Equivalent circuit model and microwave reflection loss mechanism of double-layer spiral-ring metasurface embedded composite microwave absorber

High-performance absorbing material can play an important role in electromagnetic compatibility, electromagnetic radiation protection, and anti-detection of special equipment. Combining traditional absorbing material with metamaterial is an important direction for developing absorbing material. The composite absorbing body based on the development of metamaterial has advantages of thin thickness, light weight, strong absorption, and adjustable absorption band, but the super material absorption body composed of single-sized metal pattern elements possesses generally strong absorption only for electromagnetic waves at a certain frequency. It is difficult to meet the requirement for wide frequency absorption in practical applications. In order to broaden the absorption bandwidth of metamatial, metal spiral-ring metasurface coated short carbon fiber absorber with enhanced microwave absorbing performance is proposed. The absorber is a two-dimensional structure formed by periodically arranging a large number of individual absorber units in the horizontal and vertical direction. In the HFSS simulation software, a " master-slave boundary condition” consisting of " master boundary” and " slave boundary” is provided. Under this boundary condition, the electric field between adjacent boundaries has a phase difference, which can be used to simulate an infinite array. The research results show that the obvious enhancement of both the absorption peak and bandwidth can be observed by embedding the double-layer spiral-ring metasurfaces. The increase of initial length of spiral-rings and thickness of absorber are beneficial to further enhancing the microwave absorption. The reflection loss from 9.2 GHz to 18.0 GHz are under –10 dB (the bandwidth reaches 8.8 GHz), and the peak of S11 is –14.4 dB. Besides, we find that the effective electromagnetic parameters and impedance of spiral-ring metasurface embedded microwave absorber present obvious resonant phenomenon at multi-frequencies by calculating S parameters. Furthermore, an equivalent circuit model regarding double-layer spiral-ring embedded absorber is established to reveal the attenuation mechanism of microwave energy. The resonant frequencies derived from this model are well accord with the simulated results. Thereby, the multi-electromagnetic resonant frequencies make the composite microwave absorber combined with double-layer metal spiral-ring and carbon fiber have microwave reflection loss in a wide bandwidth.