Some properties and applications of ferrites at 3 cm wavelength

Abstract
The effect of temperature on some of the properties of ferrites in WG16 rectangular waveguide has been studied between 20 and 300°C. The properties investigated were the zero-field loss, the absorption at ferromagnetic resonance and the external applied magnetic field required for ferromagnetic resonance. For thin samples the variation of the properties can be explained, at least qualitatively, on the existing theory of ferromagnetic resonance, and the slight semi-conductor nature of ferrites. Thicker samples gave more complicated variations probably due to ‘waveguide effects’ resulting from changes with temperature of the complex dielectric constant and the components of the permeability tensor. The behaviour of these samples with changes of temperature cannot easily be predicted. Some of the useful and interesting properties of ferrite inserts of triangular cross-section are given. Two applications of ferrites are described. The first is an absorption isolator capable of dissipating 50 watts mean power in the reverse direction without the need for forced cooling; this device, using ferrite inserts of triangular cross-section, has very broad-band characteristics. The second is a high-speed waveguide switch. The conditions necessary for rapid switching based on Faraday rotation have been investigated and are included.

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