Basic principles of electromagnetic shielding
The effectiveness of a shield is not solely determined by its structure. To achieve proper electromagnetic shielding, the design must follow fundamental principles. There are two core principles that govern effective electromagnetic shielding:
In general, most metal materials can provide more than 100dB of shielding effectiveness, especially against high-frequency fields. However, in real-world applications, achieving over 80dB is quite challenging. This is due to several factors that compromise the integrity of the shield.
First, **electrical continuity** is essential for a shield to function properly. The shield must be a continuous and complete conductor. In practice, this is difficult to achieve because a fully enclosed shield is not practical. Most enclosures have openings—such as vents, display ports, mounting holes, or gaps between panels—that break the conductive path. If these discontinuities are not addressed during the design phase, the shielding performance can drop significantly, sometimes even rendering it ineffective.
Second, **no direct conductors should pass through the shield**. Even a single wire passing through the shielded enclosure can reduce the shielding effectiveness by up to 99.9% (or 60dB). In reality, cables are always present—power lines, signal cables, etc.—and if they are not properly shielded or filtered, they can severely degrade the overall shielding performance. Proper cable management and filtering are critical components of an effective shielding strategy.
*(Sometimes, the presence of a single conductor piercing the shield can be more detrimental than seams or gaps.)*
Lastly, **the shield does not need to be grounded for electromagnetic shielding**. While grounding is necessary for electrostatic shielding, it is not required for electromagnetic shielding. The effectiveness of the shield is independent of whether it is grounded or not. Although grounding may influence the electromagnetic environment in some cases, it doesn't directly affect the shielding performance. Therefore, designers should not assume that grounding improves shielding—it's more about how other factors are managed.
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