An improved sensor for the magnetic susceptibility imaging technique for detecting impurities in non-ferromagnetic materials
Résumé
A cantilever-based sensor of magnetic force is a potential tool for magnetic susceptibility imaging in bulky materials. To solve the limitations of the previously reported sensors, in this study, a Hall device is employed to measure the magnetic field variation caused by the displacement of sensing magnet attached to the free end of the cantilever. The improved sensor has the smaller size and the higher lateral resolution and the adopted permanent magnet can be attached onto the cantilever’s free end to improve its sensitivity to the magnetic susceptibility. Based on the improved sensor configuration, two types of sensors are presented and their performances are experimentally investigated. Type-1 sensor with the cylindrical sensing magnet with a diameter of 5 mm is capable of detecting a cubic impurity (with a side length of 1 mm) of 304 stainless steel or aluminum with a depth of 1 mm in a photosensitive resin block. Type-2 sensor employs a sensing magnet with a diameter of 1.2 mm and possesses higher lateral resolution than Type-1 sensor. The estimated sensitivity of Type-2 sensor is about one third of that of Type-1 sensor. Although the impurity of aluminum and even resin cannot be distinguished from the air background in the magnetic susceptibility imaging results obtained by Type-2 sensor, the cubic impurity of 304 stainless steel can be successfully detected by Type-2 sensor.