Effect of an acoustic wave on the surface impedance of a conductor

A solution is obtained for the problem of reflection of an electromagnetic wave of frequency ω1 from a conductor in which a sound wave of frequency ω2 with displacement vector normal to the surface is excited. The case of specular reflection of electrons by the surface of the conductor and an isotropic dispersion relation is considered. An anomalous skin effect is assumed to occur. The sound wave is shown to change the surface impedance of the conductor. If ω2 ≠ 2 ω1, the correction to the impedance is quadratic in the amplitude of the acoustic wave for low sound intensities. When the frequencies ω1 and ω2 are smaller than, or of the same order as, the collision frequency, and the sound wavelength is of the order of the skin depth at the frequency ω1, the correction ceases to be small in comparison with the linear impedance if the characteristic frequency of electrons trapped by the effective potential field of the acoustic wave becomes greater than the collision frequency.