![]() Demagnetization requires a negligible environmental field. A low magnetic field and low field gradients inside the shield can be obtained by demagnetization (degaussing) with a decreasing alternating current through demagnetization coils. Because of the finite remanence of the permalloy the shield has to be degaussed to eliminate inevitable magnetization. Afach et al., “ Revised experimental upper limit on the electric dipole moment of the neutron,” Physical Review D 92, 092003 (2015). Beside a high shielding factor for AC magnetic signals, also a low residual field and residual field gradients become limiting for the basic physics experiments. Bales et al., “ A large-scale magnetic shield with 10 6 damping at millihertz frequencies,” Journal of Applied Physics 117, 183903 (2015). ![]() Babcock et al., “ A magnetically shielded room with ultra low residual field and gradient,” Review of Scientific Instruments 85, 075106 (2014). At present, the highest requirements for large scale magnetic shields are from fundamental physics experiments. Their size varies from a few cm 3 for speedometers in cars to magnetically shielded rooms (MSRs) to measure e.g. Magnetic shields made from permalloy are commonly used to protect measuring equipment and experiments against environmental magnetic field changes.
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