Double-Negative Temporal Acoustic Metamaterials

Metamaterials with temporal modulation of constitutive parameters have recently emerged to the scientific spotlight, featuring the novel concept of temporal boundaries. These boundaries, which are artificial by spatial means, cause in-domain wave reflection and transmission at a temporal frequency different from that of the source, in contrast to the case of spatial boundaries or interfaces. Here we study a new form of temporal modulation, which drives the system from a dispersionless to a dispersive state in both constitutive parameters, supporting the so-called Drude model. We demonstrate that the resulting temporal boundary generates waves simultaneously in two different dynamical regimes, double-negative and double-positive, for a single frequency source, which is an otherwise unachievable response.