Theoretical and experimental verification of the properties of superconductor surface imaging

Electric currents in the vicinity of a superconductor induce surface currents which contribute to the complete expression for the magnetic field. The solution can be written in terms of a magnetic scalar potential that satisfies the Neumann condition at the superconducting boundary. A sensing coil whose axis is normal to the surface detects a field component which is the sum of these direct and induced current contributions. As a result of this imaging effect, a single coil acts like a first order gradiometer. Furthermore, it can be shown that the surface deflects noise from distant sources. An experimental verification of the properties of the superconductor surface imaging discussed here is presented. The primary application of the principles considered here will be the sensing of extremely weak magnetic fields, such as those encountered in magnetoencephalography, nondestructive evaluation, and corrosion analysis.<>