Switching power supply generally introduces common mode noise in the frequency range from 10 kHz ~ 50 MHz or even higher. Therefore, to effectively reduce these noises, the common mode inductor shall have a high enough impedance. To achieve this specification, the high permeability Manganese-zinc ferrite and the amorphes material are the most appropriate choices. The Common Inductor's impedance Zs consist of the inductance Xs and the resistance Rs.
Typical specification of standard products:
The following diagram descripts the relationship of Zs, Xs, Rs against the frequency.