Planar Spiral Coil Design for a Pulsed Induction Metal Detector to Improve the Sensitivities

In a pulsed induction metal detector system, the sensitivity variation for detectable minimum metal target and the maximum detection distance are investigated as the winding geometry of the search coil is varied. A number of planar square spiral mono coils with various fill ratios and wire spacing-to-width ratios are comparatively analyzed based on a numerical simulation. Five representative coils are fabricated and applied to a pulsed induction metal detector system as a search coil. It is demonstrated that a search coil with a larger fill ratio has a high size sensitivity for a minimum metal target at close distances, which may be missed by coils with smaller fill ratios. A search coil with a smaller wire spacing-to-width ratio is shown to have a high depth sensitivity for maximum detection distances.