Fig. 5: Applications of transmissive metasurfaces.

a | The principle of a metasurface for asymmetric transmission. b | The measured transmitted sound fields show asymmetric transmission. The acoustic fields of the negative direction (left) and positive direction (right) are shown. A photo of a prototype of an asymmetrical transmissive metasurface is also shown (lower). c | The top panel indicates that the phase distribution shown will produce a letter A at the image plane. The simulation and experimental results at different planes (middle and bottom panels, respectively). The letter A can be seen on the image plane. d | A schematic of the metasurface with eight sections assigned with different phase shifts. The vortex sound field produced from the metasurface shows spiral phases. θ, rotation angle of metasurface relative to the original position; λ, wavelength; ASA, angular spectrum approach. Panel a is adapted with permission from ref.²⁷, AIP. Panel b is adapted with permission from ref.³², APS. Panel c is adapted from ref.⁹², Springer Nature Limited. Panel d is adapted with permission from ref.²⁹, APS.