Attenuation (Shielding Effectiveness)

Attenuation is the reduction in the amplitude or power of a signal between two points. In the context of EMF shielding, it is often called shielding effectiveness (SE) and expresses how much of an incident electromagnetic wave is removed by a barrier. The standard unit is the decibel (dB).

The formula is SE(dB) = 10 · log₁₀(P_incident / P_transmitted), or equivalently 20 · log₁₀(E_incident / E_transmitted) for electric field strength. As a logarithmic unit, each 10 dB of attenuation represents a tenfold reduction in power: 10 dB cuts power to 10%, 20 dB to 1%, 30 dB to 0.1%, and so on.

For a conductive shield, attenuation arises from three mechanisms: reflection at the surface (driven by the impedance mismatch between air and the conductor), absorption within the conductor (the wave loses energy to induced currents), and multiple internal reflections. The total shielding effectiveness is the sum of these contributions in dB.

Real-world shielding effectiveness depends strongly on frequency, on the conductivity and thickness of the shield material, and — critically for meshes and fabrics — on aperture geometry. A shield that performs well at 2.4 GHz may perform much worse at 28 GHz millimeter-wave frequencies if the apertures are a meaningful fraction of the shorter wavelength.

Measurement is standardized in references such as IEEE Std 299 (for shielded enclosures) and ASTM D4935 (for planar materials). Quoted SE values for a fabric or material are only meaningful when paired with the frequency, the test method, and the geometry under which they were measured.

RADIHALT designs EMF protection blankets built around woven copper-nickel Faraday fabric. The terminology on this page — from Faraday-cage physics through attenuation figures and ICNIRP exposure limits — is what underpins the engineering and the claims we publish about our products.

We try to keep our marketing language tied to the same vocabulary regulators and physicists use. If a definition on this page conflicts with anything on a RADIHALT product page, the glossary entry is the source we hold ourselves to.