Shielding Effectiveness

SE = 20 × log₁₀(E_inc / E_trans)

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Result
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Formula

SE = 20 × log₁₀(E_incident / E_transmitted)

Description

Shielding effectiveness quantifies how well an enclosure or barrier attenuates electromagnetic fields, expressed in decibels. It is the ratio of the incident field strength to the field that passes through the shield. Higher SE values indicate better shielding. SE consists of three components: reflection loss (impedance mismatch at the shield surface), absorption loss (energy converted to heat as the wave passes through the material), and multiple reflection correction (significant only for thin shields at low frequencies).

Variables

  • SE — Shielding effectiveness (dB)
  • E_inc — Incident electric field strength (V/m or arbitrary units)
  • E_trans — Transmitted electric field strength after shielding (same units)

Practical Notes

Typical SE requirements: consumer electronics 20-30 dB, industrial equipment 30-60 dB, military/medical 60-100 dB. In practice, SE is limited by apertures (ventilation holes, seams, cable penetrations) rather than the shield material itself. A 1 mm gap in an enclosure can reduce SE by 20-40 dB at GHz frequencies.

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