Coupled Mode Theory for Scattering from Acoustic Waveguides with Spatiotemporally Modulated Boundaries

Abstract

Recent research in optical, electromagnetic, and acoustical metamaterials has shown that spatiotemporal modulation of bulk properties and of interfaces between material domains can be used for unprecedented control of wave propagation and scattering. Spatiotemporal modulation of bulk properties has been used to enable nonreciprocal wave propagation in unbounded systems and to couple modes at different frequencies in bounded systems through frequency and wavenumber conversion. This work employs a Fourier series expansion-based coupled mode approach to investigate coupling between guided wave modes in an acoustic waveguide with different frequency-wavenumber pairs using spatiotemporal modulation of a single boundary. Results demonstrate the ability to couple incident plane waves to non-radiating (trapped) modes and to generate radiation from incident evanescent fields.