Optimization of element length for imaging small volumetric reflectors with linear ultrasonic arrays

Abstract

Abstract. A 3D ultrasonic simulation study is presented, aimed at understanding the effect of element length for imaging small volumetric flaws with linear arrays in ultrasonically noisy materials. The geometry of a linear array can be described by the width, pitch and total number of the elements along with the length perpendicular to imaging plane. This paper is concerned with the latter parameter, which tends to be ignored in array optimization studies and is often chosen arbitrarily for industrial array inspections. A 3D analytical model based on imaging a point target is described, validated and used to make calculations of relative Signal-to-Noise Ratio (SNR) as a function of element length. SNR is found to be highly sensitive to element length with a 12dB variation observed over the length range investigated. It is then demonstrated that the optimal length can be predicted directly from the Point Spread Function (PSF) of the imaging system as well as the natural focal point of the array element from 2D beam profiles perpendicular to the imaging plane. This result suggests that the optimal length for any imaging position can be predicted without the need for a full 3D model and is independent of element pitch and the number of elements. Array element design guidelines are then described with respect to wavelength and extensions of these results are discussed for application to realistically-sized defects and coarse-grained materials.

Pit to crack transition and corrosion fatigue lifetime reduction estimations by means of a short crack microstructural model

“…Recent NDE developments show promising opportunities for characterising defect acuity/shape. For instance, the concept of Full Matrix Capture (FMC) for ultrasonic applications [21], the application of data-fusion through modern ultrasonic array imaging techniques [22,23] and parametric-manifold mapping [24], among others. In any case, the detection of the earliest stages of pitting and cracking will remain challenging for state-of-the art NDE techniques applied, where a tradeoff between the ease of implementation and resolution is typically observed [25].…”