Influence of depth variation on ultra-thin diffusers

In recent years, there has been a lot of progress in state-of-the-art technology about the design of acoustic metamaterials for controlling sound fields. Among the most recent developments are ultra-thin diffusers that scatter sound similarly to the classic Schroeder quadratic residue diffusers. A design proposed by Zhu in 2017 generates subwavelength diffusers with constant depth on the order of λ/20. Scattering is achieved by changing the window size of different resonators. This characteristic is advantageous for low frequencies or spaces of reduced dimensions. In this paper the influence of depth variation on these ultra-thin diffusers is analyzed. Simulation results and experimental measurements of ultra-thin models using a depth different from that described by Zhu are shown to compare with quadratic residue diffusers built to scale in 3D printing.