Perhaps a physicist or radio engineer can spot an error in here:
The radio skin depth formula can be simplified to:
where p is the resistivity measured in Ωm and μ is the relative magnetic permeability of the medium. Mild steel can have a μ of around 300 (although I’ve seen some references to as high as 2000) at f=10kHz with p=0.00000015 Ωm. (My regrets, but it’s taking far too much work to write 1.5 x 10 ^-7 in scientific notation on WordPress).
Substituting for the lower magnetic permeability I get a 10kHz radio skin depth of mild steel to be about 0.1 mm. Substituting the higher permeability I get a radio skin depth of about 0.05 mm.
Thickness δ attenuates to about 38.78% of the surface strength. What, then, counts as “complete shielding”? Using the more conservative value, a 1.2 mm thickness of mild steel provides 12 skin depths and excellent shielding,