Investigation of metamaterial coated conducting cylinders for achieving transparency and maximizing radar cross section
Recently, reducing the radar cross sections (RCS) of various structures to achieve transparency and obtaining resonant structures aimed at increasing the electromagnetic intensities, stored or radiated power levels have been investigated. The transparency and resonance (RCS maximization) conditions investigated in are mainly attributed to pairing of "conjugate" materials: materials which have opposite signs of constitutive parameters [e.g., double-positive (DPS) and double- negative (DNG) or epsilon-negative (ENG) and mu-negative (MNG)]. In the present work, we extend the transparency and resonance conditions for cylindrical structures when the core cylinder is particularly perfect electric conductor (PEC). The appropriate constitutive parameters of such metamaterials are investigated for both TE and TM polarizations. For TE polarization it is found out that, the metamaterial coating permittivity has to be in the 0 < epsivc < epsiv0 interval to achieve transparency, and in the -epsiv0 < epsivc < 0 interval to achieve RCS maximization. As in the case of "conjugate" pairing, transparency and resonance are found to be heavily dependent on the ratio of core-coating radii, instead of the total size of the cylindrical structure. However, unlike the "conjugate" pairing cases, replacing epsiv by mu (and vice versa) does not lead to the same conclusions for TM polarization unless the PEC cylinder is replaced by a perfect magnetic conductor (PMC) cylinder. Yet, RCS maximization can also be achieved in the TM polarization case when coating permeability muc < 0, whereas transparency requires large \muc\ for this polarization. Numerical results, which demonstrate the transparency and RCS maximization phenomena, are given in the form of normalized monostatic and bistatic echo widths.