Tian Yiran, Song Yihao, Shen Yanfeng, Yu Zhengyue
University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China.
University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Key Laboratory for Digital Maintenance of Buildings and Infrastructure, Shanghai 200240, China.
Ultrasonics. 2022 Feb;119:106627. doi: 10.1016/j.ultras.2021.106627. Epub 2021 Oct 19.
This article reports a new mechanism involving a non-perforated resonant elastic metamaterial to achieve the complete conversion of Lamb waves (A and S) into the fundamental shear horizontal (SH) wave. The proposed metamaterial ultrasound mode convertor is studied via the observation of the special resonant shear motion of its unit cells, initiating with a conventional additive stub design. Thereafter, such a stubbed structure is further modified to fully couple the Lamb modes with the shear horizontal stub motion. By investigating the band structure of the metamaterial unit cell through modal analysis and tuning the shear resonant motions, a complete SH mode generation band within the simultaneous Lamb modes bandgap can be established in a wide frequency range. Such a special bandgap situation enables the complete mode conversion from Lamb waves into shear horizontal waves. The transformation capability of the proposed ultrasound mode convertor is further substantiated via the harmonic analysis of metamaterial chain model, showcasing the frequency spectrum of the transmitted wave modes. The optimal configuration is determined by conducting a parametric study to identify the most effective mode conversion performance. Finally, a coupled-field transient finite element simulation is carried out to acquire the dynamic response of the structure. The frequency-wavenumber analysis of the transmitted wave field illuminates the successful realization of the mode conversion behavior. Experimental demonstrations are presented to validate the numerical predictions. The proposed complete mode conversion capability may possess great potential for wave control and manipulation.
本文报道了一种新机制，该机制涉及一种无穿孔的共振弹性超材料，以实现兰姆波（A波和S波）到基本水平剪切（SH）波的完全转换。通过观察其单元胞的特殊共振剪切运动，从传统的附加短截线设计开始，对所提出的超材料超声模式转换器进行了研究。此后，对这种带短截线的结构进行进一步修改，以使兰姆模式与水平剪切短截线运动完全耦合。通过模态分析研究超材料单元胞的能带结构并调整剪切共振运动，可在较宽的频率范围内，在同时存在的兰姆模式带隙内建立完整的SH模式产生带。这种特殊的带隙情况能够实现从兰姆波到水平剪切波的完全模式转换。通过对超材料链模型的谐波分析进一步证实了所提出的超声模式转换器的转换能力，展示了透射波模式的频谱。通过进行参数研究以确定最有效的模式转换性能，从而确定了最佳配置。最后，进行了耦合场瞬态有限元模拟，以获取结构的动态响应。对透射波场的频率 - 波数分析表明成功实现了模式转换行为。给出了实验演示以验证数值预测。所提出的完全模式转换能力可能在波的控制和操纵方面具有巨大潜力。
