An ultrathin planar acoustic metasurface diffuser with narrowband uniform reflection

Diffuse reflection of sound is desirable in many practical scenarios, such as architectural acoustics, but most existing designs of acoustic diffusers have bulky size, corrugated profile, or limited spatial resolution. We design an ultrathin planar acoustic diffuser for producing narrowband diffuse reflection with high uniformity via precise modulation of reflected wavefront and propose a metasurface-based implementation comprising a monolayer of Helmholtz-like resonators much smaller than the working wavelength in all three dimensions. Our design is benchmarked with a commercialized Schroeder diffuser and is numerically proven to be capable of scattering the illuminating wave more uniformly than the conventional mechanisms based on the quadratic residue sequence over wide incident angles. We anticipate our design with simplicity and capability to find important applications in diverse scenarios.