Investigation on the use of metalens for ultrasound imaging in non-destructive testing

Abstract

Non-Destructive Testing (NDT) is a method used in many sectors to assess a material's, component's, or system's qualities without inflicting harm. This is especially helpful in sectors like manufacturing, aerospace, and medical, where it's necessary to evaluate a material's or component's integrity without jeopardizing their operation or safety. The scattering and absorption effect limits the greatest resolution of ultrasonic imaging to half of its wavelength. In order to surpass the image resolution limit, evanescent soundwaves and high frequencies will be amplified by the use of a holey-structured metamaterial lens created by the author. This final year project aims to investigate if the use of a lower frequency transducer as well as metamaterial lenses will help improve the image resolution and correctly determine the defect distance of 20mm, 10mm, 5mm, 4mm, 3mm and 1mm apart. A 0.5Mhz transducer is used for both experiments namely the Pulse-Echo method for A-Scan machine, as well as immersion testing for C-Scan machine to to check and identify for two distinct peaks which represents the two defects present on specimens 1 to 6. The experiment is conducted with and without the use of metamaterial lenses to check if metamaterial lenses can help with optimizing the image resolution as the defect distance gets closer. Results have shown that lens 1 with a diameter of 10mm and a length of 13.5mm produced the highest resolution factor which corresponded to the best image resolution for specimen 1 and 2. Lens 1 was also able to determine the defect distance accurately for both specimens. However, for specimen 3 to 6, as the defect distance decreases and gets closer with each other, the experiment yielded unsatisfactory results with and without the use of metamaterial lenses. With and without the use of metamaterial lenses, it was not able to produce two distinct peaks as well as determining defect distances accurately. This report will be discussing the experimental results, possible affecting factors/ experimental errors as well as possible further improvements to be made for this project.