The compounds used in the composition of ferrites can be compared to the more familiar compounds
used in transistors. As in the construction of transistors, a wide range of magnetic and electrical properties
can be produced by the proper choice of atoms in the right proportions. An example of a ferrite device is
shown in figure 1-72.
Figure 1-72.Ferrite attenuator.
Ferrites have long been used at conventional frequencies in computers, television, and magnetic
recording systems. The use of ferrites at microwave frequencies is a relatively new development and has
had considerable influence on the design of microwave systems. In the past, the microwave equipment
was made to conform to the frequency of the system and the design possibilities were limited. The unique
properties of ferrites provide a variable reactance by which microwave energy can be manipulated to
conform to the microwave system. At present, ferrites are used as LOAD ISOLATORS, PHASE
SHIFTERS, VARIABLE ATTENUATORS, MODULATORS, and SWITCHES in microwave systems.
The operation of ferrites as isolators, attenuators, and phase shifters will be explained in the following
paragraphs. The operation of ferrites in other applications will be explained in later NEETS modules.
Ferromagnetism is a continuation of the conventional domain theory of magnetism that was explained in
NEETS, Module 1, Matter, Energy, and Direct Current. A review of the section on magnetism might be
helpful to you at this point.
The magnetic property of any material is a result of electron movement within the atoms of the
material. Electrons have two basic types of motion. The most familiar is the ORBITAL movement of the
electron about the nucleus of the atom. Less familiar, but even more important, is the movement of the
electron about its own axis, called ELECTRON SPIN.
You will recall that magnetic fields are generated by current flow. Since current is the movement of
electrons, the movement of the electrons within an atom create magnetic fields. The magnetic fields
caused by the movement of the electrons about the nucleus have little effect on the magnetic properties of
a material. The magnetic fields caused by electron spin combine to give a material magnetic properties.
The different types of electron movement are illustrated in figure 1-73. In most materials the spin axes of
the electrons are so randomly arranged that the magnetic fields largely cancel out and the material
displays no significant magnetic properties. The electron spin axes within some materials, such as iron
and nickel, can be caused to align by applying an external magnetic field. The alignment of the electrons
within a material causes the magnetic fields to add, and the material then has magnetic properties.