NONLINEAR ELECTROMAGNETIC GENERATION OF SOUND IN A METAL PLATE

The bilateral nonlinear electromagnetic excitation of longitudinal ult rasound in a metal plate is investigated theoretically. We considered a plate placed in a magnetic field h0 parallel to its surfaces, with t he conditions for the anomalous skin effect satisfied. The sound gener ation is due to the deformation and induction mechanisms of the electr on-phonon interaction. The mechanism of nonlinearity is magnetodynamic : it is related to the influence of the radio-wave magnetic field on c onduction-electron dynamics. It is demonstrated that even in a massive sample the singularities of acoustic oscillations on the plate faces are determined principally by the sound excited directly in the skin l ayer and, also, by the multiple reflection of sound waves from the sam ple boundaries. As a result, the role of the deformation mechanism of interaction increases notably. In the case of developed nonlinearity t he sound vibrations represent a very complex superposition of sharp ju mps with series of sharp spikes. The number of spikes in a radio-wave period depends on the sound damping, and increases considerably when t he damping decreases. Because of the formation of the standing sound w ave in the metal, each harmonic has a spatial resonance. The evolution of the hysteresis of the sound field, as a function of the external f ield h0, with increasing amplitude of the exciting radio wave is studi ed.