Figure 4

Planar acoustic lens constructed by an acoustic metasurfaces.

(a) Schematic diagram of the design of lens. A hyperboloidal phase profile along y direction is utilized to focus acoustic plane wave to a single point at a distance f from the metasurfaces. The green spherical line with radius f is the desired equiphase surface of the reflected wave so that the phase shift at should be proportional to the length of the red line . The theoretical continuous phase shifts (red dots) and the discrete phase shifts provided by the metasurfaces (blue squares) along the y direction are shown in (b). The half-height of the lens is chosen to be 80 cm. (c) Spatial distribution of the intensity field for the designed lens with f = 3λ. (d) Transverse cross-section of intensity profile at x = 63 cm for the designed lens. The black dash line refers to the intensity of the incident waves.