Abstract
This paper describes a new non-destructive testing instrument that searches for defects on the steel surface opposite that into which H-coil and the exciting coil are built Defects can be found with the H-coil by measuring changes in the eddy current. In this case, defects on the surface of the steel can be found according to the skin depth of the eddy current. Therefore, a moving magnetic field is effective for defects on the opposite surface of the steel, because much information is derived from the moving magnetic field in comparison with an alternative magnetic field. The shape and structure are also important to improve the sensibility of the testing instrument. In this paper, we present some results obtained with our new non-destructive testing instrument, and discuss the possibility of detecting defects in the opposite surface and subsurface region of the steel.
