Acoustic metalens with switchable and sharp focusing

Abstract Sharp and tunable focusing functionality is highly desired in various acoustic application fields. Here, we propose a simply structured metalens for water-borne sounds with a switchable focusing functionality. Each meta-atom in the lens is composed of two elliptical iron cylinders, and is smartly designed so that it can redirect a normally incident plane wave toward the same focal spot. A switchable focusing functionality between a transmissive lens and a reflective one can be achieved by simply rotating the elliptical cylinders. Furthermore, a sharp focusing effect is obtained with a high-intensity concentration ratio along both transverse and longitudinal directions.