In this project, we developed a 3D-printed gradient-index phononic crystal based on air inclusions in a polymer to manipulate underwater acoustic waves. The proposed approach enables a simple configuration without heavy inclusions or geometrically complex unit cells to create a refractive-index profile based on Luneburg lens. The goal was to focus incident acoustic plane waves propagating in a known direction as shown in the animation.
Based on the band-structure analysis, we designed, 3D-printed, and tested gradient-index lens yielding an excellent agreement between the experimental results and finite-element simulations of underwater acoustic wave focusing. The animation shows an incident acoustic pressure pulse when the lens is present versus without it. The experimental focusing is also compared to numerical time domain simulations using COMSOL.
The phononic crystal concept and the resulting lens design can find applications spanning from power enhancement in acoustic energy transfer and harvesting to signal enhancement in sensing and imaging.