Crack detection in steel using a GMR-based MFL probe with radial magnetization

This paper presents the development of a portable probe for detecting cracks in steel plates. The probe consists of a magnet and a giant magneto-resistance (GMR) sensor. The magnet provides a radial magnetization at the surface of the steel plate. The GMR sensor detects the tangential component of the magnetic flux leakage due to a crack in the steel plate. Two steel plates were inspected with six cracks of depths: 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm, and widths of 0.25 and 0.5 mm, respectively. The cracks were scanned with the GMR sensitivity axis at 90°, 80°, 70°, 60° and 50°. It is demonstrated that the output voltage of the GMR sensor is sensitive to the orientation of the crack.