DIFFRACTION LOSS IN THE [110] DIRECTION IN CUBIC-CRYSTALS

A new ultrasonic measurement model using an angular spectrum of plane waves operating upon a Gauss-Hermite expansion of the transducer field has been used to explain the ultrasonic diffraction loss in the [110] direction in cubic crystals. In the [110] direction, the slowness surface exhibits a saddle point. Previous theories for numerical integration could accommodate only parabolas of revolution for the slowness surface in the direction of propagation. The new theory agrees with previously published results in [110] Si, Ge, and NaCl. On the curves of loss versus normalized distance S, the positions along S of characteristics of the curves such as peaks, plateaus, and points of inflection are predicted to within experimental accuracy of 2%-5%. The magnitude of the loss is overestimated by as much as a factor of 2 relative to experiments, but it is thought that part of the discrepancy may lie in the experiments. The operation of the new theory was first checked against previously agreeing experiments and theories in the [100] and [111] directions in cubic crystals and in isotropic media. © 1990, Acoustical Society of America. All rights reserved.