Shielding Effectiveness Calculation Reference Tables (Copper/Aluminum/Steel)

Shielding effectiveness quantifies the reduction in field strength (electric, magnetic, or electromagnetic) achieved by an intervening conductive barrier, expressed logarithmically in decibels (dB). For lightning and surge protection engineering, SE is critical because fast-rising transients (e.g., 1–100 MHz components of lightning-induced currents) can couple into sensitive electronics via radiated or conducted paths; effective shielding mitigates this coupling. Copper and aluminum—non-magnetic, highly conductive materials—provide strong reflection-dominated shielding at high frequencies (>1 MHz), while steel (ferromagnetic, lower conductivity but higher relative permeability μᵣ ≈ 100–1000) excels at low-frequency magnetic field attenuation (<100 kHz), making it preferred for shielding against lightning’s quasi-static H-field component. Reference tables typically tabulate SE as a function of frequency (e.g., 10 kHz–1 GHz), material type, thickness (e.g., 0.5 mm–3 mm), and field source geometry (near-field vs. far-field), often derived from the classical three-term SE model: SE = R + A + B, where R is reflection loss, A is absorption loss, and B is correction term for multiple reflections (often negligible for t > δ). These tables are embedded in standards-based design workflows (e.g., IEC 62305-2, IEEE Std 1100) and used alongside empirical corrections for seams, apertures, and grounding continuity—factors not captured in idealized tabular data but essential for real-world implementation.