Specific Features of Excitation and Propagation of Longitudinal and Transverse Subsurface Waves in Solids: II. Effects of Some Boundary Conditions on Formation of Acoustic Fields

摘要

Modification of boundary conditions for propagation of transverse and longitudinal subsurface waves by covering a specimen's boundary surface with a layer of liquid may significantly affect amplitude P_A and the form and directivity characteristic (DC) of a subsurface wave (SW) source in a near-surface zone even in the case when the ratio of acoustic impedances of coupling media is m_(12) approx = 0.1. Dependences of the wave amplitude and the DC of probes of transverse and longitudinal SWs on geometric parameters of a rectangular protrusion located on the surface of the inspected solid body and on the wave frequency are established. The DC of a transverse-SW source has two global maxima located in the volume of the raised area and beneath it. These maxima are due to superposition of the fields belonging to the principal ST mode and to an additional mode transformed on the protrusion's edge. The studies performed have shown an increase in the sensitivity to flaws located beneath the extension of the coupling surface's plane in the protrusion's volume or above it.