How can the heat dissipation structure of an electrical power measurement switch (PMS) also provide shielding?

The heat dissipation requirements of PMS (such as ventilation holes and heat sinks) often conflict with shielding requirements, necessitating a clever balance in the design. For ventilation holes, honeycomb metal ventilation plates should be used, with the cutoff frequency of the hexagonal holes designed to be higher than the highest frequency requiring shielding (e.g., 1GHz), typically with a hole diameter <λ/10. If the heat sink is installed externally to the chassis, it should be insulated from the chassis (e.g., through mica gaskets). However, its mounting screws may create leakage paths; feedthrough capacitors can be added to the screws, or non-metallic screws can be used. If the heat sink is internal to the chassis, no special shielding treatment is required, but attention should be paid to its distance from internal circuitry to avoid capacitive coupling. For cases where large openings must be made to install fans, a metal mesh cover can be added to the outside of the fan, with the mesh cover electrically connected to the chassis. All heat dissipation structures that also provide shielding must maintain good electrical connection between their metal parts and the chassis body. After the design is completed, a near-field probe can be used to scan the heat dissipation area to confirm that there is no significant radiation leakage. A well-designed system can ensure that the impact of the heat dissipation structure on the overall shielding effectiveness is less than 3dB.