A Review on Ferrite Devices

ABSTRACT

Ferrites are essentially a class of semiconductors showing ferromagnetic properties. Their high resistivity combined with high permeabilities make them useful for a variety of applications practically covering every field in electronics and communications. A brief review of the principles of ferromagnetism in ferrites is given. The tensor nature of r.f. permeability for linear polarization and the scalar permeability for circular polarization are explained with reference to their applications in microwave techniques. Ferrites generally exhibit a variety of non-reciprocal properties in the microwave region which form the basis of their applications in this region. Some of the ferrite devices in the microwave region are circulators, isolators and differential phase shifters. Devices have been developed for both circular and rectangular waveguide configurations based on any one of the non-reciprocal properties.

Ferrites with rectangular BH loops are employed in a variety of ways in computer circuits. These include circular cores for switching circuits, random access memories, ferroplates, transfluxors, etc. Ferrites are also employed in a large number of other applications ranging from communication networks to components in radio and television circuits. Hard ferrites with barium oxide compositions are used in compact permanent magnets with flux densities in the range 1500–2000 gauss. Piezomagnetic ferrites are employed in ultrasonics.

A brief survey of all the above applications have been made in this article.