Focusing of water waves with a shallow-draft cylinder array

The propagation of water waves can be manipulated via artificial structures. However, such structures usually need to possess a large volume ratio in water, and it may not be easy to build and move them in practical ocean engineering. Here, we theoretically propose and experimentally demonstrate a fixed, shallow-draft cylinder array that can refract and focus water waves within a wide range of wavelengths. When impinging upon the cylinder array from a region of water without structures, water waves can be slightly reflected at the surface of the array and speeded up in the array. As a result, favorable focusing performances such as a short focal length and high intensity at the focal point are observed.