Frequency dependence of shielding effectiveness of multilayered magnetic shields

An analysis of magnetic shielding effectiveness of multilayered structures versus frequency is presented. It is shown that the quasistatic field approximation is accurate until several MHz depending on the source-to-observation-point distance, characteristic dimensions of the source, and physical and geometrical properties of layers. The accuracy is assessed by means of comparisons with the solution of the wave equation in a wide frequency reange. This study can be useful for the shield design and also for predicting the shielding effectiveness of multilayered magnetic shields in a source of non sinusoidal periodic magnetic fields.