Developments of flat ∞ coil for defect searching in the curved surfaces

Previously we have succeeded in developing a new ECT sensor called ∞ coil. This new ECT sensor is a relatively high sensibility and has the high liftoff characteristics compared with that of conventional ECT sensor. However, the ∞ coil confronts to a serious difficulty to apply the curved surface specimens. To overcome this difficulty, this paper has worked out a flat ∞ coil. This flat ∞ coil exhibits a high sensitivity not only to the curved surface but also to the flat surface specimens because of its highly shape flexibility to fit the curved target surface and widely spreader-able exciting coils. Intensive numerical simulations employing 3D FEM have been carried to show the usefulness of the flat ∞ coil. The experimented results have verified the validity of the numerical simulations. Thus, we have confirmed the versatile capabilities of the flat ∞ coil. (author)