Acoustic reprogrammable metasurface for the multi-frequency tri-channel retroreflector

Here, we propose a reprogrammable reflection-type AM. By incorporating an external water pumping system into the unit cell of the AM, the scattering state of each individual unit cell can be tailored by employing different pumped water volumes. To validate the performance of the proposed AM, the tri-channel retroreflector with specific retro-reflection angles is designed at three frequencies of interest. The quasi-retroreflection can be realized when the sound with other incident angles impinges on the retroreflector and the theoretical value of the quasi-retro-reflection angle can also be concluded. The reflected sound pressure field and the polar directivity pattern are computed based on the finite element method. Our proof-of-concept simulations agree well with theoretical predictions, showing that the multi-frequency retroreflector based on the reprogrammable AM has the capability of realizing the tri-channel retroreflection and the quasi-retroreflection.