Ultrathin Broadband Absorber Using Frequency-Selective Surface and Frequency-Dispersive Magnetic Materials

The bandwidth of frequency-selective surface (FSS)-based absorber decreases when high permittivity material is used to reduce the thickness of the absorber. A solution of this thickness-bandwidth dilemma was presented by using resistive FSS layer and frequency-dispersive magnetic material (FDMM) in substrate. The FDMM was designed for a certain profile of complex permeability, and the FDMM substrate has both high permeability and permittivity for thickness reduction and near frequency-nondispersive input susceptance for bandwidth expanding at low frequencies. A 2.3 mm thick FSS-based FDMM absorber was designed and fabricated, which achieved a broad absorption band of 4-15 GHz (3.75:1) with -10 dB reflectivity. In terms of the same bandwidth ratio, the thickness of FSS-based FDMM absorber is only 0.031λ
_L
against the thickness of 0.114λ
_L
of conventional FSS-based absorber.