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Why is the ferrite ring so popular?
Jul 16, 2018

Why is the ferrite ring so popular?

The motherboard, CPU, power supply, and IDE data cable in the computer case work at a very high frequency, so there is a large amount of spatial stray electromagnetic interference signals in the chassis, and the signal strength is also several times to several outside the chassis. Ten times! The USB cable without magnetic ring does not take shielding measures in this space, then these USB cables become good antennas, receiving various messy high-frequency signals in the surrounding environment, and these signals are superimposed on the original transmission. The signal will even change the useful signal originally transmitted, which is prone to problems. At this time, it is necessary to absorb the magnetic ring, and the absorption magnetic ring is also called the ferrite magnetic ring. Then, why can the ferrite magnetic ring inductance suppress the interference signal?

Ferrite is a kind of high-magnetic material that is infiltrated with other metal or magnesium, zinc, nickel and other metals at 2000 °C. In the low frequency range, the ferrite anti-interference core exhibits very low sensitivity. The impedance value does not affect the transmission of useful signals on the data line or signal line. In the high frequency band, starting from about 10MHz, the impedance increases, the inductive component remains small, and the resistive component increases rapidly. When high-frequency energy passes through the magnetic material, the resistive component converts these energies. Dissipated for heat energy consumption. This constitutes a low-pass filter that allows large attenuation of the high-frequency noise signal, while the impedance of the low-frequency useful signal is negligible and does not affect the normal operation of the circuit. Different ferrite suppression elements have different optimal suppression frequency ranges. Generally, the higher the magnetic permeability, the lower the frequency of suppression. In addition, the larger the volume of the ferrite, the better the suppression effect. When the volume is constant, the long and thin shape is better than the short and thick one, and the smaller the inner diameter, the better the suppression effect. However, in the case of DC or AC bias current, there is also a problem of ferrite saturation. The larger the cross-section of the suppression element, the less saturated it is, and the greater the bias current that can be withstood. In order to improve the transmission rate and stability, and to reduce the interference of the transmission line to other devices, such as sound cards, when transmitting data, an electrostatic shielding layer is designed. This shielding layer is made of a thin metal foil or a plurality of thin copper wires woven into a mesh shape, and the surface effect principle of the electrostatic field is applied. That is, the outer surface of the data transmission line is covered with a metal film, and the shielding layer is grounded to the chassis, so that the data line can be well isolated from the spatial interference signal!

In addition, the magnetic rings have different impedance characteristics at different frequencies. The impedance is small at low frequencies, and the impedance of the magnetic ring sharply increases as the signal frequency increases. The higher the signal frequency, the more radiated, and the signal lines are without shielding. These signal lines become good antennas to receive various high-frequency signals in the surrounding environment, and these signals are superimposed on the transmission. The signal will even change the useful signal transmitted, seriously interfere with the normal operation of the electronic device, and reduce the electromagnetic interference (EM) of the electronic device has been considered. Under the action of the magnetic ring, even if the normally useful signal passes smoothly, the high frequency disturbing signal can be well suppressed, and the cost is low. Therefore, ferrite magnetic rings will be so popular.

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