论文标题
声音扩散与时空调制的声学杂音
Sound diffusion with spatiotemporally modulated acoustic metasurfaces
论文作者
论文摘要
传统的声音扩散器是与反射表面相连的准随机相光栅，其目的是增加从反射表面散射的声场的时空不一致。这种配置使人们可以通过定期铺设扩散器单位细胞来覆盖大型反射表面，以覆盖大面积，同时减少入射平面波的不良镜面反射。然而，单位细胞的周期排列会导致在某些方向上散布的场中的建设性和破坏性干扰，这对于实现声学扩散率是不希望的。以这种方式构建的传统扩散器散布的声能的空间均匀性是传统方法的基本限制，当人们希望覆盖大型反射表面时，不容易克服。在这项工作中，我们研究了声学扩散器表面声学的时空调制，作为改善声音扩散的新方法。 We develop a semi-analytical model that employs Fourier series expansion to determine the scattered sound field from a surface admittance consisting of a quadratic residue diffuser (QRD) design whose individual well admittances are modulated with a traveling wave with modulation frequency, $ω_{\mrm{m}}$, amplitude, $Y_\mrm{m}$, and a wavenumber that matches the unit cell长度，$λ$。我们观察到扩散性能的显着改善，这是因为时空调制散射到额外的频率中 - 与调制频率谐波及其衍射顺序相关的Wavenumber对。使用时域有限元模型对半分析模型结果进行验证。
Traditional sound diffusers are quasi-random phase gratings attached to reflecting surfaces whose purpose is to augment the spatiotemporal incoherence of the acoustic field scattered from reflective surfaces. This configuration allows one to cover a large reflecting surface by periodically tiling the diffuser unit cells to cover a large area while reducing undesirable specular reflection for incident plane waves. However, the periodic arrangement of the unit cells leads to coherent constructive and destructive interference in the scattered field in some directions which is undesirable for achieving acoustic diffusivity. The spatial uniformity of acoustic energy scattered from conventional diffusers constructed in this way is a fundamental limitation of the traditional approach which is not easily overcome when one wishes to cover large reflecting surfaces. In this work, we investigate spatiotemporal modulation of the surface acoustic admittance of an acoustic diffuser as a new approach to improve the sound diffusion. We develop a semi-analytical model that employs Fourier series expansion to determine the scattered sound field from a surface admittance consisting of a quadratic residue diffuser (QRD) design whose individual well admittances are modulated with a traveling wave with modulation frequency, $ω_{\mrm{m}}$, amplitude, $Y_\mrm{m}$, and a wavenumber that matches the unit cell length, $Λ$. We observe significant improvement in diffusion performance due to the fact that the spatiotemporal modulation scatters sound into additional frequency--wavenumber pairs associated with harmonics of the modulation frequency and their diffraction orders. The semi-analytical model results are verified using time-domain finite element model.
