Poroelastic microlattices for underwater wave focusing

Metamaterials with microscale architectures, e.g., microlattices, can exhibit extreme quasi-static mechanical response and tailorable acoustic properties. When coupled with pressure waves in surrounding fluid, the dynamic behavior of microlattices in the long wavelength limit can be explained in the context of Biot's theory of poroelasticity. In this work, we exploit the elastoacoustic wave propagation within 3D-printed polymeric microlattices to incorporate a gradient of refractive index for underwater ultrasonic lensing. Experimentally and numerically derived dispersion curves allow the characterization of acoustic properties of a fluid-saturated elastic lattice. A modified Luneburg lens index profile adapted for underwater wave focusing is demonstrated via the finite element method and immersion testing, showcasing a computationally efficient poroelasticity-based design approach that enables accelerated design of acoustic wave manipulation devices. Our approach can be applied to the design of acoustic metamaterials for biomedical applications featuring focused ultrasound.