Escalated deep-subwavelength acoustic imaging with field enhancement inside a metalens

• Main Authors: Chen, Jian, Sun, Zeqing, Rao, Jing, Lisevych, Danylo, Fan, Zheng
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Article
• Language: English
• Published: 2022
• Subjects: Engineering::Mechanical engineering; Superlens; Ultrasonography
• Online Access: https://hdl.handle.net/10356/154203
• Institution: Nanyang Technological University

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.