Diffraction of a finite amplitude ultrasonic wave in solids

Abstract

In order to use the harmonic generation technique to measure the nonlinearity parameters of solids, one must determine the amplitudes of both the fundamental and the second harmonic of an initially sinusoidal ultrasonic wave. In our experiment performed at 30 MHz, a typical value of the fundamental amplitude is 1 Å with a second harmonic amplitude of 0.001 Å. Since interesting samples often are smaller than those in which the infinite plane-wave model is sufficiently accurate, we consider the effect of diffraction on the measurements. Ten transducers having diameters between 1.9 mm and 12.7 mm (∼10λ and ∼90λ) were used with the same [100] copper sample. The resulting data show that diffraction does influence the calculated amplitude with the smaller transducers. Interpretation of the data in terms of a nonlinear diffraction model is attempted. Theoretical considerations are discussed. [Research supported by the Office of Naval Research.]