Lamb Modes In Plate Research Articles

Minimum-Variance Imaging in Plates Using Guided-Wave-Mode Beamforming.

This article presents improvements to ultrasonic imaging of solid platelike structures using the minimum-variance distortionless response (MVDR) beamforming processor. The primary application of this work is in the nondestructive testing (NDT) of platelike components that are widely used in aerospace, marine, and civil structures. The study proposes a new set of weights, or MVDR replica vectors, that are based on the physics of the propagating Lamb modes, including the symmetric mode S0, the antisymmetric mode A0, and the shear horizontal mode SH0. Numerical results show that these wave-mode weights, combined with geometrical spreading, improve the focus of the array by increasing the dynamic range and the spatial resolution of the image. In addition, quite dramatic improvements in image quality are achieved by combining, or compounding, the multiple Lamb modes naturally present in the plate in both transmission and reflection. As shown in recent work applied to bulk waves in 3-D solids, the compounding of Lamb modes in plates increases the array gain without increasing its physical aperture.

A simple formula for the longitudinal modes in a cylinder.

For CT<C<CL, the Pochhammer dispersion relation can be replaced by an approximate equation which can be solved to obtain the dimensionless wave number explicitly as a function of the phase velocity. This equation is similar to the corresponding equation for the Lamb modes in plate. The two types of modes are interlaced, i.e., between every pair of modes of the plate there is a longitudinal mode of cylinder and vice versa.