A metamaterial ultrasound mode convertor for complete transformation of Lamb waves into shear horizontal waves

Yiran Tian; Yihao Song; Yanfeng Shen; Zhengyue Yu

doi:10.1016/j.ultras.2021.106627

A metamaterial ultrasound mode convertor for complete transformation of Lamb waves into shear horizontal waves

Ultrasonics. 2022 Feb:119:106627. doi: 10.1016/j.ultras.2021.106627. Epub 2021 Oct 19.

Authors

Yiran Tian¹, Yihao Song¹, Yanfeng Shen², Zhengyue Yu³

Affiliations

¹ University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China.
² 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. Electronic address: yanfeng.shen@sjtu.edu.cn.
³ Experimental Center of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai 200240, China.

PMID: 34688981
DOI: 10.1016/j.ultras.2021.106627

Abstract

This article reports a new mechanism involving a non-perforated resonant elastic metamaterial to achieve the complete conversion of Lamb waves (A₀ and S₀) into the fundamental shear horizontal (SH₀) 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 SH₀ 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.