Structured channel metalens (SCM) have excellent application in super resolution imaging. Several demonstrations have shown deep subwavelength imaging in both optics and acoustics using slits or sources as imaging targets and only in a through transmission configuration. However, in the context of Non-destructive Evaluation (NDE), imagining defects inside the sample close to the surface is of much interest. Also, in applications where access to both sides of the material is limited or impossible, such as in structural testing scenarios, pulse-echo becomes a more practical choice than through transmission technique. Hence, the extension of metamaterial concepts from research to productization has gained more attention recently.

This work presents a novel methodology to image defects inside samples using a narrow band conventional phased array probes to capture the amplified evanescent fields transmitted through the subwavelength features of SCM in both pulse-echo and through transmission modes. Simulations are performed to optimize the structured channel metalens. In finite element models, ultrasonic waves are assumed to impinge on the side drill holes (defects) in a normal incidence both in pulse-echo and through transmission configuration. A line-scan image at the receiver location is generated based on the captured waves according to the pitch of the conventional phased array probes past the metalens. The simulations are validated with experiments conducted in a similar fashion.