Synchronization driven acoustic nonreciprocity

This contribution investigates the scattering properties of aeroacoustic limit cycles and their reciprocity-breaking interactions. Specifically, a mean tangential flow grazing an aperture is employed to generate a self-sustained cavity mode (a whistle), providing a framework for analyzing the acoustic scattering behavior of a self-excited, sub-wavelength structure, referred to as a meta-atom. The nonlinear interactions within a system of coupled meta-atoms are then harnessed to control the wave propagation in an acoustic waveguide, demonstrating phenomena such as synchronization-driven superradiance, unidirectional transmission and unidirectional transparency. Furthermore, using the mean flow as a control signal enables the management of the wave propagation path across multiple waveguides connected to the meta-atom assembly. Additionally, the experimentally observed phenomena have been successfully described by a minimal model of a nonlinear saturable gain oscillator. The model's autonomous and non-autonomous dynamics, as well as its synchronization properties, are shown to align with experimental measurements.