M2 : Fundamental limits of passive cloaking on a frequency bandwidth : numerical investigation.

While cloaking at a single frequency has been established (even experimentally [12]) for passive cloaks (i.e., cloaks without active energy sources), it is much less certain that one can cloak over an interval of frequencies as metamaterial are very dispersive media (see [3, 14] and [4]), i.e., highly frequency dependent. Yet, passive cloaks have only been explored for single frequency waves which is unrealistic. Indeed by nature, a time-dependent electromagnetic wave has a whole characteristic frequency bandwidth. Hence, one can achieve cloaking at one frequency, but at the same time increases the signature of the object at another frequency making the cloak device useless for broadband signals.
Is it possible to construct a cloak made of a passive electromagnetic material that cloaks an object over
a broad frequency band? If not, what are the fundamental limitations to cloaking and performance bounds
on cloaking devices over a finite frequency range? Finally in that case, can one synthesize broadband cloaks which achieve the optimal bounds which significantly decrease the signature of an object on a given frequency band and thus makes the object hardly detectable in this frequency range?

Stage_Cassier_Demesy