Wavelength-dependent multi-functional wavefront manipulation for reflected acoustic waves

We propose the design of an ultrathin planar acoustic metasurface with wavelength-dependent manipulation of a reflected wave. The metasurface comprises meta-atoms composed of multiple resonant elements working collectively to produce desired phase responses at different frequencies. We numerically demonstrate the performance of the proposed device via distinctive examples of achromatic acoustic convergence, and production of anomalous reflection, sound focusing and diffuse reflection at three prescribed frequencies. Our design opens an avenue to novel multi-functional acoustic devices and may find applications in diverse practical scenarios requiring independent wavefront manipulation at different frequencies such as information multiplexing/demultiplexing and architectural acoustics.