What impact does the grounding method of common mode inductance with a metal shell have on its shielding effectiveness?

The grounding method of common-mode inductance with a metal shell directly determines the shielding effect.

Specific impacts include single-point reliable grounding (the shell is connected to the system's safety ground through a low-impedance path): it can quickly conduct the common-mode interference charges induced on the shell to the ground, preventing the shell from becoming a "radiating antenna" and achieving the best shielding effect (typically reducing radiated interference by 20-40dB).

Multi-point grounding: it is prone to forming ground loops, which can lead to potential differences between different grounding points conducting interference through the shell, thereby weakening the shielding effect.

No grounding: the shell will accumulate induced charges, forming an electrostatic field or alternating electromagnetic field, which enhances radiated interference to the outside world, causing shielding failure. It is recommended to adopt "360° full-enclosure grounding" (the shell is connected to the PCB ground plane through multiple vias) to ensure the lowest ground impedance at high frequencies​.