This letter describes a theoretical and experimental study of an underwater acoustic Luneburg lens made of isotropic metamaterial. The designed lens is found to be capable of focusing plane waves over a broad range from 160 to 210 kHz. The measured lateral width of the focal spot is 5.5 mm, an ideal size that is close to the Rayleigh resolution limit. The functionality of the underwater lens is realized by an artificial structure. Different from those rigid-scatterers-based devices, the working mechanism of the proposed structure is by introducing waterborne ultrasound waves into the solid structures and manipulating mechanical waves.

中文翻译：

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晶格水下Luneburg声透镜

这封信描述了由各向同性超材料制成的水下Luneburg声学透镜的理论和实验研究。发现设计的透镜能够聚焦平面波，频率范围从160到210 kHz。测得的焦点横向宽度为5.5 mm，这是一个理想尺寸，接近瑞利分辨率极限。水下镜头的功能是通过人工结构实现的。与那些基于刚性散射体的设备不同，该结构的工作机制是将水性超声波引入固体结构并操纵机械波。