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Abstract
An acoustic metadiffuser is a subwavelength locally resonant surface relying on slow sound propagation. Its design consists of rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Due to the slow sound properties, the effective thickness of the panel can therefore be dramatically reduced when compared to traditional diffusers made of quarter-wavelength resonators. The aim of this work is to experimentally validate the concept of metadiffusers from the scattering measurements of a specific metadiffuser design, i.e., a quadratic residue metadiffuser. The experimental results reported herein are in close agreement with analytical and numerical predictions, therefore showing the potential of metadiffusers for controlling sound diffusion at very low frequencies.
Highlights
An acoustic metadiffuser is a subwavelength locally resonant surface relying on slow sound propagation and consisting of rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators (HRs)
The spatially-dependent reflectivity of a sound diffuser is generally tailored following numerical sequences with a uniform spatial Fourier transform of their reflection coefficient such as the Quadratic Residue (QR), Maximum Length (MLS), Primary Root (PR) or Index sequences2,3. These structures, called Schroeder diffusers, are designed using rigidly-backed slotted panels where each well acts as a quarter-wavelength resonator (QWR)
These phasegrating diffusers become thick and heavy structures when designed to manage low-frequency waves, e.g., the typical thickness of a quadratic residue diffuser (QRD) is quarter of the wavelength corresponding to the low cut-off frequency
Summary
An acoustic metadiffuser is a subwavelength locally resonant surface relying on slow sound propagation and consisting of rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators (HRs). We 3D printed a one-dimensional QR metadiffuser (QRM); meaning it only scatters sound efficiently in one plane; and experimentally characterized its diffusion properties in an anechoic chamber following the standard ISO 17497-2:201218.
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