Estimation of Mutual Induction Eddy Current Testing Method Using Horizontal Exciting Coil and Spiral Search Coil

The mutual induction type eddy current testing using a spiral type search coil is one of the eddy current testing (ECT). In this type ECT probe, since the thickness of a spiral search coil is very thin, the distance (lift-off: L o) between the ECT probe and the specimen is able to set small. Therefore, the high detection sensitivity is obtained. However, since the wire is coiled in the shape of spiral, the evaluation of the flux density inside the spiral search coil is made difficult by experiment. Moreover, the phenomenon elucidation of inspection using this ECT probe is not carried out. In this paper, the inspection characteristic of a surface defect on an aluminum plate using this probe was investigated by 3-D alternating electromagnetic finite element method (FEM). Moreover, the evaluation in consideration of the characteristic of the spiral search coil in this ECT probe is also investigated by (1 + 1) evolution strategy. It is shown that high detection sensitivity is obtained using the spiral search coil.