Quasi-flat high-index acoustic lens for 3D underwater ultrasound focusing

We report a quasi-flat and sub-wavelength acoustic lens built using soft matter process for broadband ultrasonic 3D focusing in water. By simple emulsion templating method, porous material with high index relative to water (∼5) has been molded shaped into convergent very low curvature thickness smaller than the working wavelength This kind of metasurface generates narrow focused beam, its focal length can be adjusted. These lenses may great interest underwater applications, where imaging are highly demanded.