[RFEngineer]

From Wikipedia:

"Mu-metal is a nickel-iron alloy (77% nickel, 15% iron, plus copper and molybdenum) that is very efficient for screening magnetic fields."

a simple faraday cage, or screen will still be penetrable by the magnetic portion of an EMP. Mu-metal directs the magnetic portion around an enclosure.

[investigateworld]

I know where there's a bunch of abandoned mines going mines into the earth. Would the contents therein be EMP proof without additional shielding?