Effective cancellation of residual magnetic interference induced from a shielded environment for precision magnetic measurements

Using the method of inverse problem, we designed a cancellation coil that prevents a strong pulsed magnetic field inside a magnetically shielded room (MSR) from magnetizing and inducing large-scale eddy currents around the shielding materials. We implemented this coil with discrete current loops and evaluated it numerically and experimentally. Without the cancellation coil, the transient residual magnetic field in the middle of the MSR was greater than 0.1 mu T for 63.5 ms, while the cancellation coil reduced it to less than 0.1 mu T after 10.8 ms, shortening the decay time by 83.0%. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3643427]