How much does the size of the heat dissipation holes on an edge computing box affect its shielding effectiveness?

Improperly designed heat dissipation holes in the metal casing of edge computing boxes will severely degrade shielding effectiveness. When the hole length is greater than λ/20, electromagnetic leakage is significant. For example, at 1 GHz, λ = 300 mm, and λ/20 = 15 mm, if the hole diameter is 8 mm or the long slot is 15 mm, the shielding effectiveness drops to below 10 dB. Improvement methods:

1. Use a small round hole array with a hole diameter < 3 mm and a spacing < 5 mm, achieving a shielding effectiveness > 40 dB.

2. Use a hexagonal honeycomb ventilation board with a waveguide cutoff frequency far lower than the interference frequency, a hole depth > 5 mm, and a hole side length < 3 mm, achieving a shielding effectiveness > 60 dB.

3. Add conductive wire mesh pads to the holes to balance heat dissipation and grounding. If the hole cannot be changed, conductive foam can be applied to the inside of the hole to partially cover the area, but not completely block it.

Actual measurements show that changing an 8 mm round hole to a 3 mm × 3 mm square hole array reduces the radiated emission of the edge box at 1 GHz by 14 dB.