Sound diffusion with spatiotemporally modulated acoustic metasurfaces

Traditional sound diffusers are quasi-random phase gratings attached to reflecting surfaces whose purpose is augment the spatiotemporal incoherence of acoustic field scattered from reflective surfaces. This configuration allows one cover a large surface by periodically tiling diffuser unit cells area while reducing undesirable specular reflection for incident plane waves. However, periodic arrangement leads coherent constructive and destructive interference in some directions which achieving diffusivity. The spatial uniformity energy conventional constructed this way fundamental limitation traditional approach not easily overcome when wishes In work, we investigate modulation admittance an as new improve diffusion. We develop semi-analytical model that employs Fourier series expansion determine consisting quadratic residue (QRD) design individual well admittances modulated with traveling wave frequency, $\omega_{\mrm{m}}$, amplitude, $Y_\mrm{m}$, wavenumber matches cell length, $\Lambda$. observe significant improvement diffusion performance due fact scatters into additional frequency--wavenumber pairs associated harmonics frequency their diffraction orders. results verified using time-domain finite element model.