Magnetism-current inverse in high-temperature superconducting quantum interference device magnetic field measurement

Based on the Biot-Savart law, spatial filtering technology and two-dimensional Fourier transform, the inverse problem of magnetic field to current distribution was researched. The inverse method was applied to the real magnetic field data measured by a high-temperature superconducting quantum interference device (SQUID), and the magnetic field was produced by a lead with current and vortex around a columniform crack. The inverse results, especially how to select the filtering frequency in a Fourier space, were discussed. The results show that a larger cutoff frequency can improve the spatial resolution of the current image, but increase the noise signal. If a smaller cutoff frequency is selected, much of the noise can be eliminated, but the resulted inverse signal will be anamorphic, and the spatial resolution is decreased. Using the magnetic field data excited by vortex around a column form defect, the inversed current result can give the information about the location and the form of the defect exactly.