Simplified formulation and realization for ultrathin near perfect absorbers with rectangular microstrip elements using cavity and transmission line models

摘要

Ultra-thin absorbers are studied theoretically in detail to provide an in-depth model for their absorption behaviour. In this work, the absorption resonance of the ultrathin rectangular patch absorber is analysed using both cavity and transmission line models. A single rectangular patch structure with grounded dielectric substrate has been used as an absorber to explain the analytical model proposed. The cavity model analysis shows that the ultrathin structure act as a lossy resonator which exhibits absorption due to the dominance of the non-transverse electric field component launched on the patch unit cell structure at the absorption resonance. The cavity model analysis of a single patch element including fringing effects is demonstrated to closely estimate the absorption resonance. A novel transmission line model is also proposed in this work based on the cavity model analysis and simulations. The transmission line model (TML) simply represents the rectangular patch absorber unit cell by two identical slots separated by a transmission line. The two absorbing slots are then proven to be represented by two identical parallel equivalent (RC) circuit connected in series with a transformer (L). The dimensions of the unit-cell are presented as a function of the LC circuit parameters using simple equations. The variation effect of the absorber parameters (patch length, patch width & substrate thickness) are investigated based on the proposed equivalent model. The deviation between the simulated, analytical and equivalent circuit model calculations is plotted for the absorber parameters' variation. Also, the mean error and the standard deviation values for the proposed analysis are shown to be below 0.1 and 0.02 respectively.