Engineers often use ferrite components in electronic circuits. These ferrite components are nonconductive, ceramic compound materials made with numerous combinations of iron oxides. Electronic components typically use them because of their high electrical resistivity and low eddy current losses. Ferrites can have various properties depending on their condition of synthesis, sintering temperature, composition, and grain size.
Manufacturers classify ferrites based on their crystal structure and magnetic properties. In general, they are of two types—soft and hard. Soft ferrites, made from magnesium, manganese, nickel, cobalt, and zinc, have low coercivity, such that their magnetism changes easily, and they act as conductors of magnetic fields. On the other hand, hard ferrites make very good permanent magnets, owing to their high coercivity.
It is also possible to classify ferrites based on their crystal structure. Typically, there are four groups— spinel, garnet, ortho, and hexagonal. Manufacturers distinguish them based on the molar ratio of ferric oxide to other oxide compounds present in the ferrite ceramic.
Crystallizing spinel ferrite results in a cubic structure with oxygen anions in a closely packed arrangement. Here, a unit cell comprises 32 oxygen ions. The anions form an FCC or face-centered cubic array.
Ferrites typically exhibit a permanent type of magnetism that physicists refer to as ferrimagnetism. This is a phenomenon that aligns the magnetic moments of atoms in both antiparallel and parallel directions. This alignment partially cancels the magnetic field, making the overall magnetic field of a ferrite material weaker than that of ferromagnetic materials.
Various types of ferrites are available. In electronic circuits, engineers typically use them as beads. For a ferrite bead, the resistivity is the strongest in a thin frequency band. This feature makes ferrite beads very useful as frequency-dependant resistors. Above the frequency band, the impedance of the bead begins to appear capacitative.
Other types of ferrites structures are also available for use in electronics. For instance, there are flat ferrites, typically rectangular or disc-shaped. Engineers use them in applications where they need a flat shape, such as power inductors, planar transformers, filters, and power inductors. Flat ferrites are very useful for suppressing radio frequency interference and electromagnetic emissions.
Ferrite rings and sleeves are also available. These are cylindrical-shaped components, suitable for placing around a wire or cable. It acts like a filter that can block high-frequency noise, allowing only low-frequency signals to pass through the wire or cable. Manufacturers choose the inner diameter of the ferrite to closely match the outer diameter of the cable, as this maximizes the benefits of interference suppression. Ferrite rings and sleeves are very useful in applications like data communications, consumer electronics, and power supplies to improve signal integrity and reduce interference effects on circuit performance.
Multi-hole ferrite beads are cylindrical cores with typically 6 through-holes running along the axis of the cylinder. When a trace or wire in a circuit is wound through its holes, the multi-hole ferrite bead behaves as a low-pass filter. It blocks unwanted high-frequency interference signals and allows only low-frequency signals to pass through the wire.