Scattering effects emerging from time-varying metastructures: multi-mode generation and continuous spectrum radiation

Temporal metamaterials exploit the time dimension for achieving the time-equivalent scattering processes observed in space domain. Indeed, reflection and transmission, accompanied by frequency conversion, take place at a temporal interface, i.e., an instant of time at which the refractive index of the metamaterial changes suddenly. Recently, it has been proposed to achieve temporal metamaterials by exploiting the effective refractive index perceived by guiding modes by acting on the boundary conditions. In this contribution, we present our recent findings on boundary-induced temporal interfaces, discussing the scattering effects emerging from two parallel plate waveguides as time-varying metastructures and demonstrating that it is possible to achieve multi-mode generation and radiation of a continuous spatio-temporal spectrum, according to the design on the metastructure.