4.6 Article

Broadband and high-numerical-aperture sharp focusing for waterborne sound with metagrating-based lens

Journal

NEW JOURNAL OF PHYSICS
Volume 24, Issue 9, Pages -

Publisher

IOP Publishing Ltd
DOI: 10.1088/1367-2630/ac8e27

Keywords

metagrating; super-resolution metalens; broadband focusing; sub-diffraction focusing

Funding

  1. Guangdong Province Key Research & Development Program [2020B0404010001]
  2. Guangdong Basic and Applied Basic Research Foundation [2021A1515010322]

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In this study, we design and demonstrate a metagrating-based lens that achieves broadband and high-numerical-aperture focusing for waterborne sound. Numerical simulations show that the lens has sharp and efficient sound wave focusing, surpassing the Rayleigh-Abbe diffraction limit.
Metalens with broadband and high-efficiency focusing functionality is desired in various underwater acoustic applications such as sonar and oceanography. Here we design and demonstrate a metagrating-based lens consisting of spatially sparse and wavelength-scale meta-atoms with optimized structures. With the help of grating diffraction analysis and intelligent optimization algorithm, the reflective metalens enables broadband and high-numerical-aperture focusing for waterborne sound over a 40 kHz-bandwidth for working frequency at 200 kHz. Full-wave numerical simulations unambiguously verify a sharp and high-efficiency focusing of sound wave intensity, with the full width at half maximum at the focal spot being smaller than 0.5 lambda and thus beating the Rayleigh-Abbe diffraction limit. Our work not only provides an intelligent design paradigm of high-performance metalens, but also presents a potential solution for the development of planar acoustic devices for high-resolution applications.

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