Shielding is a method of confining electromagnetic waves to a certain area by making shields such as shells, boxes, and plates from metal. Since the radiation source is divided into a near-area electric field source, a magnetic field source, and a far-area plane wave, the shielding performance of the electromagnetic shielding box is different depending on the radiation source, in terms of material selection, structural shape, and control of leakage of holes.
To achieve the required shielding performance in the design, it is necessary to first determine the radiation source, clarify the frequency range, and then determine the control elements according to the typical leakage structure of each frequency band, and then select the appropriate shielding material and design the shielding shell. The electromagnetic shielding box designed in this way is perfect. With the current increasingly dense electromagnetic spectrum, sharp increase in electromagnetic power density per unit volume, and large-scale mixed use of high and low-level devices or equipment, the electromagnetic environment of equipment and systems is deteriorating, its importance becomes even more prominent.
The shielding effectiveness of the shield depends not only on the material constituting the shield, but also on the structure of the shield. In reality, a completely enclosed shield is of no value. There are many display windows, vents, and gaps for combining different parts on the chassis or shell. Due to the existence of these factors that cause electrical discontinuity, the shielding effectiveness of the shielding body is often very low, or even no shielding effectiveness; therefore, the research on the gaps and holes of the shielding body is also very necessary.
For shielding strong external magnetic fields, the outer layer of the shielding body should be made of materials that are not easily saturated, such as silicon steel; and the inner layer can be made of high-permeability materials that can easily reach saturation, such as permalloy. Conversely, if the strong internal magnetic field is to be shielded, the order of the materials must be over. When installing the inner and outer shields, pay attention to the insulation between each other. When there is no grounding requirement, insulating materials can be used as supports. If grounding is required, non-ferromagnetic materials (such as copper, aluminum) can be used as supports.