有液层负载时薄板中类Lamb波的传播

本文研究薄板一面有液层负载时板中类Ｌａｍｂ波的传播，从弹性波传播理论出发，导得了类Ｌａｍｂ波的色散方程。由于几何不对称，因此不可能严格区分出对称与反对称模式，而是耦合在一起。数值计算结果表明，板中类Ｌａｍｂ波相速度随液层厚度增加呈周期变化。当ｋｔｄ＜＜１时类反对称模式的相速度变化近似与液层厚度成正比，这与特征阻抗法结果相同。初步实验结果验证了上述理论。     

有液层负载时各向异性薄板中Lamb波的传播

研究各向异性板有液层负载时板中Ｌａｍｂ波的传播．以微传感领域常用的ＺｎＯ等为例,从弹性波传播理论出发,结合边界条件,导得了各向异性薄板有液层负载时板中Ｌａｍｂ波传播的色散方程,这也同样适用于正交晶体系,正方晶体系和立方晶体系的晶体．数值计算结果表明,各向异性板中Ｌａｍｂ波相速度随液层厚度增加呈周期变化．当单面有液层负载的薄板厚度２ｄ很小时,Ａ０模式的类Ｌａｍｂ波的微质量传感特性也作了讨论．     

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：     

有粒滞液层负载时薄板中类Lamb波的传播

本文从弹性波传播理论出发，结合边界条件，导出了薄板一面有粘滞液层负载时板中类Lamb波传播的色散方程；研究了液层粘滞引起的类Lamb波衰减．数值计算表明，板和液层的驻波共振振动引起极中类Lamb波对称和反对称模式的模式转换以及衰减系数的变化。文中对ktd《1时，Ao模式类Lamb波的微质量和粘滞传感特性也作了讨论。     

三层复合结构中的漏Lamb波：理论与实验

本文导出了具有流体负载的三层复合结构中漏Ｌａｍｂ波的特征方程，具体计算了铝／水／铝复合结构中漏Ｌａｍｂ波模式的色散和衰减特性，并与不存在流体负载时结构中经典的Ｌａｍｂ波传播特性作了比较。采用宽频带超声透射谱实验系统，测量了浸没在水中的铝／水／铝结构中的漏Ｌａｍｂ波色散关系。理论与实验结果符合较好。     

薄板中类Lamb波在负载流体中引起的声流的研究

板的一侧有粘滞液层负载时,板中类Lamb波的传播将会在其负载流体中引起声流。结合单面粘滞液层负载板中类Lamb波的传播机制以及流体中由于声波非线性传播引起声流的理论,运用逐级近似法,并考虑到具体的实验条件,计算了薄板内有类Lamb波传播时,其负载流体中声流的速度大小与分布。数值计算与已有实验符合较好。     

短路金属栅对正入射瑞利波的散射

由压电晶体动力学方程等出发,用电表面边界微扰技术得到了入射声表面波在栅区激发的微扰电场及电荷分布;将这些电荷作为表面激发源,用积分变换得到了包括散射声表面波和体波的一般积分解。数值计算了YZ-LiNbO_3,表面上短路金属栅对正入射瑞利波散射的声表面波,给出了其反射系数,前向散射系数等与栅条宽度的关系;进而导出了声表面波经过金属栅时的相速变化。理论计算与实验测量结果符合较好。     

固体板中SH型板波的“共振”二次谐波发生

从理论上研究了固体板内SH型板波的“共振”二次谐波发生。结果表明，当固体板内SH型板波的相速等于板材介质的纵波声速时，二阶驱动波表现出沿固体板界面方向积累的性质。根据二阶应力边界条件，确定出了固体板内的二阶积累波。尽管本文不能完全确定出板内的二阶平面波，但文中求得的固体板内伴随SH型板波传播所发生的二阶积累波，仍是具有实际意义的。     

激发双线波导中的对称和反对称等离子体波导模式的新型耦合器

在亚波长光学集成中,波导中表面等离子体传输模式的激发是一个重要的问题。利用表面全息法设计结构,并对表面等离子体波进行整形。将平面等离子体波匹配到双线波导中的对称和反对称模式,从而实现波导中两种模式的有效激发。利用时域有限差分法对设计结构进行验证,发现双线波导中两种模式能够有效激发。对结构参数进行优化,对称与反对称模式的激发效率分别达到8.7%和10.8%。     

声表面波介质表面受力条件下的波速变化研究

为了计算力负载直接作用在声表面波传播表面时波速的变化特性,通过有效材料系数将负载引入,并用广义Green函数计算声速,得到了数值计算的结果,并用声表面波谐振器进行了实验.实验结果表明,将力负载直接加载在声表面波的传播表面时,波速变化量和力负载大小近似为线性关系,该加载方式下,实验中声表面波谐振器的谐振频率对外加质量负载有较高的灵敏度,可达1900 Hz/g.     

