How to Calculate Shielding Effectiveness: Absorption (A), Reflection (R) & Multiple Reflection (B)

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For a continuous sheet of conductive material, the shielding effectiveness can be estimated by the three terms formula. It includes the two principal mechanisms that reduce the field intensity : 1) absorption (A), 2) Reflection (R) and 3) Multiple Reflection (B).

The absorption loss, A expresses the energy dissipation that occurs when a field propagates through a conductor.
As the field propagates through the shield of thickness t (cm), it is attenuated exponentially.

A shield also impedes an electromagnetic wave by reflection loss

When the absorption losses are small, the energy reflected back into the shield at the second boundary cannot be ignored. This is true in the case of thin shield. As a result, we need to consider the effect of multiple reflection for magnetic field shielding effectiveness.

The term B in the shielding effectiveness equation accounts for the re-reflection. B is always negative