ELECTROMAGNETIC GENERATION OF ULTRASONIC WAVES IN METALS

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. © 1969, Acoustical Society of America. All rights reserved.