Display Defects In The Metal Plate Under The Sensor Disturbance Magnetic Field Distribution

The Alternating Current Field Measurement (AMFM) technique is a new electromagnetic non-destructive testing (NDT) technique able to quantitatively measure the dimensions of surface cracks of metallic components. First, the state-of-the-arts of AMFM was introduced in this paper. And then the finite element method (FEM) of a 3D whirlpool field was described in detail, based on analysis of its characteristics and basic principles. The possibility of increasing the amplitude of the signal by adding a magnetic core and that of improving the pick-up signal by adding a magnetic field sensor were researched with single rectangle exciting coil, based on the point-by-point simulation. Three kind of array sensors: the array sensors of exciting coil , the array sensors of check-up coil and the array sensors of exciting coil and check-up coil, were simulated. The characteristics of the distribution of the perturbed magnetic-field and the measurement path were researched and the quantitative relation between the magnetic-field and the parameters of the cracks was confirmed. And further, the quantitative relation in the first and third instances mentioned above was analyzed. The validation of the simulating results and the practicability of the array sensors were confirmed by practical experiments. Finally, some conclusions of the paper and suggestions about the further study were provided by the author.