Most EMI failures don’t occur because an enclosure isn’t shielded; they happen because the shield isn’t continuous. Even a one-millimeter seam between panels can act as a slot antenna, leaking radiation strong enough to fail MIL-STD-461 or FCC Part 15 compliance. The gasket is what closes that circuit. It converts mechanical contact into electrical continuity, ensuring that the enclosure functions as a single conductive shell.

Choosing the right gasket means balancing three variables: shielding effectiveness, compression mechanics, and material compatibility. Get anyone wrong, and attenuation drops fast. A nickel-graphite elastomer that performs at 110 dB in lab conditions can lose half that effectiveness if under-compressed or paired with an anodized aluminum flange. Selecting the right material and geometry from the start prevents redesigns, compliance retests, and field failures later.

What Do EMI Gaskets Do?

EMI gaskets prevent electromagnetic interference (EMI) by creating a conductive, sealed barrier over openings in electronic device enclosures, such as doors, seams, or fastener lines.

Made from electrically conductive materials such as metal, wire mesh, or conductive elastomers, these gaskets are designed to reflect or absorb interfering signals, protecting sensitive internal components from malfunction.

How They Work

• Shielding Principle:EMI gaskets create a continuous, electrically conductive shield around sensitive components, similar in concept to a Faraday cage.
• Signal Interception:When electromagnetic signals encounter the gasket, they are either reflected away or absorbed and dissipated as heat through the conductive material.
• Conduit for Protection:By sealing gaps and seams in electronic enclosures, the gaskets prevent unwanted RF coupling, ensuring the internal circuitry operates within defined electromagnetic limits.

Design Considerations

Effective gasket performance depends on more than just material choice; it’s a function of mechanical compression, surface conductivity, and environmental compatibility. These variables must be engineered together to achieve consistent attenuation across the operating bandwidth.

• Compression Force:A typical conductive elastomer requires 15–25% compression for optimal contact resistance (<10 mΩ). Insufficient compression creates discontinuities; excessive compression leads to permanent deformation or loss of elasticity. Finite element analysis (FEA) can help determine uniform contact pressure across irregular flanges.
• Environmental Factors: Real-world operation defines material life. Outdoor telecom housings, for instance, require UV- and ozone-resistant fluorosilicone gaskets that maintain conductivity after exposure to salt fog for over 1,000 hours (per MIL-STD-810). In contrast, medical or aerospace applications may prioritize low outgassing and sterilization resistance over weathering stability.
• Material Compatibility:When conductive fillers (like silver-aluminum) contact dissimilar metals, galvanic corrosion can erode performance. Using similar metals or adding a conductive surface treatment prevents oxidation and preserves conductivity over time.

Materials and Profiles

The right gasket starts with the right material system and how it interfaces mechanically. Electrical performance is measured in decibels (dB) of shielding effectiveness; however, actual results depend on factors such as compression, surface finish, and continuity. JEMIC offers material classes engineered for specific use cases.

• Conductive Elastomers:Silicone or fluorosilicone matrices filled with silver-nickel or nickel-graphite for broadband shielding up to 120 dB. Common in enclosures requiring both EMI and environmental sealing (IP65–IP68).
• Metal-Impregnated Foams and Fabrics:Polyurethane cores wrapped in conductive textiles for 60–90 dB attenuation at minimal closure force, which is ideal for rackmount systems and access panels.
• Wire-Oriented Silicones and Knitted Wire Mesh:Hybrid structures providing anisotropic conductivity and superior durability under vibration. Typical in military avionics and radar assemblies operating up to 18 GHz.

Every profile—O-ring, D-shape, or custom extrusion—is engineered to meet defined compression targets and mounting tolerances. For instance, a 3.2 mm nickel-graphite O-ring may yield 100 dB attenuation at 10 GHz when compressed 20%.

The Right Gasket Makes the Shield

Shielding success isn’t achieved by filling a gap; it’s achieved by controlling how current flows across it. The right EMI gasket converts mechanical contact into electrical certainty, turning exposed seams into part of the enclosure’s conductive shell. Work with JEMIC’s engineers to define measurable targets, such as attenuation in dB, contact resistance in mΩ, and compression in N/mm, and design a gasket that performs predictably, lot after lot.

Because in EMI control, continuity isn’t optional, it’s engineered.

Related Reading

• When Does a Form-in-Place (FIP) EMI Gasket Actually Outperform a Fabric-over-Foam Gasket?
  For design engineers managing electromagnetic interference (EMI) requirements, one critical decision is determining which gasket type best suits their application: Form-in-Place (FIP) EMI gaskets or traditional Fabric-over-Foam (FoF) gaskets.
• Why is it Important to Test EMI Gaskets?
• Why EMI Gaskets & Shielding are More Critical Than Ever in Today’s Connected World