Magnetic Dispersion of Iron Oxides at Centimetre Wave-lengths

Abstract

THE electromagnetic properties of ferroso-ferric oxide and gamma-ferric oxide have been measured at wave-lengths of 9, 6 and 3 cm. The oxides in powder form were mixed in various proportions with a low-loss, non-magnetic binder, paraffin wax. Moulded specimens of the mixtures were inserted in a slotted transmission line (coaxial line at 9 cm. and 6 cm. : H₁₀ rectangular wave-guide at 3 cm.) fitted with a movable crystal detector probe, and measurements were made of the input impedances of the specimens when terminated in a short-circuit, and in an open-circuit (obtained experimentally by terminating in a short-circuited quarter wave-length line). The input impedance was derived from the voltage standing wave ratio n and the position of the voltage minimum. n was obtained indirectly from the relation n² = 1 + cosec² βx, where β is the phase velocity in the measuring line, and x the distance between points at which the high-frequency voltage is âš2 of its value at the minimum. In this way all measurements were carried out with crystal currents of less than 1·2 microamp., a range in which they were accurately proportional to the square of the high-frequency voltage.