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

Abstract

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