Sensitivity images for multi-view ultrasonic array inspection

Abstract

The multi-view total focusing method (TFM) is an imaging technique for ultrasonic full matrix array data that typically exploits ray paths with zero, one or two internal reflections in the inspected object and for all combinations of longitudinal and transverse modes. The fusion of this vast quantity of views is expected to increase the reliability of ultrasonic inspection; however, it is not trivial to determine which views and which areas are the most suited for the detection of a given type and orientation of defect. This work introduces sensitivity images that give the expected response of a defect in any part of the inspected object and for any view. These images are based on a raybased analytical forward model. They can be used to determine which views and which areas lead to the highest probability of detection of the defect. They can also be used for quantitatively analyzing the effects of the parameters of the inspection (probe angle and position, for example) on the overall probability of detection. Finally, they can be used to rescale TFM images so that the different views have comparable amplitudes. This methodology is applied to experimental data and discussed.

Towards an Alternative to Time of Flight Diffraction Using Instantaneous Phase Coherence Imaging for Characterization of Crack-Like Defects

“…Each ray path can be composed of both the longitudinal (L) and transverse (T) wave modes, with or without reflection from the backwall. As the first and final legs of the ray path are in the wedge, which is only used for longitudinal wave propagation, they are omitted in the nomenclature [ 26 ]. For example, the TT-L path is made of a TT half-skip path (transmission) from the probe to the defect, and an L direct path (reception) from the defect to the probe.…”

A Model for Multiview Ultrasonic Array Inspection of Small Two-Dimensional Defects

“…In multi-view imaging, each full path is used to create a view. Because the FMC matrix is symmetrical due to the reciprocity of linear elastodynamics, algorithms based only on the times of flight, such as TFM, produce redundant views [17]. From these 6 paths, 21 views are unique out of a total of 36.…”

“…The back wall reflected for the path L-L was chosen because it provides a strong signal, clearly visible in all time traces. In a previous work [17], the front wall reflection was used instead; however, the back wall appears to be less sensitive to small probe misalignments and therefore provides a more robust estimation of the model scaling. A proper investigation would require a three-dimensional model to understand the effect of the out-of-plane misalignment in the front and back wall amplitudes.…”

Experimental Quantification of Noise in Linear Ultrasonic Imaging

“…The expected value h s is determined using the assumption that at any image point, the expected ACF of the measured speckle pattern is similar to the ACF of the imaging point spread function (PSF). With a forward model [32] based on the work of Schmerr [33], the PSF for each view can be precomputed for a given inspection setup. The model assumes a point scatterer and accounts for beam spread, directivity and transmission/reflection coefficients.…”