Ultrasonic attenuation in copper and copper-aluminum samples is measured as a function of frequency and average grain size. At low frequencies the attenuation scales quadratically with the frequency and linearly with average grain size. In addition, there is a large difference in attenuation between powder metallurgy samples and cast-and-wrought samples, although their qualitative behaviors are similar both in terms of frequency dependence and grain size dependence. Such difference and the discrepancy with the existing theory may point to mechanisms of scattering by grain boundaries that are not included in the current theoretical model.

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The ultrasonic frequency spectrum is interpreted by Fourier analysis techniques. This approach leads to the same conclusions concerning flaw characterization as previous interference models; in addition, a number of other spectral characteristics are easily explained. Finally, the present treatment indicates that frequency analysis may be applicable to many additional problems, viz., timing measurements of any type (e.g., thickness or velocity measurements), wide-band attenuation measurements, and phase-shift measurements (e.g., determination of relative acoustic impedance). Subject Classification: 35.65, 35.80; 20.50.

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