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Magnetic Shielding Material
Mu metal
Home / Mu metal / Calculation of Shielding
Calculation of Shielding October 18,2017.
Much about Mu Metal magnetic shielding was discussed previously, then what is field attenuation? It’s also called shielding factor (S), which is a ratio between the magnetic field strength outside of the magnetic shield (Ha) and the resultant field on the inside of the shield i.e. Ha/Hi (no units) or S = 20 × log(Ha/Hi) (Db).

There are many different calculation formulae according to the permeability of the materials, the material thicknesses, and the shape & size of the shields:

For a cubic shielding box:
S = 4/5 × (μ× d/a)

For a closed shielding can:
S = 4/3 × (μ × d/D)

For a long hollow shielding cylinder in a magnetic transverse field:
S = μ × d/D

In the case of multiple layer shields with air gaps provided by insulating spacers, the shielding factors of the individual shields are multiplied together resulting in excellent shielding factors.

For a double layer shield:
S= S1 × ((S2 × (2 × change in diameter /diameter))
Anyway, in most cases these formulae are approximate only.
Remarks:
μ: relative permeability
a: box side length
d: material thickness
D: shielding diameter

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