An Efficient Method for Output Prediction of an Array Waveguide Probe When Scanning a Surface-Breaking Crack in a Metal

The use of array probes in non-destructive inspection of materials and components offers several advantages over conventional single-element probe testing method, including faster inspection time, larger coverage area in one pass, and more efficient probe lift-off noise suppression. The paper proposes an efficient modeling technique to predict the output signals of an array of open-ended rectangular waveguide probe when interrogating a surface-breaking crack in a metal. The proposed technique involves two stages. First, a method-of-moments formulation is adopted to characterize the array probe by evaluating its S-parameters in free space. This stage provides a flexible framework that enables one to determine the incident field for a desired probe excitation mode. The incident field in each excitation mode can then be used to analyze the probe-crack interaction from which the orientation, location and dimensions of a crack can be inferred. The validity and computation efficiency of the proposed modeling technique is demonstrated by comparing the simulation results of a prototype 2 × 2 cell X-band array probe with the experimental data and those obtained using a commercial finite integration technique code. It has also been shown that appropriate inversion curves could be obtained to determine the unknown quantities of a crack (depth, length, width, location and orientation) without resorting to a mechanical scanning of the workpiece.