The principle of electromagnetic shielding

Many people's understanding of electromagnetic shielding is that being covered by a metal box and grounded can achieve the shielding function. In fact, this conclusion is wrong. Because our electromagnetic shielding needs to terminate the interference signal at a shield made of good conductors while ensuring good grounding.
The principle of electromagnetic shielding is that a metal shield interferes with the signal source through reflection or absorption. As the frequency increases, the wavelength becomes equivalent to the size of the holes in the shield, causing leakage from the holes in the shield to become an electromagnetic signal. Shield the most critical control elements.