  A radial-dependent dispersive finite-difference time-domain (FDTD) method is
proposed to simulate electromagnetic cloaking devices. The Drude dispersion
model is applied to model the electromagnetic characteristics of the cloaking
medium. Both lossless and lossy cloaking materials are examined and their
operating bandwidth is also investigated. It is demonstrated that the perfect
"invisibility" from electromagnetic cloaks is only available for lossless
metamaterials and within an extremely narrow frequency band.
