A 3D-printed gradient-index phononic crystal structure based on air inclusions in a polymer is introduced to manipulate underwater acoustic waves. The proposed approach enables a simple configuration without heavy inclusions or geometrically complex unit cells to create the required refractive-index profile and focus incident plane waves propagating in a known direction. Based on the band-structure analysis, a gradient-index lens is designed, fabricated, and tested, yielding an excellent agreement between the experimental results and finite-element simulations of underwater acoustic wave focusing. The proposed concept and the resulting lens design can find applications spanning from power enhancement in acoustic energy transfer and harvesting to signal enhancement in sensing and imaging.

中文翻译：

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用于水下声波聚焦的3D打印梯度折射率声子晶体透镜

引入了基于聚合物中空气夹杂物的3D打印梯度指数声子晶体结构，以操纵水下声波。所提出的方法使得能够进行简单的配置而无需大量的夹杂物或几何形状复杂的晶胞来产生所需的折射率分布并聚焦在已知方向上传播的入射平面波。基于能带结构分析，设计，制造和测试了一种梯度折射率透镜，在实验结果与水下声波聚焦的有限元模拟之间取得了很好的一致性。提出的概念和最终的透镜设计可以找到从声能传输和收集中的功率增强到感测和成像中信号增强的应用。