Contents I. Introduction
Eddy-Current inspection has proved to be a fast and effective nondestructive technique to detect and size flaws that occur in metallic tubes, such as steam generator tubes. Conventionally, eddy-current probes such as bobbin coil probes cannot detect circumferentially oriented defects; rotating coil probes can obtain an eddy-current C-Scan of tube so that the circumferential defects are detected but the inspection using rotating probe coils scanning along a helical path takes too much time. Also, the complex mechanical rotation affects the data quality and reliability of the probe [1]. Array probes are capable of determining circumferential location of defects on the tube and have high inspection speed, but need complicated excitation and data analysis system [2]. Rotating magnetic field probe, generating rotating field electronically without mechanical movement, can combine the merits of previous three types of probes and avoid their disadvantages. M. Enokizono presented a rotational magnetic flux sensor, which is consisting of two pairs of exciting coils perpendicular to each other and one three-axis search coil centered between exciting coils [3]. However, the probe is designed for planar test samples and also just sensitive to backside cracks of ferromagnetic plate. T.E. Capobianco proposed a probe composed of orthogonal excitation coils to generate rotating magnetic field (RMF) and pancake pickup coil [4]. R. Grimberg developed many kinds of RMF probes for different applications involving steel wire and ferromagnetic tube test samples [5], [6].
