@Article{CiCP-17-822, author = {Zhiguo Yang and Li-Lian Wang}, title = {Accurate Simulation of Circular and Elliptic Cylindrical Invisibility Cloaks}, journal = {Communications in Computational Physics}, year = {2018}, volume = {17}, number = {3}, pages = {822--849}, abstract = {
The coordinate transformation offers a remarkable way to design cloaks that
can steer electromagnetic fields so as to prevent waves from penetrating into the cloaked
region (denoted by $Ω_0$, where the objects inside are invisible to observers outside).
The ideal circular and elliptic cylindrical cloaked regions are blown up from a point
and a line segment, respectively, so the transformed material parameters and the corresponding
coefficients of the resulted equations are highly singular at the cloaking
boundary $∂Ω_0$. The electric field or magnetic field is not continuous across $∂Ω_0$. The
imposition of appropriate cloaking boundary conditions (CBCs) to achieve perfect concealment
is a crucial but challenging issue.
Based upon the principle that a well-behaved electromagnetic field in the original
space must be well-behaved in the transformed space as well, we obtain CBCs that
intrinsically relate to the essential "pole" conditions of a singular transformation. We
also find that for the elliptic cylindrical cloak, the CBCs should be imposed differently
for the cosine-elliptic and sine-elliptic components of the decomposed fields. With
these at our disposal, we can rigorously show that the governing equation in $Ω_0$ can
be decoupled from the exterior region $Ω^c_0$, and the total fields in the cloaked region
vanish under mild conditions. We emphasize that our proposal of CBCs is different
from any existing ones.
Using the exact circular (resp., elliptic) Dirichlet-to-Neumann (DtN) non-reflecting
boundary conditions to reduce the unbounded domain $Ω^c_0$ to a bounded domain, we
introduce an accurate and efficient Fourier-Legendre spectral-element method (FLSEM)
(resp., Mathieu-Legendre spectral-element method (MLSEM)) to simulate the circular
cylindrical cloak (resp., elliptic cylindrical cloak). We provide ample numerical results
to demonstrate that the perfect concealment of waves can be achieved for the ideal
circular/elliptic cylindrical cloaks under our proposed CBCs and accurate numerical
solvers.