The velocity of sound for both transverse and longitudinal waves has been measured in single crystals of pure gallium. These velocity data have been used to calculate a complete set of elastic constants for gallium at 273, 77, and 4.2 °K. A survey has also been made of the acoustic attenuation in gallium at approximately 5 MHz over the range 1.5–300 °K. The measurements were made using a transducerless method which utilizes the direct electromagnetic generation of acoustic waves at the surfaces of a metal to excite standing sound waves in a slab-shaped specimen. It is demonstrated that this technique is both convenient and sensitive: changes of 1:106 in the velocity of sound in gallium were found to be readily measurable over the range 1.5–300 °K.

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A macroscopic theory is presented to explain the electromagnetic generation of acoustic waves in a metal in the presence of a steady magnetic field, and to account for the effect of these acoustic waves on the surface impedance. The theory is valid for the limiting case where the skin depth is much smaller than the wavelength of sound. In particular, the size and shape of the surface impedance singularities at frequencies corresponding to the formation of standing acoustic waves in a metal plate are calculated. Absolute measurements of the surface resistance and reactance of gallium single crystals are reported which are in quantitative agreement with the predictions of the theory.

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