School of Mechanical and Aerospace Engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul, 151-744, Korea.
Institute of Advanced Machinery and Design, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul, 151-744, Korea.
Sci Rep. 2017 Aug 30;7(1):10072. doi: 10.1038/s41598-017-10691-6.
Conical refraction, which is quite well-known in electromagnetic waves, has not been explored well in elastic waves due to the lack of proper natural elastic media. Here, we propose and design a unique anisotropic elastic metamaterial slab that realizes conical refraction for horizontally incident longitudinal or transverse waves; the single-mode wave is split into two oblique coupled longitudinal-shear waves. As an interesting application, we carried out an experiment of parallel translation of an incident elastic wave system through the anisotropic metamaterial slab. The parallel translation can be useful for ultrasonic non-destructive testing of a system hidden by obstacles. While the parallel translation resembles light refraction through a parallel plate without angle deviation between entry and exit beams, this wave behavior cannot be achieved without the engineered metamaterial because an elastic wave incident upon a dissimilar medium is always split at different refraction angles into two different modes, longitudinal and shear.
锥形折射在电磁波中相当常见，但由于缺乏合适的天然弹性介质，在弹性波中尚未得到很好的研究。在这里，我们提出并设计了一种独特的各向异性弹性超材料板，它可以实现水平入射的纵波或横波的锥形折射；单模波分裂成两个斜向的耦合纵剪波。作为一个有趣的应用，我们通过各向异性超材料板进行了入射弹性波系统的平行平移实验。这种平行平移对于通过障碍物隐藏的系统的超声无损检测很有用。虽然这种波的行为类似于光线通过平行平板的折射，没有光束进出口之间的角度偏差，但如果没有工程化的超材料，这种波行为是无法实现的，因为弹性波入射到不同的介质中总是会以不同的折射角分裂成两种不同的模式，即纵波和剪切波。
