Twisting acoustic reflections by spiral sound diffusers

Abstract

We report broadband metasurfaces to control sound diffusion in the far field by the scattering of acoustic vortices. By encoding the holographic field of an acoustical vortex, these metasurfaces result in structures with spiral geometry. These metasurfaces inhibit specular reflections in the far field because all scattered waves interfere destructively in the normal direction. The scattering function is then unusually uniform because the reflected waves diverge spherically from the holographic focal spot. By triggering vorticity, energy can be evenly reflected in all directions except to the normal and, consequently, we observe a mean correlation-scattering coefficient of 0.99 (0.98 in experiments) and a mean normalized diffusion coefficient of 0.73 (0.76 in experiments) over a 4-octave frequency band. These spiral metasurfaces are good candidates to generate diffuse sound reflections for room acoustics, underwater acoustics, biomedical ultrasound, or particle manipulation devices.

@inproceedings{JimenezINTERNOISE2021a,
 author = {Noé Jiménez and Jean-Philippe Groby and Vicent Romero-García},
 booktitle = {EuroNoise 2021: European Congress and Exposition on Noise Control Engineering. Madeira, Portugal. 24-27 October},
 doi = {http://www.sea-acustica.es/},
 editor = {Conference proceedings},
 month = {10},
 organization = {Sociedade Portuguesa de Acústica},
 pages = {1271-1274},
 series = {Oral},
 title = {Twisting acoustic reflections by spiral sound diffusers},
 url = {http://www.sea-acustica.es/},
 year = {2021}
}