EFFECT OF AC MAGNETIZATION ON SHIELDING IN SLOWLY VARYING MAGNETIC FIELDS.

The effect of ac magnetization on shielding against an external magnetic field varying over a range of plus or minus 3 Oe in single, double, and triple shields is investigated experimentally. The ac magnetization is realized by passing 50-Hz line current directly through the ferromagnetic walls of the shield. The shielding factor is increased, the hysteresis is reduced, and the dependence of the shielding factor on external field is eliminated. The magnetization is more effective with multiple shields. The improvement in the shielding depends significantly on how the wall joint is oriented relative to the external magnetic field.