Fractional-order acoustic diffraction rings: A nonlocal computational framework for scattering surface-launched waves

Abstract

Several recent studies showed that nonlocal metasurfaces have great potential for guiding and exploiting nonlocal acoustic and electromagnetic phenomena. In this work, we provide a generalized description of the potentialities of acoustic nonlocal metasurfaces using a fractional-order hybrid-waves framework (i.e., a mixture of surface phonon polaritons and quasi-cylindrical waves). We provide a general investigation into the emergence of nonlocal resonant dynamics (resulting, for example, from multiple scattering, wave-field attenuation, and local enhancement) and, in particular, the occurrence of Wood-like anomalies due to bounded modes within the acoustic metasurface. The occurrence and transition between these phenomena are investigated by computational results obtained via a fractional-order hybrid-waves framework. The intrinsic capabilities of the proposed mathematical framework offer a novel route for guiding and exploiting a plethora of hybrid-wave transport effects with important implications from material characterization (e.g., Raman scattering) to bio-oriented applications.