Fan Xu-Dong, Liang Bin, Yang Jing, Cheng Jian-Chun
Collaborative Innovation Center of Advanced Microstructures and Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics, Department of Physics, Nanjing University, Nanjing, 210093, P. R. China.
National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi, 38677, USA.
Sci Rep. 2019 Feb 11;9(1):1750. doi: 10.1038/s41598-018-38424-3.
The past decade witnesses considerable efforts to design acoustic illusion cloak that produces the desired scattered field for a specific object illuminated by an external field. Yet the possibility of generating acoustic illusion directly for a sound source still remains unexplored despite the great fundamental and practical significance, and previous transformation acoustics-based designs need to have bulky sizes in terms of working wavelength. Here we propose to produce arbitrary illusion for an airborne sound source with no need to resort to coordinate transformation method. Based on an inherently different mechanism that uses acoustic metasurface to provide azimuthally-dependent local phase delay to the radiated wavefront, we shrink the thickness of the single layer enclosing the source to subwavelength scale without modulating the shape of layer. The performance of our scheme is demonstrated via distinct phenomena of virtually shifting the source location and introducing angular momentum. Numerical results verify our theoretical predictions, showing the extraordinary capability of the presented device to freely manipulate the radiation pattern of a simplest point source, making it acoustically appearing like another arbitrarily complicated source. Our findings open new avenues to the design and application of acoustic illusion devices and may have deep implications in many diverse fields such as architectural acoustics and biomedical engineering.
在过去十年中，人们付出了巨大努力来设计声学幻象斗篷，该斗篷能为外部场照射的特定物体产生所需的散射场。然而，尽管具有重大的基础和实际意义，但直接为声源产生声学幻象的可能性仍未得到探索，而且基于变换声学的先前设计在工作波长方面需要较大的尺寸。在此，我们提出无需借助坐标变换方法就能为空中声源产生任意幻象。基于一种本质上不同的机制，即利用声学超表面为辐射波前提供方位角相关的局部相位延迟，我们将包围声源的单层厚度缩小到亚波长尺度，而不改变层的形状。我们通过虚拟移动声源位置和引入角动量的独特现象展示了该方案的性能。数值结果验证了我们的理论预测，表明所提出的装置具有非凡的能力，可以自由操纵最简单点声源的辐射方向图，使其在声学上看起来像另一个任意复杂的声源。我们的发现为声学幻象装置的设计和应用开辟了新途径，并且可能在建筑声学和生物医学工程等许多不同领域产生深远影响。
