Showing papers on "Guided wave testing published in 1969"
TL;DR: In this article, the diffraction of a plane light wave incident obliquely upon an isotropic dielectric layer traversed longitudinally by an acoustic microwave is examined by means of a guided-wave approach.
Abstract: The diffraction of a plane light wave incident obliquely upon an isotropic dielectric layer traversed longitudinally by an acoustic microwave is examined by means of a guided-wave approach. In addition to a considerable amount of physical insight, this approach provides a wide range of techniques that have already been developed extensively in the area of electromagnetic microwaves. As a consequence, available methods can be used to explain and express known aspects of the diffracted light in terms of simple guided-wave concepts which are applied herein to derive results that have not been available. It is shown that the difracted field within the dielectric layer, as well as in the exterior (air) medium, can be described by means of two alternative modal representations: 1) a description in terms of characteristic modes which progress independently of each other, and 2) a description in terms of coupled modes which interact with each other in the presence of the acoustic wave. While the two representations are equivalent, each has its own advantages and both are discussed in detail. It is also shown that these representations lead to equivalent networks that may be utilized to account for boundary conditions and for other features of the scattered field. In particular, diffraction phenomena in a Bragg regime are carefully investigated; qualitative and quantitative results are presented for situations wherein the orientation of the optic-acoustic interaction occurs at a Bragg angle of arbitrary order.
51 citations
TL;DR: In this article, a method employing video pulses to establish the proper cyclic match for rf measurements has been developed to supplement or replace the McSkimin ΔT criterion in all cases including those of adverse specimen geometry.
Abstract: Multimode guided‐wave patterns in bounded ultrasonic specimens have been shown to interfere with phase delay measurements made by the pulse superposition method and the pulse‐echo‐overlap method. The phase shifts associated with the nodes in the multimode guided wave patterns invalidate the McSkimin ΔT criterion for the choice of the proper cyclic matching between echoes when the nodes are near the echoes used. The adverse effect of nodes upon the McSkimin criterion has been documented by extensive measurements employing shear waves in square barsand thick plates. In free‐wave propagation without nodes, the ΔT criterion remains valid. A method employing video pulses to establish the proper cyclic match for rf measurements has been developed to supplement or replace the McSkimin ΔT criterion in all cases including those of adverse specimen geometry. Advantages and limitations of the video overlap criterion are discussed.
22 citations