Escalated Deep-Subwavelength Acoustic Imaging with Field Enhancement Inside a Metalens

Super-resolution acoustic imaging with state-of-the-art spatial resolution (lambda/50), with lambda being the wavelength, is showcased with a holey-structured metalens. However, the imaging mechanism under unity transmission based on Fabry-Perot resonances means the metalens fundamentally suffers from narrow bandwidth and limited deep-subwavelength contrast, and therefore further advancement of deepsubwavelength imaging has been stalled. Here we break the barriers for deep-subwavelength acoustic imaging comprehensively in spatial resolution, resolving contrast, and working bandwidth, by exploiting field enhancement inside the metalens. A microscopic model is established to theoretically reveal the underlying physics for escalated deep-subwavelength acoustic imaging. For a proof-of-concept, the imaging performance of the proposed method is numerically proven and experimentally demonstrated. Specifically, a breakthrough resolution below lambda/100 is achieved while resolving contrast is improved by at least 6.5 times and working bandwidth is broadened to approximately 25% of the operating frequency. Furthermore, pulsed acoustic imaging on the deep-subwavelength scale is showcased, which is an important step towards the practical application of the ultrahigh-resolution acoustic imaging technique. We believe the work presented here may greatly benefit a variety of fields in acoustics, such as visualizing subcutaneous structures in medical diagnosis and characterizing subsurface flaws in industrial nondestructive evaluation.

Automated summary

By exploiting field enhancement inside the metalens, breakthrough deep-subwavelength acoustic imaging is achieved with improved resolution, contrast, and working bandwidth. This method has the potential to greatly benefit various fields such as medical diagnosis and industrial nondestructive evaluation.