The capacitor used in the EMI filter is generally a ceramic capacitor. Due to its physical structure, this ceramic capacitor is also called a feedthrough capacitor.
The core-through capacitor self-inductance is much smaller than the ordinary capacitor, so the self-resonant frequency is very high. At the same time, the through-the-heart design also effectively prevents high frequency signals from being directly coupled from the input to the output. This low-pass, high-impedance combination provides excellent rejection over the 1 GHz frequency range.