In the electromagnetic field (electromagnetic wave), the surface of the conductor will absorb and lose the energy in the electromagnetic field, causing the electromagnetic field to decay exponentially from the surface of the conductor to the inside (that is, the amplitude of the electric field and the magnetic field decay exponentially). This phenomenon is called the skin effect. The skin effect can prevent high-frequency electromagnetic waves from entering the inside of the conductor, so as to achieve the purpose of electromagnetic shielding, so the electromagnetic shielding cover can be made of metal materials with appropriate thickness. Because the trend current is an eddy current, electromagnetic shielding is also called eddy current shielding.

In order to achieve an effective electromagnetic shielding effect, the shielding thickness of the conductor must be close to the skin depth of the electromagnetic field. The stronger the conductivity of the material, the smaller the skin depth. When the broadcasting frequency is 500 kHz, the skin depth of copper and aluminum are about 0.094 mm and 0.12 mm, respectively, which makes the shielding effect of thinner copper or aluminum sheets better; for higher frequency electromagnetic fields, use Thinner material.

In high frequency electromagnetic fields, ferromagnetic materials are generally not used, because ferromagnetic materials have large hysteresis loss and eddy current loss, which will cause the quality factor (Q value) of the resonant circuit to decrease, so more use high conductivity Electromagnetic shielding of materials.

Since the electromagnetic shielding of copper and aluminum is no longer suitable for electromagnetic shielding of copper, aluminum, etc., if Fe is used to make the shield, the electromagnetic field in iron attenuates much faster than copper and aluminum, so only thinner iron sheets are needed. NS. In fact, this time has become a magnetostatic shield.

Electromagnetic shielding and electrostatic shielding have something in common, that is, the shielding cover is made of highly conductive metal. The difference is that electrostatic shielding can only eliminate capacitive coupling and prevent the influence of electrostatic induction, and the shield must be grounded; electromagnetic shielding uses eddy current to prevent electromagnetic field penetration and eliminate electromagnetic field interference. The shield does not need to be grounded. However, since the electromagnetic shielding shield increases the electrostatic coupling, in order to avoid this adverse effect, the shielding case should still be grounded. In this case, the electromagnetic shielding also plays a role of electrostatic shielding.

It can be seen that conductive cloth has advantages in electromagnetic shielding. The conductive cloth is generally plated on the chemical fiber cloth base by a very thin copper and nickel metal layer. Therefore, the conductive cloth has strong electromagnetic shielding properties, but also has thinness and flexibility, and can be attached to other materials.