Diffraction of Ultrasound Radiating into an Elastically Anisotropic Medium

Abstract

The diffraction loss-distance characteristics in crystals have been computed for the single-slit transducer geometry in ultrasonic pulse-echo measurements. The characteristics are functions of elastic anisotropy and show several local maxima and minima before becoming monotonic at large distances from the transducer. By applying scale factors to the ordinates and abscissas of the characteristics, they were made applicable to the case of a circular transducer. The scale factors were chosen to bring the computed single-slit characteristic for isotropic materials into coincidence with the well-known isotropic-diffraction characteristic for circular-piston sources. The scaled crystal characteristics served to predict the positions of the local loss maxima to 15% and their amplitudes to 25% or better in four experiments. Certain crystals produce less diffraction loss per unit length than others because of the dependence of diffraction on anisotropy. The scaled diffraction loss-distance characteristics can be used for computing diffraction corrections for ultrasonic attenuation.