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. 2018 Apr 12;8:5906. doi: 10.1038/s41598-018-24231-3

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© The Author(s) 2018

Open Access This 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 license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license 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 license, visit http://creativecommons.org/licenses/by/4.0/.

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The reflection phases of the designed unit cells, sound absorption coefficients of the whole structure covered by the dark skin and pressure field distributions. (A) The reflection phases of the designed cells with pre-designed phase shifts at 1400 Hz. (B) The sound absorption coefficients of the whole dark skin covered structure when an incoming sound plane wave perpendicularly (90 deg) and obliquely (45 deg) illuminate the structure. Pressure field distributions when an incoming sound plane wave illuminate bare object (up row) and dark skin-covered object (down row) at 800 Hz (C), 1400 Hz (D), 3000 Hz (E), 4000 Hz (F), and 6000 Hz (G).