Coding acoustic metasurfaces for tunable focusing in three-dimensional space

Acoustic focusing has been widely applied in biological and industrial fields. In this work, a coding acoustic metasurface consisting of two kinds of hexagonal coding bits is designed. Using the metasurface, acoustic focusing can be implemented in three-dimensional space. Besides, by altering the coding sequence, the focal length can be manipulated flexibly to satisfy the practical demands. Furthermore, bifocal focusing, which has a great potential in multiplane imaging, can be realized by properly arranging the coding sequence. Our works broaden the prospects of the coding metasurfaces and have promising applications in the areas of biomedical therapy and imaging.