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Previously we have succeeded in exploiting a new high sensibility eddy current testing (ECT) sensor called the infinite (∞) coil. Operating principle of this ∞ coil is that two adjacent coils constructing the north and south poles alternatively set a zero magnetic potential region and keep the same situation when eddy currents are flowing along the paths in parallel to the exciting coils. If the eddy currents could not flow the paths in parallel to the exciting coil on the test specimen, then a zero magnetic potential region between the two exciting coil moves toward the other position. This means that a sensing coil located at a mid position of two exciting coil is possible to detect the disturbed magnetic fields, i.e., the defect in the test specimen could be detected from the sensing coil signal. In the present paper, consideration of the practical flat/film ∞ coil design leads to an employment of the two rectangular shape exciting coils. Practical experiments and 3D FEM simulations verify the validity of our practical design policy of the flat/film∞ coil. [ABSTRACT FROM AUTHOR]

Previously, we have proposed an infinity coil as a high sensibility ECT sensor. This paper has evaluated a possibility of the backside defect searching by the low frequency excitation of a modified infinity coil whose exciting coils are the flat/film shape to fit to the curverved test targets. In the present paper, we have elucidated the lift-off characteristics of the backside defect searching when employing the low frequency excitation to our flat/film shape infinity coil. [ABSTRACT FROM AUTHOR]