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本文研究了S_0兰姆波在渐变折射率声子晶体中的聚焦现象.通过调整正方晶格声子晶体的主轴方向与波传播的相对方向,设计了ΓX和ΓM方向两组不同的渐变折射率声透镜.采用有限单元法模拟S_0波在不同声透镜内的传播,并与S_0波在声透镜内的传播迹线做了对比,数值结果和理论结果基本一致.数值计算结果显示:ΓX方向的声透镜的焦距fl略大于其理论值,而ΓM方向的声透镜的fl则略小于其理论值.ΓX方向的声透镜的横向分辨率FWHM小于ΓM方向的声透镜,而聚焦强度MFI则大于ΓM方向的声透镜.结果表明,通过调整声子晶体的主轴方向与波传播的相对方向,可以显著地改变声透镜的聚焦特征.这为S_0兰姆波声透镜的设计提供了重要依据.
In this paper, the focusing phenomenon of S_0 Lamb waves in graded-index phononic crystals is studied. By adjusting the principal directions of the square lattice phononic crystals and the relative directions of the wave propagation, two different graded-refractive indices of ΓX and ΓM directions are designed Acoustic lens.The finite element method was used to simulate the propagation of S_0 wave in different acoustic lenses and compared with the propagation traces of S_0 wave in the acoustic lens.The numerical results were basically consistent with the theoretical results.The numerical results show that the ΓX direction The focal length of the acoustic lens fl is slightly larger than its theoretical value, while the fl of the acoustic lens in the ΓM direction is slightly smaller than its theoretical value. The lateral resolution FWHM of the acoustic lens in the direction of ΓXX is smaller than the acoustic lens in the ΓM direction while the focusing intensity MFI is greater than ΓM The results show that the focus characteristics of the acoustic lens can be significantly changed by adjusting the principal direction of the phonon crystal and the relative direction of the wave propagation, which provides an important basis for the design of the S_0 Lamb wave acoustic lens.