Metamaterial-assisted acoustic manipulation of large objects in water

Metamaterials are engineered structures that exhibit unprecedented wave-structure interactions. Recently, acoustic metamaterials were applied to reshape acoustic radiation force and assist remote manipulation of large objects (i.e., objects greater than at least twice the wavelength) in air. However, metamaterial-assisted acoustic manipulation has not been demonstrated in water before. A key challenge is the limited availability of material types and fabrication methods to create underwater metamaterials with sufficient acoustic impedance contrast with water and high-resolution structure patterns. To address that, we developed a new type of underwater metamaterial based on soft lithography of a metal-resin composite. Using the new metamaterial, we demonstrated the manipulation of objects greater than 20 times the acoustic wavelength in water. We designed metamaterial patches that enable various manipulation functions such as “pushing,” “following,” and “rotating,” and integrated multiple functions into a single patch based on surface pattern superimposition and frequency multiplexing. Based on these fundamental functions, we further demonstrated more complex multi-object, multi-path, non-invasive, and 3-D underwater object manipulation. Our metamaterial-assisted remote underwater acoustic manipulation presents future opportunities for advancing underwater robot actuation, vehicle transportation, manufacturing, as well as drug delivery and minimally invasive surgery.