Mu-metal is an alloy of primarily nickel and iron, with high magnetic permeability 1. It provides a low resistance pathway for external magnetic fields to flow, thereby 'shielding' the area housed within 1. It is therefore a useful component of the housing for medical imaging devices which require shielding from external magnetic fields 2.
The effectiveness of the metal to shield from magnetic fields is defined by the shielding factor 'S' where S is calculated as the ratio of the magnetic field at a point in the absence of shielding (Ha) to the magnetic field inside the shielding (Hi) 1:
S = Ha/Hi
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