The shielding box plays the role of isolating electromagnetic field interference. Generally, a well-grounded metal mesh or cover is used to achieve electromagnetic shielding, which can not only prevent external electromagnetic field interference, but also prevent the interference of its own electromagnetic field radiation to the outside world. A high-permeability material cover is used to achieve magnetic shielding, which can prevent magnetic field interference.
What are the basic principles that need to be paid attention to when designing the electromagnetic shielding box for the shielding box? The following is introduced by the editor of the manufacturer:
(1) Choose an appropriate shielding effectiveness index. The allocation of overall indicators before electromagnetic shielding design is very important. There are 30 dB and 70 dB criteria: Generally speaking, in a pair of shielding boxes in the same environment, when the difference between the disturbance level and the sensitivity threshold level is less than 30 dB In the design stage, it is not necessary to conduct special shielding design; if the difference between the two is more than 70 dB, it is difficult to ensure compatibility between the two by shielding alone. Even if the target is reached, the equipment cost will increase sharply. Properly adjusted, 30~60 dB is the commonly used expected value for shielding design.
(2) The structure of the shielding body must be concise, reduce unnecessary holes as much as possible, and try not to add extra gaps; avoid opening slender holes, and use circular holes as much as possible for the ventilation holes and discharge them in an array. When there is a conflict between shielding and heat dissipation, open small holes as much as possible, open more holes, and avoid large holes.
(3) There must be no conductors directly passing through the shield. Pay attention to the handling measures of the cable. The handling of the cable is often more important than the shield itself. Once a cable passes through the shielding body, it will significantly deteriorate the shielding effectiveness of the shielding body.
(4) The electrical continuity of the shield is the most important factor affecting the shielding effectiveness. Relatively speaking, the effect of the shielding performance of the material itself is negligible.