Electromagnetic shielding is the isolation of metal between two spatial areas to control the induction and radiation of electric fields, magnetic fields and electromagnetic waves from one area to another.
Specifically, shielding is used to surround the interference sources of components, circuits, assemblies, cables or the entire system to prevent the interference electromagnetic field from spreading; to surround the receiving circuit, equipment or system to prevent them from being exposed to the external electromagnetic field. influences.
Because the shielding box plays a role in absorbing energy (eddy current loss), reflected energy (reflection of electromagnetic waves on the interface of the shielding box) and offsetting energy (electrical interference) from external interference electromagnetic waves and internal electromagnetic waves from wires, cables, components, circuits or systems, etc. Magnetic induction produces a reverse electromagnetic field on the shielding layer, which can offset part of the effect of interfering electromagnetic waves), so the shielding box has the function of reducing interference.
1. When the frequency of the interfering electromagnetic field is high, the eddy current generated in the metal material with low resistivity is used to form the cancellation effect of the external electromagnetic wave, so as to achieve the shielding effect.
2. When the frequency of the interference electromagnetic wave is low, materials with high magnetic permeability should be used, so that the lines of magnetic force are limited to the inside of the shielding body and prevent spreading to the shielded space.
3. In some occasions, if a good shielding effect is required for both high-frequency and low-frequency electromagnetic fields, different metal materials are often used to form a multi-layer shielding body.
4. Many people do not understand the principle of electromagnetic shielding. They think that as long as a box is made of metal and then the box is grounded, electromagnetic shielding can be achieved. This is a wrong understanding.