EMI/RFI Shielding Types - Mesh Gaskets
Knitted wire mesh can be used as economical gaskets for EMI shielding. Knitted mesh configurations are supplied on spools, coils or cut to length as individual gaskets with or without end seals. Standard profiles for a wide variety of applications are round, round with tail, double round with tail, half round (D) and rectangular.
Most profiles are available as all mesh and all are available with an elastomer core to enhance compression characteristics and increase the deflection range. Standard wire materials are monel, TCS (tin plated copper clad steel) stainless steel and aluminum. Consult the factory for other materials. Wire selection should take into account attenuation potential, mechanical characteristics, and corrosion resistance.
The most commonly used for good conductivity, corrosion resistance and good mechanical characteristics. Not recommended for applications contacting aluminum.
Monel Wire: Per QQ-N-281 - Class A - 0.0045 in. dia.
Tin plated copper clad steel has similar characteristics to Monel, with improved shielding at lower frequencies but slightly lower corrosion resistance.
TCS Wire: ASTM-B-520 - 0.0045 in. dia.
Aluminum wire is normally used only when galvanic compatibility with aluminum housing is required.
Aluminum Wire: AMS 4182 - Alloy 5056, 0.005 in. dia.
Silver/Monel is silver plated nylon filament with a fine strand of Monel wire knitted over a soft elastomer core to provide a very low compression force while achieving excellent attenuation values.
Standard core materials are available in neoprene (sponge and solid), silicone (sponge and solid), and polyurethane foam. Core materials should be selected for temperature, chemical resistance and mechanical characteristics.
Neoprene rubber is an economical, general-purpose elastomer with good compression characteristics. It is available in solid and sponge and in hollow core cross sections.
Sponge: ASTM D6576 Type II Grade A (Formerly MIL-R 6130)
Temperature Range: -31 to 100 C
Solid: MIL-R-6855, Class II, Grade 40
Temperature Range: -40 to 100 C
Silicone rubber is noted for its retention of flexibility, resilience and tensile strength over a wide temperature range. Silicone is more resistant to cleaning solvents than neoprene.
Temperature Range: -75 to 205 C
Solid: A-A-59588 Class II, Grade 40 (Formerly ZZ-R-765)
Temperature Range: -60 to 260 C
Polyurethane Foam should be specified for light compression force applications. This material has good compression set characteristics and is available in rectangular and square solid cross sections.
Temperature Range: -40 to 121 C
Cut to length gaskets are available with sealed ends to capture lose particles produced when the gaskets are cut.
- End Seal: 3M 1357 Adhesive
Dow Corning 3145RTV
Shielding PerformanceMaximum attenuation for all gaskets is achieved as compression force increases. Care must be taken with mesh gaskets to avoid compression set, which will occur when the gasket is compressed beyond 25% of the free height. The use of elastomer cores will extend the operating range. In applications where the gasket is permanently installed between two surfaces, compression set can be tolerated.
EMI Shielding Performance Material H-Field
BeCu >110 dB >110 dB <110 dB Monel 60 dB >115 dB 95 dB TCS 80 dB 125 dB 100 dB Aluminum 38 dB 100 dB 80 dB Silver Monel 60 dB 75 dB 70 dB
Die-castings can be designed for groove mounting to provide good retention and to control the amount of compression.
All profiles except round can be mounted with double-sided pressure sensitive transfer tape for a fast, reliable installation. 3M F9469PC transfer tape may be used at ambient temperatures from -67F to 300F. Apply on clean, oil free surface, and allow a 24-hour cure time for maximum adhesion.
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