Scan Type Magnetic Camera Images with a High Spatial Resolution for NDT Obtained By Using a Linearly Integrated Hall Sensors Array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on the magnetized specimen by using a magnetic sensor such as the Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface crack on magnetized ferromagnetic materials. A scan type magnetic camera, based on the principle of MFLT, uses inclined Hall sensors array on the printed circuit board (PCB) to detect small cracks in high speed. However, the waveforms appear in the direction perpendicular to the scan, because the sensors are bonded at different gradients and heights on a PCB in spite of careful soldering. In this paper, the linearly integrated Hall sensors (LIHS) on a wafer are proposed to minimize these waves and to improve the probability of crack detection. The specimen took from a billet is used to determine the effectiveness of the LIHS in the multiple cracks detection.