The propagation of Lamb waves in a plate bordered with layers of a liquid.

The influence of liquid layers on the propagation of Lamb waves in a plate of finite thickness is studied theoretically. The dispersion equations of Lamb waves in a plate bordered with layers of liquids are derived. Numerical solutions of the equations show that the phase velocity of Lamb waves changes with the thickness of the liquid layers. For the lowest antisymmetrical mode of very thin plates, the numerical results calculated from the dispersion equations are compared with those derived from the bending wave acoustic impedance approach. The limitation of the latter is discussed. Applications of Lamb waves pertinent to biosensing are also presented.     

Study of the influence of thin layer loading on the propagation of Lamb waves using perturbation method

I.IntroductionSincethepublicationoftheclassicalpaper"Onthewavesinanelasticplate"byH.Lambin1917l1l,theterm"LaInbwave"hasbeenusedtorefertoanelasticdisturbancepropagatinginasolidplatewithfreeboundaries.Lambwavesarewidelyusedintheapplicationsofthedefectinspectionofthinwa.lledmaterial[2'8].InrecelltyearsLambwaveshavebeenwide1yusedinthefabricationofsensors.LamInwavesensorsdetectthechangesofenvironmentbymeasuringthechangeofphasevelocityofLambwaves.IncomparisonwithbuIkwavesandSAW's,Lambwavsprovi…     

Lamb wave propagation in three-layered composites

I.IntroductionThepropagationpropcrticsofLambwavesinasinglep1atchavebceninvestigatedwide1ysincel93o's,butthestudyofLambwavcsin1aycredsolidcompositesisre1ative1ynew.WuandZhuana1yzedthepropagationofLambwavcsinaso1idp1ateboundedbytwo1iquid1ayerswithidentica1thickncss.['lOntheothcrhand,L1oydandRedwoodstudiednumerica11yLambwavesinacompositeconsistingofa1iquidintcrmediate1ayerandtwosolidplates.['lInour'l,lwederivedthecharacteristicequationforLambwavesintwo-layeredsolidpreviouspaper,compositeswit…     

Mode selection of Lamb waves for the evaluation of solid plates with liquid loading

This paper studies the mode selection of Lamb waves for evaluating solid plates with liquid loading. For this purpose, the Lamb wave selected should have the features such as zero normal displacement components at the plate surface in contact with liquid, small dispersion, and maximum group velocity. It is found that when the phase velocity of Lamb wave is equal to the longitudinal wave velocity of the plate material, its normal displacement at the plate surface is always zero. Through the numerical analyses, the specific S₂ Lamb wave that has zero normal displacement component at the plate surface, small dispersion and maximum group velocity compared with the other Lamb waves has been found. With respect to the specific S₂ Lamb wave, some experimental examinations have been carried out. It is found that the liquid loading on the plate surface has less influence on the specific S₂ Lamb wave signal but it can effectively eliminate the other signals. Moreover, the specific S₂ Lamb wave selected exhibits the capability of detecting multiple defects in the solid plate with the liquid loading. It can be concluded that the specific S₂ Lamb wave selected is suitable for the evaluation of solid plates with liquid loading.     

