A reduction in magnitude of electromagnetic field strength is commonly referred to as Magnetic Field Attenuation. This reduction can be measured and expressed by decibels (db). When shielding materials are introduced they provide this magnetic field attenuation by absorption, reflection, scattering and dispersion.
Calculated magnetic field attenuation can be represented as:
Attenuation (dB) = 20 Log E1/E2
E1 = Field intensity generated on one side of the shield.
E2 = Field intensity received on the other side of the shield.