The quality of the shielding box is actually inseparable from the effect of the shielding box. As far as we know, the shielding effect is evaluated by the multiple of the shielding attenuation of the field strength. In a linear circuit, the shielding effect is equal to the ratio of the voltage in the circuit caused by the field before and after shielding, generally measured in decibels. According to the principles of physics, shielding is divided into electrical shielding, magnetic shielding and electromagnetic shielding, and specific shielding is often used concurrently.
Electronic equipment shielding and grounding are used to attenuate constant or low frequency (such as 50 Hz) magnetic field shields. If the box or shell made of magnetic conductive material is placed in the magnetic field, the magnetic field inside the box will be weakened; on the contrary, if the magnetic field is inside the box, the magnetic field outside the box will be weakened. In order to improve the magnetic shielding effect, it is necessary to use high permeability materials to make the shield, increase the wall thickness and reduce the volume of the box, but when there are magnetic elements in the box, the box wall and the magnetic elements must be kept at a certain distance. The gap structure between the box and the lid should achieve low magnetic resistance for magnetic flux.
Electronic equipment shielding and grounding are shields used to attenuate electromagnetic waves. When the electromagnetic wave is directed to the metal plate, the metal has a strong ability to reflect and absorb the attenuated electromagnetic wave, and the wave passing through the metal plate is far weaker than the incident wave. The higher the frequency of the electromagnetic wave, the greater the thickness of the plate, and the better the conductive and magnetic properties of the metal, the greater the attenuation of the plate to the wave. To improve the electromagnetic shielding effect is to avoid the pores of the shield and reduce the contact resistance of the seam.
Then through these characteristics, we can conclude that the measures to improve the shielding effect are as follows: (1) Increase the shielding of S to B. Therefore, the shielding effect of the box and the shell is better than that of the board, and the board is better than the grid and net; ②Improve the conductivity of the shielding surface; ③Reduce the ground impedance and shorten the ground wire as much as possible; In the high frequency, the shield is directly more Point grounding (because it contains inductive components); ④Reduce the contact resistance and add a conductive elastic pad between the shielding box and the cover.
Now everyone knows why the quality of the shielding box is closely related to the effect of the shielding box! If you have any questions, please feel free to discuss and learn.