An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series RLC resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.