Magnetic sheet-backed search coil for pulsed-induction metal detector system

Magnetic sheet backing of the search coil is proposed to improve the detection range of a pulsed-induction (PI) metal detector (MD) system. A planar square spiral mono coil is printed on an FR-4 substrate, and layers of magnetic sheets are attached to the substrate. The coil geometry is modelled using the finite-element method, and the static magnetic field distributions are compared. With the magnetic sheet backing, the magnetic field is shown to increase in the target direction and to decrease in the opposite direction. The coils are fabricated and applied to a PI MD system. It is demonstrated that the proposed magnetic sheet-backed search coils have longer detection ranges than the coil without magnetic sheet backing.