This section provides overview, applications, and principles of ferrites. Also, please take a look at the list of 4 ferrite manufacturers and their company rankings.
Ferrite is a ceramic composed mainly of iron oxide and is used as a magnetic material.
Because it is ceramic, its electrical resistance is higher than that of metallic magnetic materials and is characterized by excellent corrosion and chemical resistance.
Ferrites are mainly used as a magnet called ferrites magnet. Because it is inexpensive and can be mass-produced, its use fields are diverse, including home appliances, game consoles, and personal computers.
Ferrites are also used as the core of transformers and as a material to block electromagnetic waves in radio wave anechoic boxes and anechoic chambers. Ferrites particles are also used as carriers to carry toner in laser printers, etc. Ferrites are a magnetic material that permeates our daily lives.
There are three types of ferrites as follows.
Spinel-type ferrites are ferrites whose main component is Fe2O4. In the past (because its main component was iron oxide) it had to be heat-treated at a temperature of 800°C or higher to be produced.
In recent years, it has become possible to produce it at temperatures as low as 100°C by conducting the reaction in an alkaline solution. Spinel-type ferrites exhibits soft magnetic properties when mixed with additives such as manganese, cobalt, nickel, copper, and zinc.
Hexagonal ferrites are ferrites with the chemical formula M-Fe12O19 (M: Ba, Sr, Pb, etc.). It is hard ferrites that exhibits complex magnetism when barium or strontium is added.
Garnet-type ferrites are ferrites with the same type of crystal structure as natural pomegranate stone and has the chemical formula Mg3Al2Si3O12. Garnet-type ferrites are soft ferrites that exhibits the same mild magnetic properties as spinel-type ferrites.
Ferrites are also used as a noise-reducing component. For example, EMI (Electromagnetic Interface) is a significant problem in high-speed communication signals such as USB, etc. EMI (Electromagnetic Interference) is not limited to communication lines but refers to unwanted electromagnetic noise emitted by electrical equipment.
In terms of EMI certification and quality assurance, electrical equipment is classified as Class A or Class B, and appropriate EMI countermeasures are required for each product. Usually, EMI countermeasures are taken at the time of circuit and pattern design, but ferrites may be used in the later stages of design and when development time is limited.
By wrapping the ferrites around the noise-generating harness, the impedance of the cable changes according to the magnetization of the ferrites, and as a result, the noise current can be reduced. However, reducing noise current means that high-frequency components are reduced. In other words, the ferrites functions as a simple low-pass filter.
Thus, it is essential to keep in mind that reducing high-frequency components leads to signal distortion, which may cause waveform accentuation and, eventually, signal quality degradation. The noise reduction characteristics of ferrites are determined by its impedance, which varies depending on the ferrites material, size, and number of turns.
When the ferrites material is the same and the exact size is used, the impedance generally increases with the number of turns N in the harness. Although the increase in impedance results in more powerful noise suppression, the number of turns should be selected according to the frequency band to be suppressed.
The cross-sectional area also affects the impedance, and as a rule, ferrites with a smaller inner diameter and a larger outer diameter has a higher impedance. A wide range of ferrites are available as high-frequency countermeasure components. It is important to understand the characteristics of each and use ferrites with the appropriate characteristics for the frequency band to be counteracted.
*Including some distributors, etc.
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