When Protection Starts to Slip
Every engineer and product manager who works with EMI shielding has faced the same frustrating moment: the system that passed compliance testing months ago suddenly fails in the field. Radios hiss, displays glitch, signals degrade—and the culprit is often traced back to an EMI gasket that no longer performs as designed. The device itself hasn’t changed, but the shield has quietly weakened.
This problem isn’t just a nuisance; it can threaten safety, compliance, and credibility. From the electronics in naval platforms to the life-saving reliability of medical devices, the degradation of EMI gaskets can carry heavy costs. A study published in the Journal of Liberal Arts and Humanities on electromagnetic interference (EMI) and electromagnetic compatibility (EMC) helps explain why shielding fails, how physical and environmental factors accelerate that failure, and what design choices extend gasket life.
Compression Set: The Silent Saboteur
One of the primary reasons EMI gaskets lose effectiveness is due to compression set. Over time, the constant squeezing of a gasket against a metal seam flattens the material. Once that elasticity is lost, the gasket no longer fills the gap, and tiny leak paths appear.
- These microscopic leaks let electromagnetic fields slip through, especially at the seams of enclosures.
- As noted in the scholarly text, even small discontinuities in bonding or grounding routes create openings for interference.
- Once EMI has a path, it reflects, couples, and amplifies instead of being absorbed.
In practice, that means a system that looked sealed on paper begins radiating noise or, worse, starts picking it up.
When Metals Clash: Galvanic Corrosion
It isn’t always mechanical stress that kills a gasket. In many cases, it’s chemistry. When two dissimilar metals are paired—say, an aluminum enclosure with a silver-filled elastomer—galvanic corrosion can quietly erode the conductive path. Moisture, salt, and even air pollution accelerate the breakdown.
Think of it this way: the gasket is designed to be conductive, but corrosion builds a thin insulating barrier. That barrier doesn’t just increase resistance; it flips the gasket from being a shield into a potential source of noise. The PDF emphasizes how bonding and grounding degrade over time when junctions are exposed to the elements.
The Heat Factor: Expansion, Contraction, and Stress
Thermal cycling is another overlooked destroyer of shielding. Devices in aerospace, automotive, or marine environments expand and contract daily with heat. A gasket compressed tightly in the lab may loosen after hundreds of cycles in the field.
If your EMI gasket is expected to perform in environments with wide temperature swings, you can’t ignore thermal stress. Elastomers and foams fatigue differently; choosing the wrong material guarantees early failure.
Did You Choose the Right Material?
Selecting the wrong gasket material is a mistake that often shows up only after deployment.
- Fabric-over-foam gaskets work well for lightweight consumer devices but may suffer under repeated compression.
- Conductive elastomers offer durability in harsh environments but cost more up front.
- Wire-oriented silicone provides both resilience and conductivity, especially in high-frequency shielding applications.
The academic text underscores that shielding effectiveness is a balance of reflection, absorption, and bonding integrity. That balance only holds if the gasket material matches the operating environment.
Testing Isn’t a One-and-Done
Passing initial EMC testing doesn’t mean you’re safe forever. Gasket performance degrades under stress, and standards like FCC Part 15 or MIL-STD-461 don’t account for years of use. Vessels and aircraft undergo repairs, replacements, and modifications that slowly erode EMC compliance.
In other words, today’s pass is tomorrow’s failure if you’re not monitoring. Periodic inspection and re-testing, especially around high-risk junctions, keep small problems from escalating into mission-critical failures.
Keep the Shield Strong
So why does your EMI gasket lose effectiveness over time? Compression set, galvanic corrosion, thermal stress, mismatched materials, and the slow drift of field conditions all conspire against it. Each mechanism leaves behind gaps and resistive layers that turn a once-tight shield into a porous boundary.
The solution isn’t just swapping in a new gasket when problems surface; it’s designing with longevity in mind, choosing the right materials, protecting against environmental stress, and planning for maintenance. That’s where companies like JEMIC step in: by matching gasket technology to the real conditions your equipment faces, you extend shielding life, maintain compliance, and prevent the slow creep of EMI back into your systems.