Shielding is a method of confining electromagnetic waves within a certain area by a shield made of metal, such as a shell, a box, and a plate. Since the radiation source is divided into near-field electric field source, magnetic field source, and far-field plane wave, the shielding performance of the electromagnetic shielding box is different depending on the radiation source, and is different in material selection, structure shape, and leakage control of the aperture.
In order to achieve the required shielding performance in the design, you must first determine the radiation source, specify 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 to design the shielding shell. This design of the electromagnetic shielding box is perfect. In the current situation where the electromagnetic spectrum is increasingly dense, the electromagnetic power density per unit volume increases sharply, and high-level and low-level devices or equipment are mixed in a large number of factors, resulting in the deterioration of the electromagnetic environment of equipment and systems, its importance becomes even more prominent.
The shielding effectiveness of the shield depends not only on the material making up 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, gaps combined with different parts, etc. on the chassis or housing. Due to these factors that cause electrical discontinuities, the shielding effectiveness of shields is often very low, and there is no shielding effectiveness; therefore, the research on the gaps and holes of shields is also very necessary.
To shield the external strong magnetic field, the outer layer of the shield is made of a material that is not easily saturated, such as silicon steel, and the interior can be made of a highly conductive material that can easily reach saturation, such as Permalloy. On the other hand, if you want to shield the internal strong magnetic field, the order of the materials will come. When installing two shields inside and outside, pay attention to the insulation between them. When there is no grounding requirement, an insulating material can be used as a support. If grounding is required, non-ferromagnetic materials (such as copper and aluminum) can be used as supporting members.
2018-03-29