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, among others. 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 ultra-thin and planar Schroeder diffusers are proposed based on the concept of acoustic metasurface. Both numerical and experimental results demonstrate satisfactory sound diffuse reflection produced from the metasurface-based Schroeder diffuser despite it being one order of magnitude thinner than the conventional one. The proposed design not only offer promising building blocks with great potential to profoundly impact architectural acoustics and related fields, but also constitutes a major step towards real-world applications of acoustic metasurfaces.
Highlights
In the 1970s, Schroeder published two seminal papers on sound scattering from maximum-length-sequence and quadratic-residue-sequence diffusers [1,2]
A simple recipe was proposed to design sound-phase grating diffusers with defined acoustic performance. These two papers opened a brand-new field of sound diffusers with applications in architectural acoustics [3,4,5], noise control [6,7,8], ultrasound imaging [9], and microparticle separation [10] and have inspired other disciplines such as energyharvesting photodiodes [11]
D’Antonio and Konnert [12] presented one of the most accessible review papers examining the theory behind Schroeder’s diffusers (SDs). They commercialized SDs and promoted them to be widely adopted in architectural acoustics, where the diffusers can be used to spread the reflections into all directions, reducing the strength of the undesired specular reflection and echo, as well as preserving the sound energy in space [3]
Summary
In the 1970s, Schroeder published two seminal papers on sound scattering from maximum-length-sequence and quadratic-residue-sequence diffusers [1,2]. In order to generate diffuse reflection for different incident acoustic waves, the phase shift at the surface of a SD must yield a specific profile such as a special number sequence [43].
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