Shielding Is Meant to Establish Metal Isolation Between Two Spatial Regions to Control the Induction And Radiation Of Electric Field, Magnetic Field And Electromagnetic Wave From One Region to the Other. to Be Specific, It Is to Use A Shielding Enclosure to Enclose the Interference Source Of the Component, Circuit, Assembly, Cable Or the Whole System to Prevent the Outward Diffusion Of the Interfering Electromagnetic Field, Or to Enclose the Receiving Circuit, Device, Or System to Protect It From Any External Electromagnetic Field. the Shielding Enclosure Can Reduce the Interference As It Can Absorb (eddy-current Loss), Reflect (reflection Of the Electromagnetic Waves on the Shield Enclosure), And Offset (electromagnetic Induction Can Produce A Reverse Electromagnetic Field on the Shielding Layer Which Can Offset Part Of the Interfering Electromagnetic Waves) the Energies Of the Interfering Electromagnetic Waves From Both Outside And Inside Of the Wires, Cables, Components, Circuits Or Systems. 
(1) Where the Interfering Electromagnetic Field Has A Higher Frequency, the Eddy Currents Generated in the Metal Materials With Low Resistivity Can Be Used to Offset the External Electromagnetic Waves, Achieving the Shielding Effects.
(2) Where the Interfering Electromagnetic Waves Have A Lower Frequency, Materials With High Magnetic Permeability Should Be Used to Limit the Lines Of Magnetic Force Within the Interior Of the Shielding Enclosure, Preventing Them From Diffusing to the Shielded Space.
(3) in Some Cases, If Good Shielding Effects Against Both High Frequency And Low Frequency Electromagnetic Fields Are Required, Different Metal Materials Are Often Used to Form A Multilayer Shielding Enclosure.