Symmetric Absorbers Realized as Gratings of PEC Cylinders Covered by Ordinary Dielectrics

Nearly all known electrically thin perfect absorbers are asymmetric with respect to their two sides and show perfect (rather, nearly perfect) absorption only from one side of the absorbing layer. Moreover, the vast majority of the designs contain a ground plane, which makes the transmission coefficient zero at all relevant frequencies. Here, we introduce a simple symmetric configuration of a single infinite grating of perfectly conducting rods coated by ordinary dielectrics as a symmetric single-layer perfect absorber not containing any impenetrable layers. With the goal to examine its capacity to absorb electromagnetic radiation, we replace each cylinder by a pair of dipole lines and derive the conditions for the perfect absorption (zero reflection and zero transmission) in terms of their dipole moments. It is a general approach that is not limited to circular cylinders or homogeneous textures; in this way, the generic concept of carrying over properties from simpler to more complicated structures, is realized. A metric of fulfilling the aforementioned two requirements for perfect absorption is defined and evaluated for a number of different cases. A realistic example design demonstrating 96%-97% absorption is presented. The performance can be increased further to reach 98% absorption in case of permitting arbitrary permittivities.