采用单个压电传感器的单模式兰姆波激发频率的选择

考虑了压电传感器(PZT)与板之间的耦合作用,从理论上研究了单个压电传感器激发时产生单模式兰姆波的频率调节方法,实验给出了模式选择在兰姆波结构健康监测中的应用. 在板材、板厚以及PZT尺寸一定的情况下,从理论上能够预测到作为频率函数的各兰姆波模式的幅值变化. 根据某特定兰姆波模式的幅值最大而其他模式幅值相对最小时所对应的频率,即可识别出该兰姆波模式优化的激发频率. 数值仿真验证了理论的有效性以及单模式兰姆波选择的可能性. 在不同的激发频率下,分别激发了优化的A0 模式,优化的S0模式以及共存的A0和S0模 关键词： 兰姆波 压电传感器 激发频率 结构健康监测     

小样本字典学习的兰姆波模态识别方法*

针对兰姆波多模态识别问题,提出了基于小样本字典学习的模态识别方法。将多层复合板的频散特性看作一个线性时不变系统,首先,根据频散知识模拟各个模态传播特定距离后的信号,提取走时和能量特征创建字典;其次,获取待测信号的走时特征,通过查询字典来识别兰姆波模态;最后,根据能量参数估计结果,实现待测信号中各模态信号的分离和重构。通过对三层粘接的AAA板(铝板-亚克力板-铝板,每层厚度为2mm)中传播距离为0.3m、0.5m的直达波和反射波的实验验证,结果显示该方法对A0、S0模态的有效识别和各个波包信号的准确重建。     

SH wave propagation in a piezoelectric/piezomagnetic plate with an imperfect magnetoelectroelastic interface

In this paper, we investigate the SH wave propagation in a layered piezoelectric (PE) and piezomagnetic (PM) plate with an imperfect magnetoelectroelastic interface. A linear magnetoelectroelastic spring model is used to describe the weakness of the imperfect interface. On the basis of this model, dispersion curves and mode shapes of the SH waves are computed. In particular, a PZT-5A/CoFe₂O₄ composite plate is considered in the numerical examples to calculate the dispersion curves and the mode shapes for different combinations of the magnetic, electrical and elastic spring constants. The effects of the layer thickness ratio and the electric-magnetic boundary conditions on the dispersion curves are discussed in details. Our results show that for a general weak bonding case, the high modes of the dispersion curves are not monotonous in the range of small wave numbers. With the layer thickness ratio increasing, the wave velocities of the SH waves increase. The electric boundary conditions mainly determine the dispersion curves of the SH waves in the case of a small layer thickness ratio, i.e. a large thickness of the PE layer. The present results have relevant applications in the nondestructive testing and evaluation of the layered PE/PM plate-like wave devices.     

用于储罐底板缺陷检测的超声兰姆波模式研究

从超声兰姆波的声场方程出发,得到板材表面离面位移(法向位移)为零的条件,即当超声兰姆波的相速度等于板材介质的纵波声速时,在板材表面的离面位移为零。在给定适当频厚积的条件下,分别数值模拟了仅有切向位移而无离面位移的A1、S1、A2和S2兰姆波模式在有液体负载的单层钢板中的传播情形。结果表明:离面位移为零的S2模式频散较小且对板中缺陷更为敏感。     

铝板中Lamb波检测的实验研究

Lamb波在传播过程中具有频散及多模态特性,若相关参数选择不当,会导致在实际应用中信号相互叠加而无法识别。本文基于Lamb波的频散曲线是其频散方程实数解分布的特点,采用二分法绘制了铝板中Lamb波的频散曲线、波结构曲线和入射角曲线。根据曲线选择S0模态的Lamb波对1mm厚铝板中不同类型的缺陷进行检测。实验结果表明,S0模态的Lamb波对裂纹型缺陷和贯穿型缺陷十分敏感,但对于裂纹型缺陷,其幅值变化并不与缺陷大小成线性关系,并且S0模态Lamb波的声场指向性十分集中,在偏离声束轴线时无法检测到缺陷。     

The effect of surface stress on the propagation of Lamb waves

This work investigates the possibility of the propagation of Lamb waves in thin solid layers with external traction free surfaces, in the presence of surface elasticity, inertia and residual stress. It is demonstrated that such waves do exist and that their characteristics can be quite different from their classical counterparts. The governing equations with non-classical boundary conditions involving the bulk and surface stress are solved exactly in the frequency-wavenumber domain. This solution is utilized to compute the Lamb wave modes for different layer thicknesses. An efficient strategy to capture all the modes of Lamb waves within a given frequency window is outlined. It is shown that the effect of surface elasticity and inertia becomes significant with increasing frequency and decreasing layer thickness, where the number of modes participating within a given frequency window is more than that permitted by the classical theory. Further, it is observed that the nature of the Lamb wave modes (in terms of negative dispersion) in the presence of surface stress is similar to what predicted by the nonlocal theory and microstructure based continuum theory.