Ultrasonic diffraction of microwaves in magnetized ferrite


  • R. S. Mueller


A description of the phenomena of ultrasonic diffraction of electromagnetic microwaves in a transversely magnetized ferrite slab is accomplished by the partial wave approach. Starting with the Lorentz-Lorenz law, the strength of the scattering is shown to be due to the change in the permittivity of an yttrium-iron garnet (YIG) ferrite at frequencies in the X band and above. When traveling sound waves act like a phase grating, the normal type of ultrasonic microwave diffraction occurs. The spacing and intensities of the orders of spectra are given by the Raman-Nath theory. Since the direction of magnetization is perpendicular to the direction of propagation, there are H and E waves that may propagate independently through the ferrite. Each wave has its own wavelength and direction of propagation. Two sets of upper and lower sidebands appear as right and left spectra to the primary H and E waves with equal intensity for the same order. Time variations of the refraction index are obtained by propagating ultrasonic energy as standing waves in a ferrite diffraction cell. The density variations associated with this sound wave result in a bending of a narrow microwave beam. For plane acoustic waves the horizontal beam deflection traces a vertical linear path.