Investigation into the use of inductive coil arrays for metal identification

The work presented in this paper investigates through finite element simulation and experimental data the physical implications of designing coil arrays for identifying metal objects. There has been a substantial amount of research into using printed circuit coil systems for this application but the investigations have been confined to the physical construction of the coils, design circuitry and interpretation of the resulting signals. This work shows that the excitation coil geometry can be optimized to improve the homogeneity of the magnetic field in the sensing region, and that the ratio of diameters of the sensing coil to the object determine both the resolution and uniqueness of the mutual impedance. Finally, finite element simulations have been used to explain the reduction in mutual coupling of aluminum samples when compared to an identical steel one at 15 kHz.