Annular acoustic impedance metasurfaces for encrypted information storage

Extensive research has been devoted recently to the design of metasurfaces. Design strategies based on impedance theory stand out for power-flow regulation. The designed impedance matrix is characteristic of a given pair of incident and modulated wave fields, hence providing opportunities for encrypted information storage. We consider acoustic vortices propagating along a cylindrical shell waveguide as signal carriers. Within the shell waveguide, an annular acoustic impedance metasurface is introduced for encrypted information storage. Information stored in the metasurface would only be retrieved when interrogated with the correct input. Hidden messages are successfully read in numerical simulation when the three-layer model is used to implement the metasurface. A realistic structure based on Helmholtz resonant unit cells is further designed to verify experimentally the encryption storage process. This work is expected to spur more applications of impedance metasurface to acoustic holography and encrypted acoustic communications.