How does the metal casing of an edge computing box improve its immunity to radiation interference?

The edge computing box uses a metal casing, which provides 20-40dB of shielding effectiveness, significantly improving radiation immunity. The metal casing acts as a Faraday cage, attenuating the electromagnetic field in space, ensuring that the actual field strength experienced by the internal PCB is much lower than the test field strength. For example, if the test field strength is 10V/m, after shielding with a good conductor, the residual field strength inside is <1V/m. Design considerations include that the metal casing must maintain conductivity and continuity; the gap length should be less than 1/20 of the wavelength (for 1GHz, less than 15mm); and conductive springs or conductive cloth pads should be added to the gaps. Etymotic recommends beryllium copper springs with a 50% compression and a contact resistance <10mΩ. Shielded connectors should be used at the interface, overlapping the casing 360°. If the casing is sheet metal with powder coating, the seams need to be ground to ensure conductivity and grounding impedance <5mΩ. Actual testing showed that a plastic-cased edge box crashed at 20V/m; after replacing it with a metal casing, it still worked normally at 40V/m, an improvement of over 6dB. Therefore, for scenarios with high EMC requirements, a metal casing is the preferred choice.