3D Printed quadratic residue metadiffuser - Design and measurements of an optimized deep-subwavelength sound diffuser

It has been two years since the first publication of the novel concept of metadiffusers. Heavily based on critical coupling theory introduced in the case of perfect absorption in deep-subwavelength metamaterials, metadiffusers are presented in a similar fashion, i.e. slotted panels with thin slits, each one backed with a set of critically coupled Helmholtz resonators (HRs). Instead of focusing on absorptive and transmitting properties, metadiffusers emphasize on perfect or pseudo-perfect reflection of sound. Here a particular interest is given to the scattering patterns obtained by the customization of the metamaterial's geometry. The deep-subwavelength nature of the structure leads to dimensions 20 to 46 times smaller than the design wavelength, i.e. about 1/20th to 1/10th of the thickness of traditional designs. This presentation aims at introducing the physical aspects of sound propagation in and out of the metadiffuser, emphasizing on deep-subwavelength critical coupling, on the consequent strong dispersion relations and on the custom scattered fields. This theoretical overview will then be paired with numerical and experimental data of a 3D-printed quadratic residue metadiffuser (QRM). Finally, potential applications of such structures will be discussed in critical industry environments.