Diffraction of Ultrasound in Elastically Anisotropic NaCl and in Some Other Materials

Ultrasonic diffraction in NaCl and KCl single crystals, as well as in steel, has been studied by the pulse-echo method from 8–45 Mc/sec with 12-in. disk transducers. The diffraction is of the Fresnel type, so that the curves of loss due to diffraction can be plotted with a normalized abscissa S = z/(a2/λ), where z is the path length in the specimen, a the transducer radius, and λ, the ultrasonic wavelength. In general, the loss curve is not monotonic in S. The shape of the curve is dependent upon the specimen material, the crystallographic direction of ultrasonic propagation, and the transducer plating configuration. The position of the last local maximum in the loss curve is a function of the anisotropy of the specimen. In particular, its position in steel (isotropic case) agrees with the theoretical position for isotropic materials.