Notes on microwave ferromagnetics research

Abstract

The paper is a report on several of the research projects undertaken in the Radio Research Department of the Bell Laboratories.Ceramic Ferroxdure has been studied at 9, 24 and 48kMc/s, and it has been established that the strong absorption at 48kMc/s is due to resonance caused by a crystalline-anisotropy field of 18000 oersteds. This material has been used as a filter, as the active element in millimeter-wave field-displacement isolators, and as a broad-banding element in a 24kMc/s Faraday rotator.Broad-banding of Faraday rotators has also been carried out by using a dielectric cylinder surrounding the ferrite rod. Such an element has been used to build a circulator giving good performance from 10.7 to 11kMc/s.Rectangular-waveguide resonance isolators have previously either yielded poor reverse-to-forward attenuation ratios, or provided very little reverse attenuation. By using dielectric loading adjacent to the ferrite element, it has been possible to obtain ratios of about 100 : 1 and reverse losses of more than 20dB per inch at 11kMc/s.Studies have been made of the changes in pulse shape and attenuation which occur when ferrite devices are driven by power at kilowatt levels. Some of the results confirm the new spin-wave theory of non-linear ferrite behaviour proposed by Suhl and Anderson.A circulator employing ferrite-loaded coupled waveguides has been constructed for the first time and the idea has been proved feasible. This type of circulator may possess an advantage in high-power applications, since the full power is not applied to the ferrite.A Faraday-rotation switch has been built for 58kMc/s which is capable of turning transmission on or off in 1 microsec. This shows promise for radar and modulator applications.