Transmodal elastic metasurface for broad angle total mode conversion

Abstract

It has been long believed that a total mode conversion between longitudinal and shear elastic waves can only be achieved at a certain incidence angle. Here, we show that a total mode conversion can be achieved for a broad range of incidence angles by a specially designed elastic metasurface, namely, transmodal metasurface. From the generalized reflection law, we found that the incident longitudinal wave can be totally converted to a reflected shear wave over a broad range of incidence angles if a sufficiently large phase gradient is introduced at the boundary. Numerical and experimental investigations with a specially engineered transmodal metasurface showed that the total mode conversion can be achieved for wide incidence angles from 19° to 90°, which was impossible to be achieved previously. The proposed idea of the transmodal metasurface can open up an advanced avenue for tailoring elastic wave modes as an outstanding alternative to generating shear waves.

Tunable multifunctional fish-bone elastic metasurface for the wavefront manipulation of the transmitted in-plane waves

“…From the nephograms of the phase shift for the transmitted P-and SV-waves, as shown in Figs. 3(a) and 4(a), it can be found that the phase shift indeed has a full 2π coverage in a wide frequency range (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)). The corresponding wavelengths for the P-and SV-waves are 191 -127 mm and 111 -74 mm, respectively.…”

“…Furthermore, some works have reported on manipulating in-plane P-and SV-waves simultaneously, e.g. splitting of P-wave and SV-wave [35,36], converting P-wave to SV-wave [37] and manipulating multimodal ultrasonic guided waves [38]. Recently, topology optimization has been used to manipulate longitudinal and shear waves [39].…”

Advances in the study of elastic metasurfaces

“…揭示了 单胞间有利耦合和不利耦合的内部机理, 并指出由于 聚焦型超构表面连续的相位变化使得所有相邻单胞间 图 8 (网络版彩图) (a) 无序弹性波超构表面 [115] ; (b) 非局部弹性波超构表面 转换只能在一定的入射角下产生. Kim等人 [83] 通过在 板结构边界设计平均长度约为P波波长一半的梯度波 导谐振子, 构成亚波长反射型超构表面, 实现了板结构 中入射P波在19°~90°的大入射角范围内, 全部模式转 换为剪切SV波, 为结构健康监测信号处理技术提供了 新的思路. 本文作者 [84] 也成功地将亚波长的弹性波超 (1) 随着研究工作的深入, 研究人员发现广义斯涅 尔定律对解释一些涉及高阶衍射的新现象不再有效, 如入射角超过所谓的临界角 [135,136] 和一些不被期望的 泄漏波 [48,74] .…”

Steering Flexural Waves by Amplitude-Shift Elastic Metasurfaces

“…In light of that, the elastic metasurface has been recently developed to offer a preferable possibility to manipulate elastic waves (Zhu and Semperlotti, 2016;Kim et al, 2018;Su et al, 2018). Compared with metamaterials, metasurfaces are compact in size, easier to fabricate and with smaller losses (Liu et al, 2017;Li et al, 2018), because they only consist of single-or few-layer unit cells, to shape discontinuous physical fields between different regions (Chen et al, 2016;Assouar et al, 2018).…”