Abstract: To meet the demand for defect visualization in alternating current field measurement (ACFM) technique, a double U-shape orthogonal inducer array is introduced. This excitation method induces a rotational electromagnetic field, which effectively avoids the influence of defect orientation on detection and provides sufficient signal data for defect visualization. The inversion methods of surface shape and cross section shape of defect are proposed on the basis of the rotational electromagnetic field. The results of FEM simulation analysis show that the average relative errors of these inversion methods are less than 10%. Verification tests are carried out for these inversion methods by using the ACFM testing system built in the laboratory, and the results prove that these methods are simple and feasible, and can effectively realize real-time defect visualization for ACFM.

Key words: Alternating current field measurement, Inducer array, Nondestructive testing, Simulation analysis, Visualization