Shielding effectiveness and the fourth purity decimal

The physics in one paragraph

Shielding effectiveness in a conductive mesh is the sum of three mechanisms: reflection at the mesh surface, absorption within the mesh volume, and multiple internal reflections. Each mechanism depends on the bulk conductivity of the material — which, in nickel, depends sharply on grain-boundary chemistry. Impurities at the grain boundary (particularly sulphur, oxygen and copper) scatter conduction electrons. At 99.8 % purity these impurities are a noticeable fraction of the grain-boundary mass; at 99.99 % they are not.

The frequency dependence

The improvement is not uniform across the spectrum. At low frequencies (below 1 GHz), reflection dominates and the improvement from NP1 is a modest 4–6 dB. At higher frequencies (5–16 GHz), absorption within the mesh volume dominates, and the improvement is 20–25 dB. Averaged across the ASTM D4935 sweep the number comes out around 18 dB^[1].

Fig. 1 — GTX NP1 mesh shielding effectiveness by frequency band. Source: Lectromec 2025.

Why it matters for 5G, defence and avionics

Wireless standards work on margins. A 5G base station targets 20 dB of isolation between adjacent channels; a defence avionics chassis targets 60 dB of external-emission suppression; a satellite payload targets 80 dB of board-to-board isolation at L-band. The 18 dB step from Class-1 to NP1 is the difference between "requires additional shielding layers" and "meets the requirement in a single mesh layer".

Operational consequences

• Mesh weight per shielded volume drops ~30 % at equivalent SE target.
• Thermal management improves because fewer conductive layers are stacked.
• Dielectric material budget increases, enabling more aggressive antenna geometries.