CHAPTER THREE - Magnetic Materials and Devices

Abstract

This chapter discusses magnetic materials and devices. Inductors, or coils, probably vary more in design than any other component. Superficially they consist merely of wire, wound on an insulator, but in practice they vary from small coils of a few micro-henries operating at many hundreds of megacycles per second, to large inductance coils of a few hundred henries operating in the hundreds of cycles range. To obtain high stability, coils are usually wound on a mechanically stable former, such as ceramic or glass. Apart from single- or multilayer- linear-wound solenoids, other methods of winding are adopted for higher frequency operation such as the “universal” or “progressive universal” in which the wire is oscillated from side to side as the coil is wound to reduce its self-capacitance. If it is required substantially to increase the inductance of a coil without increasing the amount of wire, then it is necessary to insert a ferromagnetic core. This might also provide the facility for the adjustment of inductance.