Abstract
The authors propose a surface eddy current probe for flaw depth evaluation with minimal lift-off noise. The probe consists of a tangential exciting coil and two tangential detecting coils arranged on either side of the exciting coil. These detecting coils do not pick up eddy current induced in flawless material but do pick up the current induced in flawed material. Thus the new probe can detect surface flaws without lift-off noise in principle.
Experimental results with the new probe have indicated that it generates only minimal lift-off noise compared to the conventional surface probe. The phase of flaw signal changes according to the depth of slit flaws but is changed little by the length, width, or direction. Thus the new probe makes it possible to evaluate the flaw depth based on the phase of flaw signal. The probe can also eliminate the cumbersome bridge balance procedure that is a necessary for conventional eddy current testing.
