Sensitivity of circular coils to conductivity changes: Analytical and numerical solutions

The method of contactless conductivity imaging is based on the magnetic-induction magnetic-measurement principle. In this study, the sensitivity of the circular coil used for measuring magnetic fields, to conductivity changes is investigated. To do so, the electrical circuit model of the receiver coil and that of the conductive object is developed. The conductive object is modelled as a thin disk (cylinder) coaxially placed inside the circular coil. Another cylindrical object is assumed to be coaxially placed within the conductive object. It is assumed that, the conductive object is placed within a time varying but spatially constant magnetic field. An analytic formulation is developed for the determination of the sensitivity of the circular coil to the variations of the radius and conductivity of the second object (inhomogeneity). The validity of the model is tested with numerical simulations employing the ANSYS magnetic simulation software. The nonlinearity error between the analytic and numerical solutions is calculated as 1.38% of the full scale for β=0.1, and 11.2% of the full scale for β=0.2.