The generic shielding effectiveness requirement is 40 dB for
magnetic field, electric field, and plane waves. Depending on the application
the frequency range can start from 10 Hz going up to GHz.
To predict shielding effectiveness (SE) of a metal sheet the
following factors are summed: Absorption
Loss (A), Reflection Loss (R), re-Reflection Correction Factor (C). SE = A
+ R – C (see MIL-HDBK-419A).
Absorption loss depends on material thickness, permeability,
electrical conductivity, and the frequency of the incident wave. It is the same for all electromagnetic waves.
Reflection loss depends on the distance of the
EMI source to the material (different for electric, magnetic, and plane waves),
material electrical conductivity, and the frequency of the incident wave.