了层状固体媒质声反射和声透射的一般模型，作为例子，本文数值计算了金属铝中双层正交对称固体（其间界面呈刚性联接或滑移联接）对声波的反射和透射系数。     

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。     

低温柱状等离子体传播特性的研究

分析了轴对称柱状等离子中波的传播特性,研究了表面波模式下的电磁波传播的色散关系,给出了波矢随等离子体参数、介电常数、结构尺寸、工作频率的变化曲线。结果表明,可以通过选择适当的等离子体参数、介电常数以及结构尺寸来控制波的传播特性。     

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．     

双层有机发光二极管中复合效率和复合区域宽度的研究

本文建立了双层有机发光二极管中载流子的注入、输运和复合的理论模型.模型中采用了较合理的无序跳跃模型来处理界面问题.计算和讨论了空穴传输层厚度和内界面处的空穴势垒对器件复合效率和复合区域宽度的影响.结果表明:器件结构的变化导致电场强度在器件中的重新分布,空穴传输层厚度和内界面处空穴势垒的变化对器件的复合效率和复合区域宽度有重要影响.     

LAMB WAVE MODES IN A TWO-LAYERED SOLID MEDIUM WITH A WEAK INTERFACE

Using the "spring" model for a weak interface between two solids, we derive the charac-teristic equation for the Lamb waves in a two-layered solid composite and make numerical computations for dispersion curves in an aluminum/copper structure with a rigid or slip interface. The influence of the shear stiffness of the interface on the low order Lamb wave modes is considered.     

Guided wave propagation and mode differentiation in hollow cylinders with viscoelastic coatings

Guided wave propagation theories have been widely explored for about one century. Earlier theories on single-layer elastic hollow cylinders have been very beneficial for practical nondestructive testing on piping and tubing systems. Guided wave flexural (nonaxisymmetric) modes in cylinders can be generated by a partial source loading or any nonaxisymmetric discontinuity. They are especially important for guided wave mode control and defect analysis. Previous investigations on guided wave propagation in multilayered hollow cylindrical structures mostly concentrate on the axisymmetric wave mode characteristics. In this paper, the problem of guided wave propagation in free hollow cylinders with viscoelastic coatings is solved by a semianalytical finite element (SAFE) method. Guided wave dispersion curves and attenuation characteristics for both axisymmetric and flexural modes are presented. Due to the fact that dispersion curve modes obtained from SAFE calculations are difficult to differentiate from each other, a mode sorting method is established to distinguish modes by their orthogonality. Theoretical proof of the orthogonality between guided wave modes in a viscoelastic coated hollow cylinder is provided. Wave structures are also calculated and discussed in view of wave mechanics in multilayered cylindrical structures containing viscoelastic materials.     

Frequency-wavenumber domain analysis of guided wavefields

Full wavefield measurements obtained with either an air-coupled transducer mounted on a scanning stage or a scanning laser vibrometer can be combined with effective signal and imaging processing algorithms to support characterization of guided waves as well as detection, localization and quantification of structural damage. These wavefield images contain a wealth of information that clearly shows details of guided waves as they propagate outward from the source, reflect from specimen boundaries, and scatter from discontinuities within the structure. The analysis of weaker scattered waves is facilitated by the removal of source waves and the separation of wave modes, which is effectively achieved via frequency-wavenumber domain filtering in conjunction with the subsequent analysis of the resulting residual signals. Incident wave removal highlights the presence and the location of weak scatterers, while the separation of individual guided wave modes allows the characterization of their separate contribution to the scattered field and the evaluation of mode conversion phenomena. The effectiveness of these methods is demonstrated through their application to detection of a delamination in a composite plate and detection of a crack emanating from a hole.     

