Mitigation of background field effects on coils characterization from magnetic measurements

In magnetic systems where small discrepancies of field map from the design value may strongly impact on the device performance, quality insurance procedures are foreseen to verify how each single coil meets the design criteria. External magnetic measurements can be used to estimate the possible deformations of conductors inside the magnet, but this implies inverse problem approaches. The measurement accuracy and the background field rejection are therefore critical; as a consequence, the measurement system must be carefully designed, taking into account several elements, including the probes characteristics, the characteristics of the windings and of the surrounding environment. In this paper, a possible numerical pre-processing of measured data to reduce the impact of background field is proposed. The method is based on a spectral decomposition of the gain matrix, and a filtering based on the projection of measurements on the matrix eigenvector basis.