how to design the right emi gasket
Jan van Tienhoven
Specialist in Electro Magnetic Compatibilty solutions and materials
Rules of thumb for gasket choice, DEPENDING ON THE TYPE OF ENCLOSURE
41?Very small construction, (smaller than 150 x 150) grooves, casted, molded or machined: conductive profiles, o-ring or cut gasket out of highly conductive rubber are suitable (fig. 41.1).
Figure 41.1: Groove construction with conductive o-ring gasket
42?Small construction, (about 200 x 200mm) multi-shield gasket, consisting of metal wire from top to bottom through a soft silicone rubber with a thickness of 2-3 mm are suitable. (fig. 42.1).
Figure 42.1: Examples of gasket solutions for small constructions
43?Medium size construction, zinc-plated steel/metal: standard shield, neoprene foam with water seal, minimum width about 4mm and thickness 2-3 mm. (fig. 43.1).
Figure 43.1: Examples of gasket solutions for medium size constructions
44?Full-size rack with a door. Ultra-soft twin shield with separate water seal or knitted mesh over silicone tube with water seal, V-shape with additional water sealing, thickness 6-10 mm is suitable. Other products like finger strips, textile-covered parts, clip-on gaskets or custom build hybrid gaskets are suitable. (fig. 44.1).
Figure 44.1: Examples of gasket solutions for larger constructions like server racks
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Shielded Doors
45?The closing force of a shielded door/Faraday cage door should be reduced as much as possible so that it can be opened by hands. For more information read?55
Figure 45.1: Construction of a shielded door
46?Gasket thickness
Ultra-soft gaskets will help limit the closing force as well as bending of the door. (fig. 29.1).
47?Just as indication, at a server cabinet of 600 x 2500mm, a gasket of 6mm thick may be used and an electronics housing 200x600mm a gasket of 6 x 4mm is an optimal size. All our gaskets can also be provided with water sealing.?In order for a gasket to have?sufficient stability, its width should exceed its height.
48?In the case of a?screwed connection?at a housing, entry panels, windows, or vent panels, the closing force is less important. Depending on the plate thickness and bolt distance, 1-2mm is common and Amucor shield is a very good choice for the materials used most often.
49?When the housing has only?one edge flange?while a water and EMI seal are needed, this can be created by using clip-on gaskets. Of these gaskets, more than 200 different shapes have been produced edged with mesh or highly conductive textiles. They are mounted by means of clamping. When we cut them into shape according to the customer’s wishes, they can even make angles of 90 degrees.
Figure 49.1: Example of a clip-on gasket construction
50?For instruments and introducing?high currents?into a construction we make over 2400 different Be-Cu finger strips. These are not allowed in every country and are susceptible to being damaged when they are used in a construction that is not protected properly (knife-edge).