谱有限元数值分析各向异性复合板中导波色散特性

提出谱有限元方法研究层状各向异性复合板中导波的色散特性和波结构。基于三维弹性动力学方程,用有限元方法离散波导截面,波传播方向的位移用简谐波表示,得到了导波色散的特征方程。分析了单层和双层复合板中导波沿不同方向传播的色散特性和波结构,讨论了双层复合板中层厚比对相速度的影响。数值研究结果表明:导波的对称模态沿纤维方向传播时在较宽的频率范围内保持弱色散状态。双层复合板中导波基本模态的相速度在低频时受层厚比的影响较明显,随着频率的增加趋向于相速度较低的材料。数值模拟结果为导波用于复合材料定量无损检测和性能评价提供理论依据。      

Damping properties of layered cylindrical shells,vibrating in axially symmetric modes

The damping of cylindrical shells coated with unconstrained layers of viscoelastic material either on one side of the shell (inside or outside) or on both sides is estimated. The basic equations of motion are derived which describe harmonic forced flexural damped vibrations in axisymmetric modes. For pure sinusoidal modes expressions for the overall loss factors are given. The damping properties of cylindrical shells of finite length, coated on the inside or outside, or on both sides (symmetrically or unsymmetrically) are compared. Classical thin shell theory is used for the analysis. It is shown how two-layered damped shells differ from two-layered damped beams. The extent of damping reduction in shells resulting from the fact that the shell cross-section is closed is discussed.     

Guided Waves in a Multi-Layered Cylindrical Elastic Solid Medium

We investigate the guided waves in a multi-layered cylindrical elastic solid medium. The dispersion function of guided waves is usually complex and the dispersion curves of all modes are not conveniently obtained. Here we present an effective method to obtain the dispersion curves of all modes. First, the dispersion function of the guided waves is transformed into a real function. The dispersion curves are then calculated for all the modes of the guided waves by the bisection method. The modes with the orders n = 0, 1, and 2 are analysed in two- and three-layer media. The existence condition of Stoneley wave is discussed. The modes of the guided waves are also investigated in a two-layer medium, in which the velocity of shear wave in the outer layer is less than that in the inner layer.     

Excitation mechanisms and dispersion characteristics of guided waves in multilayered cylindrical solid media

This paper first reviews a method of simulating the propagation characteristics of guided waves in multilayered coaxial cylindrical elastic solid media. Secondly, this method is used to investigate the properties of the guided waves for the ultrasonic long-range non-destructive evaluation techniques for rockbolts. To do so, the special case of non-leaky guided modes in open waveguides is considered. The method explains how the complex dispersion function is converted into a real function: hence the bisection technique can be employed to search for all the real roots. The model is used to (i) characterize the low dispersion range and anomalous dispersion of normal and Stoneley modes and (ii) analyze the excitation mechanisms of guided waves from axisymmetric and non-axisymmetric acoustic sources. The results are used to select suitable excitation frequency ranges associated with dominant modes with large amplitudes, low dispersion, and distinguishable propagation velocities to reduce signal distortion. The results suggest the lowest order flexural mode, excited by a radial force source, has potential to be used in practice. Also, the highly dispersive Stoneley mode propagating along a cylindrical interface is defined and distinguished from the normal mode using two properties, velocity high-frequency asymptotes and amplitude distributions along the radial direction.     

Cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate

The physical process of cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate is presented by using the second-order perturbation and the technique of nonlinear reflection of acoustic waves at an interface. In general, the cumulative second-harmonic generation of a dispersive guided wave propagation does not occur. However, the present paper shows that the second-harmonic of Lamb wave propagation arising from the nonlinear interaction of the partial bulk acoustic waves and the restriction of the three boundaries of the solid plates does have a cumulative growth effect if some conditions are satisfied. Through boundary condition and initial condition of excitation, the analytical expression of cumulative second-harmonic of Lamb waves propagation is determined. Numerical results show the cumulative effect of Lamb waves on second-harmonic field patterns.     

Fabrication and application of imaging holographic gratings (chirped gratings) for integrated optics

Holographic chirped gratings with parallel grating lines have been fabricated by recording the interference structure of a plane wave and a cylindrical wave in a photoresist layer on a monomode glass waveguide. These gratings will be useful elements for the imaging of guided waves in integrated optics. A theoretical approach for treating their imaging properties is presented. The experimental results are described theoretically.