Modulation of acoustic waves by a broadband metagrating.

Metasurface has recently attracted a lot of attentions for controlling wave fields. Based on the diffraction effects of phase gratings, we demonstrate a broadband acoustic metagrating which can concentrate the diffracted waves in the first (±1) orders and achieve multifunctional wave steering such as broadband anomalous diffraction. In the acoustic metagrating, the subwavelength rectangular waveguides (SRWs) function as the periodic elements to replace the fences in ordinary gratings. Thus, we can achieve a group of phase delay from 0 to 2π independently with frequency just by reconfiguring the relative locations of the effective apertures. With the iterative algorithm, the acoustic metagrating can be used to record the phase profile and then control the output waveform. We further demonstrate that the broadband metagrating can be used to achieve the acoustic Gaussian beam. By rotating the periodic elements into a two-dimensional structure, the Bessel beam is further obtained.