It is a commonly used anti-interference component in electronic circuits, which has a good suppression effect on high-frequency noise. It is generally made of ferrite material (Mn-Zn). The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequencies. As the signal frequency increases, the impedance of the magnetic ring increases sharply. As we all know, the higher the frequency of a signal, the easier it is to radiate out (buying a high-quality computer case also requires reducing electromagnetic leakage). Generally, signal lines do not have a shielding layer, so these signal lines become good antennas to receive various chaotic high-frequency signals in the surrounding environment. These signals are superimposed on the originally transmitted signals, and even change the useful signals that were originally transmitted. So under the action of the magnetic ring, normal and useful signals can pass through well, and high-frequency interference signals can be effectively suppressed, and the cost is low.

Passing the entire cable through a ferrite magnetic ring forms a common mode choke, and the cable can also be wound several turns on top of the magnetic ring as needed. The more turns there are, the better the interference suppression effect on lower frequencies, while the noise suppression effect on higher frequencies is weaker. In practical engineering, the number of turns of the magnetic ring should be adjusted according to the frequency characteristics of the interference current. Usually, when the frequency band of the interference signal is wide, two magnetic rings can be placed on the cable, each with a different number of turns, which can simultaneously suppress high-frequency interference and low-frequency interference. From the mechanism of common mode choke action, the larger its impedance, the more significant the interference suppression effect. The impedance of the common mode choke comes from the common mode inductance Lcm=jwLcm. It is not difficult to see from the formula that for a certain frequency of noise, the larger the inductance of the magnetic ring, the better. But in reality, this is not the case because there are parasitic capacitors on the actual magnetic ring, which exist in parallel with the inductance. When encountering high-frequency interference signals, the capacitive reactance of the capacitor is small, which shortens the inductance of the magnetic ring and causes the common mode choke to lose its function.