Efficient model of wave scattering from large defects in ultrasonic array inspections

The Full Matrix Capture (FMC) technique and its related post-processing algorithms can provide improved array image quality and accurate defect characterisation. Therefore, there is an increasing demand for efficient simulation tools to generate FMC array data sets to optimise array configurations for defect's detection and characterisation. A hybrid ray-tracing technique combined with the far-field scattering response of the defect (defect's far-field scattering matrix) represents a fast and efficient modelling tool, but relies on the far-field assumption. When the scatterer is large, or located close to the array, the far-field assumption becomes inaccurate, and the model breaks down. In this paper the near-field model of ultrasonic array data for immersion and direct contact measurement configurations is developed. It is shown that the near-field scattering behaviour can be extracted from the far-field scattering matrix. The model is validated using experimental measurements and its performance is illustrated on modelling and experimental examples.