Coils have different impedance characteristics at various frequencies; typically, at low frequencies, the impedance is small, while it sharply increases at high frequencies. The higher the signal frequency, the more easily the magnetic field radiates. Generally, signal wires are not shielded, such as the CAN bus I am using now, which makes these signal wires perfect antennas. This antenna continuously receives high-frequency signals around it, and the superposition of these signals alters the actual signal to be transmitted. Magnetic rings can effectively pass useful signals while suppressing high-frequency interference signals. In the high-frequency range (greater than 10MHz), inductive reactance remains small, while impedance is large, causing the energy of high-frequency signals to be converted into heat as they pass through magnetic material, thereby hindering the transmission of high-frequency signals and suppressing their interference. The frequency range of suppression is typically related to ferrite suppressor components; usually, the higher the permeability, the lower the suppression frequency. A larger ferrite volume results in better suppression. When the volume is fixed, longer and thinner components have better suppression than shorter and thicker ones, and lower internal resistance results in better suppression.

When suppressing common-mode signal interference, the signal (including the differential signal lines) or the power lines (positive and negative wires) can be simultaneously run through a magnetic ring. To enhance the effect, a few turns can be wound symmetrically around the magnetic ring to increase inductance, thereby enhancing the absorption of common-mode signals. However, this has no effect on differential signals.