Abstract
“Schroeder diffuser” is a classical design, proposed over 40 years ago, for artificially creating optimal and predictable sound diffuse reflection. It has been widely adopted in architectural acoustics, and it has also shown substantial potential in noise control, ultrasound imaging, microparticle manipulation et al. The conventional Schroeder diffuser, however, has a considerable thickness on the order of one wavelength, severely impeding its applications for low-frequency sound. In this paper, a new class of ultrathin and planar Schroeder diffusers are proposed based on the concept of an acoustic metasurface. Both numerical and experimental results demonstrate satisfactory sound diffuse reflection produced from the metasurface-based Schroeder diffuser despite it being approximately 1 order of magnitude thinner than the conventional one. The proposed design not only offers promising building blocks with great potential to profoundly impact architectural acoustics and related fields, but it also constitutes a major step towards real-world applications of acoustic metasurfaces.
- Received 9 December 2016
DOI:https://doi.org/10.1103/PhysRevX.7.021034
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Sound diffusers help improve the perception of sound in a room—such as improving the clarity of speech or reducing ambient noise—by dispersing sound waves or favoring specific reflections. Traditional sound diffusers, known as Schroeder diffusers, have enjoyed great success, but their bulky size limits their usefulness. They are not practical for low- to mid-frequency sound, a fundamental limitation that has been well known for over 40 years. One possible solution relies on metasurfaces, ultrathin materials composed of building blocks that work together to create novel properties. Although acoustic metasurfaces have been actively studied, their potential for diffuser reflection is largely unexplored. We have designed and implemented the first metasurface-based sound diffuser, which performs on par with conventional diffusers despite being roughly one-tenth as thick.
Our design lays out ultrathin square cavities with different neck widths, chosen to induce phase shifts in incident sound waves at the design frequency. We benchmarked the design using numerical simulations and experiments with a prototype, created from 3D-printed acrylonitrile-butadiene-styrene plastics. By mapping the far-field scattering patterns as well as the near-field scattered pressure fields, we found that the performance of our diffuser is comparable to a commercially available Schroeder diffuser.
There exists a large gap between acoustic metasurfaces and their applications to real-world problems. Our findings may provide a roadmap to manipulate sound scattering using ultrathin acoustic metasurfaces and have far-reaching implications in architectural acoustics, noise control, and related areas.