Abstract Previously we have succeeded in developing a new ECT sensor called ∞ coil. This new ECT sensor is higher sensibility than those of the conventional ones. 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 higher sensibility compared with those of the first ∞ coil because of a realization of operating principle. Further, this flat ∞ has a versatile abilities to the target specimens having any geometrical shape. Intensive numerical simulations employing 3D FEM have been carried to show the usefulness of the flat ∞ coil. Also, the experimented results have verified the validity of the numerical simulations. Thus, we have confirmed the distinguished capability of the flat ∞ coil.