Observables due to beam-to-mode conversion of a high-frequency Gaussian P-wave input in an aluminum plate in vacuum

Obliquely incident Gaussian P-wave inputs furnish important test signals for ultrasonic detection of flaws in layered elastic media. Unlike vertically impinging beams, multiply reflected oblique beams eventually are converted into guided modes. The horizontal ranges over which the field is beamlike or modelike must be well understood for selection of a diagnostic scheme with “good” features for detection and identification. An analytical study is conducted here to detail the beam-to-mode conversion and P-SV coupling processes in an aluminum plate. The rigorously based approach utilizes the complex source point (CSP) method for generation of the input beam, and offers ray, mode, and hybrid ray-mode alternatives for best characterization of the wave phenomena. Numerical reference results over a representative range of parameters, which furnish potentials and displacements in various cross sections and on the plate boundaries, are interpreted in terms of beam or mode observables and related to the spectral wavenumber content of the incident signal. These considerations lead to the formulation of certain rules that categorize the detected signal in a manner which may be helpful in the construction of inversion algorithms for flaw detection.