< p > electromagnetic compatibility EMC (ElectromagneticCompatibility) abbreviation, is refers to an electronic equipment is neither interfere with other equipment, at the same time, it is not affected by other equipment. Electromagnetic compatibility, like the safety we are familiar with, is one of the most important indicators of product quality. Safety concerns people and property, while electromagnetic compatibility concerns people and the environment.

< p > electronic components to the outside world, known as the EMI (ElectromagneticInterference); Electromagnetic waves and electronic components, produced by interference phenomenon, called the EMS (ElectromagneticSusceptibility). For example, the common "snowflake" on the TV screen indicates that the received signal is interfered with.

Because the shield plays a role in absorbing energy (eddy current loss), reflecting energy (reflection of electromagnetic waves on the interface of electromagnetic waves on the shield) and cancelling energy (electromagnetic induction generates a reverse electromagnetic field on the shield layer, which can cancel part of the interference electromagnetic waves) for external interference electromagnetic waves and internal electromagnetic waves from wires, cables, components, circuits or systems. Therefore, the shield has the function of reducing interference.

(1) When the frequency of interference electromagnetic field is high, the eddy current generated in the metal material with low resistivity is used to form a counteracting effect on the external electromagnetic wave, so as to achieve the shielding effect.

(2) When the frequency of interference electromagnetic waves is low, materials with high magnetic permeability should be used, so that the magnetic field line is limited to the inside of the shield to prevent diffusion to the shielded space.

(3) In some cases, if it is required to have a good shielding effect on high and low frequency electromagnetic fields, different metal materials are often used to form multi-layer shields.