Optimal Extraction of Ultrasonic Scattering Features in Coarse Grained Materials

Abstract

Ultrasonic array imaging is used in non-destructive testing for detection and characterisation of defects. The scattering behaviour of any feature can be described by a matrix of scattering coefficients, called the scattering matrix. This information is used for characterisation, and contrary to imagebased analysis, the scattering matrix allows characterisation of defects at the subwavelength scale. However, the defect scattering coefficients are in practice contaminated by other nearby scatterers or significant structural noise. In this context, an optimal procedure to extract scattering features from a selected region of interest in a beamformed image is here investigated. This work proposes two main strategies to isolate a target scatterer in order to recover exclusively the time responses of the desired scatterer.In this paper such strategies are implemented in delay-and-sum and frequency-wavenumber forms, and optimised to maximise the extraction rate. An experimental case in a polycrystalline material shows that the suggested procedures provide a rich frequency spectrum of the scattering matrix and are readily suited to minimise the effects of surrounding scattering noise. In doing so, the ability to deploy imaging methods that rely on the scattering matrix is enabled.

Exploring 3D elastic-wave scattering at interfaces using high-resolution phased-array system

“…On the other hand, the 3D scattering intensities were examined only for the oblique incidence of the transverse wave. As reported in past studies of 2D scatterings 18 , 20 – 22 , 50 , ultrasonic scatterings at cracks can involve mode conversion, such as from transverse waves to longitudinal waves. We can investigate mode-converted scattered waves at cracks in the same manner simply by selecting V L instead of V T as V j in Eqs.…”

“…S4 (Supplementary material), the perfect avoidance would be impossible. To suppress this problem, the utilization of focusing would be useful, as demonstrated for 2D scattering analysis 18 . For instance, the use of a point-focusing incidence instead of the plane-wave incidence would be effective since observable scatterers can be limited in the vicinity of the transmission focal point.…”

“…Given that ultrasonic crack inspections utilize the scattering phenomena at cracks, understanding the elastic-wave scattering at cracks is indispensable. Thus far, most studies on ultrasonic scattering at cracks have been limited to two dimensions 18 , 20 – 23 . On the other hand, an actual crack is composed of multiple scattering sources since crack faces have microscopic asperities 24 and parts of the faces are sometimes in contact 25 .…”