Lamb wave scattering from a through hole

Ultrasonic guided waves, Lamb waves, are useful for evaluating the integrity of plate and shell structures common in many applications. Tomographic reconstruction with Lamb waves allows for the accurate reconstruction of the variation of quantities of interest throughout the investigated region, and it presents the data as a quantitative map. The location, shape, and extent of flaws can then be easily extracted from this tomographic image. The scattering of Lamb waves from severe flaws introduces artifacts in such reconstructions, however. In this paper higher order plate theory is used to derive analytical solutions for the scattering of the lowest order symmetric Lamb waves from a circular inclusion, focusing in particular on isolated through holes in plates. Plane wave and point source scattering behavior is explored for holes of different diameters, and a finite-beam solution is constructed by superposition of point source solutions. These results are then used to explain the scattering effects seen in Lamb wave contact scanning tomographic reconstructions. (C) 1999 Academic Press.