Kemtron explains the advantages of honeycomb vents
Most electronic enclosures need some form of air ventilation to keep cool the electronics within. If this is a RFI/EMI shielded enclosure then the overall shielding effectiveness of the enclosure can be compromised. For many commercial applications perforated sheet, metal or metallised plastic will suffice but for high performance requirements waveguides provide superior shielding over a wide frequency range.
Waveguides can be circular, rectangular or honeycomb shaped. The principle is that of “Waveguide beyond cutoff”. The honeycomb vent is series of tubes that acts as a waveguide, guiding electromagnetic waves into or out of the enclosure, but as the tubes are long enough then it attenuates those waves. Typically the tube should be at least 3 times as long as the diameter. Good practice is 4 times. Therefore a 3.18mm cell should be 12.7mm long.
The most cost effective is aluminium honeycomb because it offers high shielding performance, light weight and good airflow as it is 96% open area. A typical shielded enclosure will use two honeycomb ventilation panels one as the inlet and one for the exhaust.
Aluminium honeycomb vents are supplied in an aluminium frame with an EMI gasket to ensure a good electrically conductive bond with the enclosure. Many frame styles are available to suit different mounting methods.
Kemtron’s standard honeycomb vent uses two layers of 3.18mm cell x 6.4mm thick laid at 90°, and is known as cross cell. It improves shielding performance by eliminating any polarizing effects.
Kemtron’s standard finish (Kempass) for aluminium vent panels fully meets the RoHS directive and applies permanganate passivation which is a chromate free, inorganic and non toxic coating. The process produces a dense, uniform coating consisting of aluminium and reduced manganese oxides giving a light yellow colour to the surface. The surface finish is conductive with a low contact resistance. It also meets all requirements of MIL-C-5541E for corrosion and electrical conductivity. Surtec 650, tin or nickel plating finishes are also available. A range of painted finishes to match enclosure finishes or military colours is also offered. Protective kick plates can be incorporated in the vent to prevent damage to the honeycomb.
Other vents available are commercial grade standard size fan vents, steel, stainless steel and brass to special order.
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