THEORY OF THE EMA METHOD OF DETECTING RAYLEIGH WAVES FOR FERROMAGNETIC AND FERRIMAGNETIC MATERIALS.

The equations for the electrodynamics of a moving medium have been used in developing the theory of the EMA method of detecting Rayleigh waves in a ferromagnetic or ferrimagnetic polycrystalline medium polarized by a homogeneous steady magnetic field. Expressions are derived for the absolute and relative contributions of the main EMA mechanisms for various orientations of the polarizing field: the magnetostriction, magnetic, and current ones. It is shown that the current mechanism can play a substantial part for a ferromagnetic metal only for very strong polarizing fields, which are difficult to attain in practical designs of EMA transducers. The dominant contribution in a tangential polarizing field comes from the magnetostriction, while the magnetic mechanism predominates in a normal field.