Acoustic size effect and sound-attenuation anisotropy in layered metallic structures

The frequency and angular dependences of the sound attenuation in layered structures ...NINI... and ...NSNS... (N is a normal metal, S is a superconductor, and I is a dielectric) are investigated theoretically. The possibility of simplifying Maxwell’s equations for sound-induced electric fields in a metal is analyzed. A sharp anisotropy of sound attenuation due to the quasi-two-dimensional character of motion of electronic excitations in layered structures is found in the region of strong spatial dispersion. “Giant” oscillations of sound attenuation are found for the .....NINI..... structure, corresponding to commensurability of normal layer thickness and sound wave length.