Tunable negative refraction via acoustic grating-phononic crystal metamaterial in water

In underwater environments, controlling the propagation of acoustic waves faces complex physical challenges-especially under noisy conditions, variations in seawater density, and large-scale fluctuations in sound speed-that conventional acoustic techniques struggle to address effectively. This paper explores a novel research paradigm for achieving tunable negative refraction underwater. The proposed approach utilizes a metamaterial structure composed of a one-dimensional acoustic grating and a one-dimensional phononic crystal, offering a breakthrough theoretical scheme for tunable negative refraction of sound waves in aquatic settings. The paper begins by outlining the key issues in underwater acoustics research and the limitations of existing technologies, including challenges in underwater acoustic communication, imaging, and detection. It then provides an in-depth analysis of the fundamental structures of one-dimensional acoustic gratings and one-dimensional phononic crystals, detailing the mechanisms by which negative refraction is realized. Finally, the study investigates the tunability of the negative refraction phenomenon as dictated by the structural parameters.