When you build a loop antenna, it's common to wrap it in, e.g., aluminum
foil that's grounded so as to prevent electric field pick-up (I'm thinking
of HF loops here, 30MHz). A slit is made in the wrapping so that a shorted
turn isn't created, thereby nulling out the magnetic field that the loop is
trying to detect in the first place.

Something I don't understand, though... normally, if you were thinking of
using aluminum for EMI shielding purposes, the skin depth of aluminum at
10MHz is all of ~1mil. Hence, a regular sheet of aluminum foil would
significantly attenuate both the magnetic and electric fields on its 'far'
side. Why doesn't this apply in the case of a shielded loop antenna? It
seems to me that the ~95+% 'coverage' of the shield (everything minus the
slit to prevent the shorted turn) would be what dictates the overall
shielding effectiveness, not the presence of the slit itself.

Looking for insight,
---Joel Kolstad