In electronic equipment, electromagnetic interference energy is generally transmitted through conductive coupling and radiative coupling. When designing, the conductive coupling is usually suppressed by filtering methods; while the radiating coupling is controlled by electromagnetic shielding measures.
Electromagnetic shielding is one of the important means to solve the electromagnetic compatibility problem of electronic equipment. Most of the electromagnetic compatibility problems can be solved by electromagnetic shielding. Especially with the increasing frequency of circuit operation, the circuit board design alone cannot meet the electromagnetic compatibility standards. Requirements. There are many differences between the shielding design of electrical equipment and the traditional structural design. Generally, if the shielding problem is not considered in the structural design, it is difficult to meet the electromagnetic compatibility requirements. Therefore, when designing electronic products, electromagnetic shielding must be considered from the very beginning.
Electromagnetic shielding is mainly used to prevent the influence of high-frequency electromagnetic fields, so as to effectively control the radiation and propagation of electromagnetic waves from one area to another. The basic principle is to use low-resistance conductor materials to produce a shielding effect by the reflection of electromagnetic waves on the surface of the shielding body, the absorption inside the conductor and the loss during transmission.
The purpose of electromagnetic shielding is to suppress the propagation of electromagnetic noise, so that the instrument in an electromagnetic environment avoids electromagnetic interference (EMI) and does not produce electromagnetic interference. Usually, materials with good conductivity and magnetic permeability are used to shield the equipment. The area is separated from the outside by meters.
The effectiveness of the shielding body is measured by the shielding effectiveness. The shielding effectiveness is defined as the ratio of the electromagnetic field strength E1 when there is no shield in the same place in the electromagnetic field to the electromagnetic field strength E2 when there is shielding, which characterizes the shielding body's electromagnetic wave The degree of attenuation. Shielded rooms used for electromagnetic compatibility purposes can usually attenuate the intensity of electromagnetic waves to one percent to one millionth of the original, so the shielding effectiveness is usually expressed in decibels.