Novel Diverging Acoustic Lens Geometries for Row-Column Array Transducers

Double-curved diverging lenses are used to extend the Field of View (FOV) of flat 2D Row-Column Addressed (RCA) transducers, for performing real-time volumetric imaging of large organs. Such lenses are usually made in a spherical shape geometry, which poorly fits the square footprint of RCA arrays. In particular, for large arrays, the radius of curvature of the lens is constrained to increase significantly for the lens to cover the whole array. However, a large radius of curvature directly decreases the diverging efficiency of a lens. We hypothesize that novel acoustic lenses geometries can be designed to optimize the FOV of large RCA. In this work, the proposed Steinmetz and Bicylindrica lenses provide a full array coverage, while maintaining a small radius of curvature and thickness. These lenses have been fabricated in Polymethyl methacrylate (PMMA) and mounted on a 25.6 mm² 128+128 RCA Vermon transducer. The FOV of the 4 mm thick lenses has been measured and results in an increase from 14.6^◦ for a spherical lens to 24.1^◦ for a Steinmetz lens and 29.0^◦ for a Bicylindrical lens. The transmit pressure fields and wire phantom images are also presented and prove the viability of these new thin lens designs. This work shows that the new geometries are suitable for fabricating efficient diverging lenses for large 2D RCA transducers. These lenses are highly desired for achieving 3D imaging of large organs.