IEEE Trans Ultrason Ferroelectr Freq Control. 2017 Oct;64(10):1558-1572. doi: 10.1109/TUFFC.2017.2719627. Epub 2017 Jun 26.
Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave applications, and to estimate wall thickness, corrosion, or sound velocities in plates and pipes. In such structures, measured ultrasonic transmission through the solid material is affected by acoustic beam diffraction effects, and the results may deviate from plane-wave descriptions, which are insufficient to describe the complex effects that occur. When exciting a fluid-embedded steel plate with a pulsed ultrasonic beam at normal incidence, resonance frequency downshift, axial sound pressure level increase, and beam narrowing have been observed, for measured resonance peaks in the frequency regions of certain leaky Lamb mode branches of the plate. In the ranges of other leaky Lamb mode branches, the observed effects are different. Measurements, finite element, and angular spectrum modeling are used to indicate a close connection between these beam diffraction phenomena and the backward wave characteristics of certain leaky Lamb mode pairs, in the frequency and Poisson's ratio regions around coincidence of two Lamb mode cutoff frequencies of similar symmetry. In particular, such observations made for the steel plate's fundamental thickness-extensional (TE) mode appear to be caused by acoustic beam excitation of the backward wave regions of the S and S leaky Lamb modes.
平面波理论常用于超声导波应用中，以估计板和管中的壁厚、腐蚀或声速。在这种结构中，通过固体材料测量的超声传输受到声束衍射效应的影响，结果可能偏离平面波描述，这不足以描述发生的复杂效应。当用脉冲超声束以正入射激励嵌入流体的钢板时，已经观察到共振频率下降、轴向声压级增加和波束变窄，这是在板的某些泄漏兰姆模式分支的频率区域中测量的共振峰的情况。在其他泄漏兰姆模式分支的范围内，观察到的效果不同。测量、有限元分析和角谱建模表明，在两个类似对称性的兰姆模式截止频率重合的频率和泊松比区域，这些波束衍射现象与某些泄漏兰姆模式对的反向波特性之间存在密切联系。特别是，对于钢板基本厚度拉伸（TE）模式的观察结果似乎是由 S 和 S 泄漏兰姆模式的反向波区域的声束激励引起的。
