S0兰姆波在渐变折射率声透镜中的聚焦

本文研究了S₀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S0波在不同声透镜内的传播，并与S₀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S₀兰姆波声透镜的设计提供了重要依据．

Focusing of the Lowest-Order Symmetric Lamb Wave in Gradient-Index Phononic Crystal Plate

In this work, the focalization of the lowest-order Lamb (S0) wave in the gradient-index phononic crystal plate or acoustic lens was investigated. Two kinds of acoustic lenses, namely ΓX or ΓM lenses respectively, were designed by adjusting the principal orientations ΓX or ΓM of phononic crystals relative to the propagation direction of incident waves. The numerical results obtained by the finite element method show good agreement with the theoretical results represented by the ray trajectories of S0 mode in the lenses computed by the geometrical formalism. It shows that the ΓX lens leads to a focal distance larger than its theoretical value while the ΓM lens leads to the contrary. Furthermore, the ΓX lens has a full width at half maximum (FWHM) smaller than the ΓM lens, and a maximum field intensity (MFI) larger than its ΓM counterpart. Both the numerical and theoretical results show that adjusting the principal orientation can effectively affect the characteristics of the focalization of S0 wave, which provides useful suggestions for designing future acoustic lenses.