A Study on the Influence of Wave Scattering in Metamaterial-Based Super-Resolution Imaging of Defects in Materials

Recently there is much interest in metamaterial based super resolution imaging. Several demonstrations have been reported using sources or slits as targets for imaging. However, in the context of non-destructive evaluation, imaging of defects and discontinuities within a sample are of more interest. Such defects, unlike sources or slits, induce wave scattering which could potentially impact image generation. This paper studies the effects of wave scattering by subwavelength spaced defects in holey structured metamaterial based super resolution imaging using numerical (finite element) models. In these models, the ultrasonic waves are assumed to impinge on the defects in a normal incidence through transmission configuration, and a line-scan image at the receiver location is generated based on the captured waves past the metamaterial. The influence of defect position within the specimen sample (object plane) and the receiver location (image plane) with respect to the metamaterial on the output images are investigated. The results show that the defect-induced wave scattering processes produce intensity and spatial artefacts that have a signature on imaging. For various parametric cases, the changes in the output images are quantified and discussed in the context of metamaterial based super resolution imaging in the field of non-destructive evaluation and non-invasive diagnostics.