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What is a Ferrite Inductor?

Rodney A. Crater

Last Modified Date: February 05, 2024

A ferrite inductor is an electrical or electronic component made from ferrite magnetic material and typically, but not always, a coiled electrically conducting pathway. It is used to passively limit, modify, or enhance electrical, electromagnetic (EM), or radio frequency (RF) energy. Inductors made of ferrite are often utilized in situations that require suppression of electromagnetic interference (EMI) or radio frequency interference (RFI). They are also used as RF transformers, ferrite core inductors, ferrite bead inductors, in switched-mode power supplies (SMPS), and for chokes on electrical power cords used for electronic devices such as computers.

When electrical current passes through an electric wire, or conductor, a magnetic field around the wire called flux is created. If the conductor is looped, or coiled, the flux field is enhanced and can store a larger amount of EM energy while current continues to flow. A wire which is coiled in this manner is called an inductor. As current flow stops flowing through an inductor, the energy stored as flux outside the coil is reabsorbed by the wire and converted back into electrical current. This induced current then flows in the same direction as the original current until the energy stored in the EM field of the inductor is exhausted.

Ferrite is an electrically non-conductive, magnetic material made from ceramic, ferromagnetic, and ferrimagnetic substances. When a piece of ferrite material is used as core material for a ferrite inductor or placed around an inductor, the EM storage of the flux field may be greatly enhanced. Depending on what materials are used to create them, different types of ferrites have special EM characteristics in relation to the properties of coercivity, resistivity, remanence, and magnetic permeability. These characteristics determine the affect needed when selecting a suitable ferrite inductor for a specific application.

Alternating current (AC) causes electricity to flow back and forth in a wire, cycling at a certain rate called frequency. When the direction of current flow changes in a wire, the flux energy stored in a ferrite inductor will impose a current that flows against the new current. This has the effect of canceling out alternating current altogether because each time the current changes direction, a new flux field is created that cancels out the next opposing change in direction. Ferrite inductors can be selected and tuned to eliminate particular sets of AC frequencies. In this way, a ferrite inductor can eliminate current in a wire caused by EMI and RFI.

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Discussion Comments

MrMoody

December 26, 2011

@miriam98 - I think that the simplest example of induction is a basic magnet. As you recall from your high school science class, all you need to do to create a simple magnet is wrap magnetic wire around a conductive metal element. The result will be a magnetic field, albeit a slight one.

I think that the more wiring that you wrap around the metal the greater the field will be. I think that field is what the article would classify as a flux. You can use that homemade magnet to pick up things like paper clips, using its stored energy.

miriam98

December 25, 2011

This is a good introduction to the subject. Given how the ferrite inductors work, I think that they have usefulness in audio applications as well.

For example, I’ve read that a way to eliminate some of the familiar buzz or hum when using microphones is to use coiled wires. I suppose that these are inductors, which use their magnetic shield, as it were, to eliminate outside interference.

I don’t know what kinds of cables do this best; perhaps they are the XLR kind or something like that. I just have regular cables that fit into the microphone jack and my guess is that’s why I get a hum sometimes.