Two Dimensional Inversion of Crack Signal in Surface Electromagnetic Field Measurement Technique

Abstract

Surface electromagnetic field induced in metals have been successfully exploited for detecting and sizing surface cracks. In the two methods of the surface magnetic field measurement (SMFM) and the induction ac potential-drop (IACPD) reported in [1,2], the surface field is produced by U-shaped wires or rectangular coils carrying high frequency currents. In the SMFM technique, the surface magnetic field is interrogated by a non-contacting magnetic field sensor located in the vicinity of the metal surface whereas in the IACPD technique, a contacting two-legged electric field sensor is used for sampling electric potentials at the metal surface, Figure 1. In both techniques, the surface field is discontinuous at the crack lips. The inducer and the sensors, which can be attached together as part of one probe, as well as other components required for signal detection are shown in Figure 1 [3].