Broadband Characterization of Near-Field Focusing With Groove-Structured Lens

Subdiffraction focusing of acoustic waves in the near-field can remarkably improve the signal-to-noise ratio in super-resolution acoustic imaging. Recently, we have successfully demonstrated the feasibility of near-field focusing with groove-structured lens. However, as a very critical step toward practical applications, the broadband characterization of the near-field focusing lens remains unexplored. In this study, we numerically and experimentally characterize the broadband performance of the near-field lens for subdiffraction sound focusing. The simulated and measured results agree well, both of which confirm that the near-field focusing works well over broadband. Furthermore, we find that the range and symmetry of the working bandwidth were largely influenced by the profound effect of groove depth on the excitation of evanescent waves. This study aims to advance the practical applications of the simple ultracompact lens in various areas of acoustics.