Enhance the sensibility of the film infinite eddy current sensors

Previously, we have succeeded in exploiting a new high sensibility eddy current testing 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. This paper proposes one of the enhancing methodologies of the infinite coil sensibility. Key idea is that the zero magnetic potential region between the north and south exciting poles of the infinite coil is increased by changing the circular to the semicircular shape of the exciting coils. Numerical as well as experimental results verify the validity of this idea