Defect detection in embedded reinforcing bars and cables using a multi-coil magnetic field sensor

A nondestructive testing system which detects surface defects in steel bars or cables embedded within reinforced or pre-stressed concrete is described . The component under test is energized by an alternating current of suffic ient frequency to ensure that current flows takes place on the surface of t he steel. Detection coils, in conjunction with a suitable amplification sys tem, are positioned at various alignments with respect to the steel bar or cable, and thereby detect, through mutual induction, both the dominant Row path and the deviated current Row in the vicinity of a defect. The output s ignals from the multi-coil array are converted and fed to a computer for st orage and processing. This system has clear relevance to the civil engineer ing nondestructive testing industry.