Separation of Leaky Lamb Modes for Ultrasonic Evaluation of Multilayer Structures

Ultrasonic guided Lamb waves are a major tool for nondestructive evaluation of cylindrically layered, fluid–loaded, elastic structures. When used in fluid–immersed steel pipes with a frequency–thickness product in the range of 1 to 3 MHz mm, fundamental pseudo–Lamb modes – the antisymmetric flexural and symmetric extensional modes –interfere and complicate the evaluation of elastic properties of an inaccessible medium outside of a pipe. We examine two techniques designed to separate the flexural mode from mixed leaky modes. Both techniques, a mode decomposition algorithm and a pursuit algorithm, are tested on synthetic and experimental data.