High-order acoustic vortex field generation based on a metasurface.

In this paper, we generalize the principle of a generated first-order acoustic vortex (AV) with the acoustic resonances (AR) of a metasurface, from which we have also proposed a method for generating the higher-order AVs by arranging the sequences of the AR metasurface properly. The usable frequency range of the designed AR metasurface has been investigated and is discussed in detail, which is about 4470-4600Hz and covers the range 0.977-1.006f (f=4573.31Hz is the preset working frequency) approximately. Meanwhile, the designed AR metasurface can produce a frequency-adjustable AV field efficiently by adjusting the structure size and parameters of the planar AR layer. By discretizing the continuous phase distribution, the multiplexed AV beam with multiple orbital angular momentum states can also be generated effectively by arranging AR metasurface properly. The generated single and multiplexed AV beams can also be detected with the aid of the acoustic reverse phase plates accordingly.