Magnetic shield enclosure door penetrations

Magnetic shield  enclosure door penetrations in a six-sided magnetic shield compromises the effectiveness of the shielding to some degree. For a highly conductive lossy magnetic shield, holes in the shield creates not only voids without shielding, but also reduce the conductivity of the shield both locally and globally. Less conductivity reduces the eddy currents and back EMF generated.  The door penetration is usually the largest and most difficult penetration into a shielded room. Vitatech used a ten-foot square ¼” thick seam welded 1100 aluminum enclosure set up for testing and calibration. Three configurations of a 7 foot by 4 foot door and one configuration without a door were tested. The table #1 below shows the results.  It is clear from these tests that, in any critical EMI environment, the magnetic shield enclosure door penetrations should be kept to a minimum. Removable panels with overlapping aluminum are far more effective than a electrically isolated ¼” door shield.