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. 2021 Jul 12;11:14322. doi: 10.1038/s41598-021-93812-6

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© The Author(s) 2021

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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The schematics of (a) the virtual space, (b) the intermediate space and its refractive index, and (c) the physical space and its refractive index. The constant $η$ and $ξ$ coordinate lines in the intermediate space and their corresponding mapped images in the virtual and physical spaces are depicted by black and red lines, respectively.