The shielding box is a metal body made of various shapes of conductive or magnetic materials, which limits the electromagnetic ability to a certain space, and is used to suppress radiation interference. The better the electrical conductivity and magnetic permeability of the shielding box material, the higher the shielding effectiveness of the shielding box, but the actual metal material cannot take into account these two aspects. For example, copper has good electrical conductivity but poor magnetic permeability; iron has good magnetic permeability, but The conductivity is poor. What material should be used, depending on whether the shielding box mainly relies on reflection loss or absorption loss to determine whether to focus on conductivity or magnetic permeability;
When the frequency is low, the absorption loss is very small, and the reflection loss is the main mechanism of the shielding effectiveness. The reflection loss should be increased as much as possible; the reflection loss is related to the characteristics of the radiation source. For the electric field radiation source, the reflection loss is very large; for the magnetic field radiation source, the reflection loss is very high. small. Therefore, the shielding of magnetic field radiation sources mainly relies on material absorption loss, and materials with higher magnetic permeability should be used as shielding materials.
The reflection loss is related to the distance between the shield and the radiation source. For electric field radiation sources, the closer the distance is, the greater the reflection loss; for magnetic field radiation sources, the closer the distance, the smaller the reflection loss; to correctly judge the nature of the radiation source, determine what it should be Close to the shield, or the principle shield, is an important part of the structural design.
At higher frequencies, absorption loss is the main shielding mechanism, and it has little to do with whether the radiation source is an electric field radiation source or a magnetic field radiation source.
Electric field waves are the easiest to shield, plane waves are second, and magnetic field waves are the most difficult to shield. Especially the low frequency magnetic field (below 1KHz) is difficult to shield. For low-frequency magnetic fields, high-permeability materials should be used, or even a combination of high-conductivity materials and high-permeability materials.
The shielding box controls the test shielding box through the international standard RS-232 interface in accordance with the communication instructions to complete the entire test process. Generally, it is used for small-scale radio frequency modules and large-scale production lines to improve production efficiency.