Electromagnetic Generation of Ultrasonic Waves in Metals

Abstract

The electromagnetic generation of pure shear and quasicompressional sound waves in metals for propagation, respectively, parallel to and perpendicular to a static magnetic field is investigated for a wide temperature range. Using a semiclassical model of a free electron gas moving against a positive ion background carrying the sound wave, the magnitude of the ionic displacements in the helicon geometry is calculated, together with the propagation constants. In the long-wavelength limit, the excited mode that propagates differs only slightly from a normal acoustic shear mode. Satisfactory agreement is obtained when these calculations are compared with our experimental results at room temperature, 77° and 4.2°K in static magnetic fields of up to 100 kG.