Underwater sound focusing via quasi-three-dimensional gradient-index lens
Phys. Rev. Applied 23, 064057 – Published 25 June, 2025
DOI: https://doi.org/10.1103/5z2y-d2c3
Abstract
Gradient-index lenses, enabled by meta-atoms, have demonstrated effective focusing capabilities in both airborne and submerged environments. However, the current focusing capabilities remain constrained primarily to two-dimensional systems. Here we introduce a quasi-3D gradient-index lens designed for underwater sound focusing. This lens, characterized by a simple yet effective design, features an additional degree of freedom along the axial direction, enabling controlled wave refraction in longitudinal and lateral directions. To achieve this, eigenfrequency analysis and a scattering parameter retrieval method are used to calculate the band structure and characterize the effective material properties. Numerical simulations and experimental validation confirm the efficacy of the lens in focusing underwater sound and highlight its potential for high-resolution sensing, advanced biomedical imaging, and efficient energy harvesting.
