Optimisation of ultrasonic array inspection of highly scattering materials

Optimization of ultrasonic array imaging performance for efficient defect detection in polycrystalline materials is an important practical problem that has gained significant attention. Although the primary physical factors affecting the propagation of ultrasonic waves in highly scattering materials are generally well understood, existing ultrasonic inspection optimisation approaches are mainly driven by empirical qualitative rules. The conventional quantitative measure for defect detectability is the signal-to-noise ratio (SNR), which is defined as the ratio of the maximum image amplitude of the defect to the root-mean-square amplitude of the grain scattering noise in the image. In this paper, a general model for the SNR is presented, incorporating both single- and multiple-scattering components, which is valid across all ultrasonic scattering regimes. This model is used to quantitatively analyse array imaging performance and provides the foundation for formulating quantitative guidelines that relate image SNR to array system parameters. The results are illustrated using both simulated and experimental data.