2006 Volume 55 Issue 10 Pages 531-535
This paper experimentally demonstrates that controlling AC distribution inside conductive material enables one to perform volumetric examination using electromagnetic phenomena. Several current distributions are superposed to locally realize AC distribution having a phase difference of 180 degrees between currents flowing near the surface and those deeply inside, and having non-exponential decay in depth direction. Experimental results clearly show that measuring the phase of magnetic field outside the material as a function of the ratio of the superposition provides information about the depth of defects quantitatively. In addition, this approach is applicable even though the depth of defects is much deeper than the standard depth of penetration; experimental results show clear differences between signals due to near-side notches 10, 12, 15, and 20 mm deep, when an exciting frequency of 100 kHz is adopted.
