Spatio-temporal modulated doppler cloak restores invisibility of moving cloaked objects

In this contribution, we report our results on the possibility of restoring the invisibility of cloaked objects in relativistic motion by using a spatio-temporal (ST-) modulated cover wrapped around or just in front of the object. It consists of an artificial dielectric whose refractive-index is modulated as a periodic function in both space and time, leading to a periodic profile of the refractive index that moves with a certain velocity. The periodicity of the spatial modulation and the modulation frequency are properly chosen in order to frequency modulate the propagating signal in the cover. We show that by properly choosing the modulation scheme and frequency of the ST-modulated cover, it is possible achieving a full compensation the Doppler frequency shift, restoring the operation frequency of the cloak and, thus, the invisibility of the object.