Performance of circular and square coils in electromagnetic–thermal non-destructive inspection

The performance of circular and square coils in electromagnetic–thermal non-destructive inspection of conductive plates is investigated numerically for various configurations. A coil is most effective when placed at an optimum distance from the plate, equal to 1/4 of the diameter for a circular coil or 1/4 of the side for a square coil. At this distance, the coils considered are equally efficient in detection of cracks. Substantial differences exist only when the coils are placed very close to the plate but then become less effective. For that case, the planar coils give better results. A coil with a section comparable in area with the inspected surface cannot inspect the whole surface effectively in a single inspection. The support of a smaller section coil is necessary in order to clarify the shape of the cracks that are not clear.