Poroelastic microlattices for underwater wave focusing

Architected materials consisting of open cell structures with microscale beam elements, i.e., microlattices, have demonstrated unprecedented quasi-static mechanical response and tailorable acoustic properties. When microlattices are coupled with pressure waves, the interplay between elastic waves in solid medium and pressure waves in surrounding fluid can be explained in the context of Biot theory. In this work, we characterize the acoustic properties of fluid-saturated elastic lattices under long wavelength approximation both numerically and experimentally. A Luneburg lens with modified index profile adapted for underwater wave focusing is demonstrated via the finite element analysis. We experimentally validate this design by 3D printing a gradient-index lens consisting of octet trusses with a spatially varying beam radius. Our method showcases a computationally efficient homogenization design approach that enables accelerated design of acoustic wave manipulation devices. By matching the acoustic impedance with surrounding fluid, microlattices with extraordinary stiffness-to-density ratio and enhanced transmission will prove useful for biomedical applications.