Non-reciprocal wave propagation in discretely modulated spatiotemporal plates

We investigate non-reciprocal wave propagation in spatiotemporal phononic plates. Specifically, the first aim of this manuscript is to propose a general formulation of the Plane Wave Expansion Method (PWEM) that, in contrast with previous works, is applicable to any class of 2D spatiotemporal unit cells whose properties can be expanded in traveling plane waves. The second aim is to exploit this analysis tool in order to study a class of phononic materials capable of violating mirror symmetry in reciprocal space, therefore breaking reciprocity principle along different propagation directions in physical space. This is obtained by considering the plate elastic properties to be discretely modulated in space and continuously in time. Theoretical dispersion profiles are validated and compared with numerical simulations.