Tunable Metamaterial Lens for Ultra-Broadband Hydroacoustic Focusing

Acoustic metamaterial plays a vital role in underwater engineering applications. Here we present a novel tunable underwater metamaterial for ultra-broadband hydroacoustic focusing. The material consists of a soft matrix embedded with cavities that are surrounded by solid shells. The proposed design enables on-demand tuning of the effective acoustic parameters of the composite material through two independent regulation strategies, namely, (i) filling the cavities with different liquids, and (ii) stretching the soft matrix. We develop a theoretical framework for calculating the effective parameters of the material and validate it through finite element simulations and experiments. Our theoretical analysis indicates that the proposed material is able to achieve a widely tunable refraction index while maintaining a high transmission coefficient. In addition, a hydroacoustic focusing functionality is demonstrated using the proposed metamaterials. These findings set the stage for the development of next-generation hydroacoustic materials for underwater communication and acoustic imaging technologies.