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

Non-Destructive Testing (NDT) is an essential analysis technique used to evaluate an engineering component for internal discontinuities and defects without damaging the component. The principle of NDT is to transmit a high frequency mechanical energy, specifically high frequency sound waves into a component, followed by receiving and examining the subsequent signals on a test area of a component for detection of defects. The highest resolution of ultrasonic imaging produced is limited by half of its wavelength due to the scattering and absorption effect. The application of holey-structured metamaterial lens will be utilised to allow evanescent soundwaves and high frequencies to be amplified to overcome the image resolution limit. The aim of this Final Year Project is to investigate if using metamaterial lenses of different diameter than previous works available based on the author’s research, will improve the C-Scan image resolution, and determine the distance for defects of 4mm, 2mm, 1mm, 0.5mm, 0.4mm, 0.3mm and 0.2mm apart. A 4MHz transducer is used and the pulse-echo method is applied with the A-Scan machine to check for two distinct peaks representing the two actual defects found within Specimens 1 to Specimen 7. A 5MHz transducer is used and the immersion method is applied with the C-Scan machine to check whether the image resolution has improved and determine if the C-Scan machine can accurately detect the defects without and with the use of different lengths and diameters of the metamaterial lenses. Results show that metamaterial Lens 3 with D10L45mm produces the best image resolution when compared to without metamaterial lenses and with the metamaterial Lens 1, 2, 4 and 5. However, as the defect distance decreases to between 0.4mm to 0.2mm, the metamaterials lenses are unable to identify two defect holes. From defect distance of 0.4mm, the C-Scan is unable to distinguish the accurate defect distance apart. The results of the experiments, possible experimental errors, and suggestions for further improvement of this project will be discussed in this report.Bachelor of Engineering (Mechanical Engineering