Microwave Properties of Ferrites

Abstract

Microwave properties of many ferrites have been measured using a novel method of measurement. The sample is a slab 2×0.3×0.04 in. and the sample holder is a ridge waveguide resonant cavity. Measurements were made at five or more resonant frequencies occurring between 4 and 10 GHz. It was thus possible to make measurements over a wide range of frequency without changing sample or sample holder. Since the filling factor approaches unity, considerably greater sensitivity and accuracy can be obtained than is possible with the conventional perturbation methods. Samples measured included garnets, and nickel, magnesium, and lithium spinels. 4πMs ranged from 750 to 5000 G. Magnetic susceptibility of unmagnetized ferrites: The test data indicates an approximate empirical formula for the real part, given by χ′ = −0.34[γ(4πMs+Ha) /ω]2 at frequencies where the quantity in the square brackets is one or less. The loss component decreases with frequency and the curves have a variety of shapes. Dielectric loss tangent: When the dielectric loss tangent is low (less than 0.0007), it does not vary with frequency; for larger values, it generally decreases with increasing frequency. Measurement accuracy is estimated at ±0.0001 or ±3%, whichever is higher.