Mass-stiffness substructuring of an elastic metasurface for full transmission beam steering
Mass-stiffness substructuring of an elastic metasurface for full transmission beam steering
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DOI：
10.1016/j.jmps.2017.11.025
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发表时间：
2018-03-01
影响因子：
5.3
通讯作者：
Kim, Yoon Young
中科院分区：
文献类型：
--
作者：
Lee, Hyuk;Lee, Jun Kyu;Kim, Yoon Young
超表面概念因其新颖的波前整形功能而具有巨大的潜力，对于基于超声波和固体波的应用至关重要。为了实现所需的功能，弹性超表面应覆盖完整的 2 pi 相移，并在亚波长范围内获得完全传输。然而，它们在弹性状态方面还没有得到太多的探索，因为连续弹性介质内质量刚度的固有比例导致了突然相移和充分传输之间不可避免的权衡。我们的目标是设计一种弹性超表面，它可以实现（放大的）有效质量和（减弱的）刚度之间的反比关系，以满足完整的 2 pi 相移以及完整的传输。为了实现这一目标，我们提出了一种连续弹性超表面晶胞，它被分解为两个子结构，即具有局部偶极谐振器的质量调谐子结构和由非谐振多孔狭缝组成的刚度调谐子结构。我们通过分析、数值和实验证明，这种独特的子结构晶胞可以满足高传输所需的相移。底层结构可以在很宽的值范围内独立调整弹性属性。我们使用所提出的连续体晶胞的质量弹簧模型来研究所提出的超表面的工作机制。通过设计的由嵌入铝板的子结构单元组成的超表面，我们证明了我们的超表面可以成功实现面内纵向超声波束的反常转向和聚焦。所提出的子结构概念有望为通用弹性超表面的设计提供新原理，可用于有效地设计任意波剖面。 (C) 2018 Elsevier Ltd. 保留所有权利。
The metasurface concept has a significant potential due to its novel wavefront-shaping functionalities that can be critically useful for ultrasonic and solid wave-based applications. To achieve the desired functionalities, elastic metasurfaces should cover full 2 pi phase shift and also acquire full transmission within subwavelength scale. However, they have not been explored much with respect to the elastic regime, because the intrinsic proportionality of mass-stiffness within the continuum elastic media causes an inevitable trade-off between abrupt phase shift and sufficient transmission. Our goal is to engineer an elastic metasurface that can realize an inverse relation between (amplified) effective mass and (weakened) stiffness in order to satisfy full 2 pi phase shift as well as full transmission. To achieve this goal, we propose a continuum elastic metasurface unit cell that is decomposed into two substructures, namely a mass-tuning substructure with a local dipolar resonator and a stiffness-tuning substructure composed of non-resonant multiply-perforated slits. We demonstrate analytically, numerically, and experimentally that this unique substructured unit cell can satisfy the required phase shift with high transmission. The substructuring enables independent tuning of the elastic properties over a wide range of values. We use a mass-spring model of the proposed continuum unit cell to investigate the working mechanism of the proposed metasurface. With the designed metasurface consisting of substructured unit cells embedded in an aluminum plate, we demonstrate that our meta surface can successfully realize anomalous steering and focusing of in-plane longitudinal ultrasonic beams. The proposed substructuring concept is expected to provide a new principle for the design of general elastic metasurfaces that can be used to efficiently engineer arbitrary wave profiles. (C) 2018 Elsevier Ltd. All rights reserved.