MFL PROBE WITH ASYMMETRIC CONFIGURATION OF GMR SENSOR-PERMANENT MAGNET DETECTING AND CHARACTERIZING THE ORIENTATION ANGLE OF SUPERFICIAL CRACKS IN STEEL STRUCTURES.

摘要

The probe presents an asymmetric configuration of GMR sensor-permanent magnet, as shown in figure 1. The direction of the magnetic field of the magnet is perpendicular the surface of the steel structure while the sensitivity axis of the GMR sensor is parallel the surface of the structure. When the probe is displaced over a surface with no cracks, the output voltage in the sensor is constant. On the other hand, when the probe is located over a crack, the value of the voltage of the sensor will vary with the width, depth and orientation of the crack. A GMR sensor is used as a sensitive element, thus the sensitivity in the probe will be independent from the displacement speed. The asymmetry of the GMR sensor-permanent magnet generates an operation point in the sensor and this is reflected in the base line of the output voltage profile of the GMR sensor. The probe may be used in restricted or difficult access places, where the electromagnets cannot be used. The main advantages of the prob e are the operations for estimating the angle of orientation of the crack without performing a complete mapping of the surface and the high sensitivity for characterizing cracks with widths lower than 1 mm.