Volumetric imaging through a doubly-curved surface using a 2D phased array

Abstract

Ultrasonic phased arrays have become widely used in recent years in non-destructive testing (NDT). However, most NDT arrays are 1-dimensional (1D), which generate 2dimensional (2D) images from a single position and lack the ability to focus accurately through surfaces that are curved in multiple directions. In this paper, a 2D phased array is used to experimentally image artificial defects (represented by bottom-drilled holes and electrical discharge machined notches) within a test specimen with a doubly-curved surface profile in an immersion configuration. The array is mechanically scanned above the entire surface of the specimen and the 3-dimensional (3D), or volumetric, images generated at each position are combined to produce a single image of the specimen's entire surface. The surface profile is then extracted and discretised for interior volumetric imaging. The results show that the root mean square (RMS) error between the ultrasonically extracted surface and the true surface is 0.04 mm and 95% of absolute errors are less than 0.07 mm. Finally, the positions of visible defects are measured, using (i) the depth above the back wall and (ii) the lateral distance from a notch on the specimen's surface, and compared to their true values. The study shows that the standard deviation of depth and lateral position measurements is 0.68 mm and 0.89 mm respectively. Defects that are located beneath regions of sufficiently steep surface curvature were unable to be imaged.

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

“…Here, we selected two scanning conditions to examine the importance of utilizing ultra-multiple elements for the high-resolution 3D imaging of fatigue cracks. One condition employed 256 receiving points (i.e., 16 × 16) to simulate the maximum number of elements for a piezoelectric 2D matrix array 28 – 31 . The other condition employed 4047 receiving points (i.e., 71 × 57) to demonstrate the high-resolution 3D imaging capability of PLUS.…”

“…However, such PA systems have prohibitive costs and technical difficulties. Hence, the number of piezoelectric 2D array transducers is typically less than 256 for nondestructive testing (NDT) applications 28 – 31 , although state-of-the-art medical ultrasonic imaging has used a piezoelectric matrix array transducer with ultra-multiple elements, e.g., 1024 elements 32 , 33 .…”

An Accelerated Post-processing Calculation Method of Curved Surface Profile Extraction Based on the Total Focusing Method of Ultrasonic Phased Array

“…During the process, the ultrasonic waves pass through water-component double-layer medium. Surface extraction is an essential part to detect defects within components while applying TFM imaging of double-layer medium [12] [13]. Besides, it is important to extract the surface profile accurately in order to maintain a high image quality [14].…”

Remote, Volumetric Ultrasonic Imaging of Defects Using Two-Dimensional Laser Induced Phased Arrays

“…Additionally, real defects and structures are three dimensional such as in the case of cracking and inclusions in welds and can occur in arbitrary orientations. 2D arrays can generate volumetric images for better defect characterization than that can be achieved with a 1D array, due to the wider range of inspection angles [8,9].…”