Design of a broadband electromagnetic absorbers based on TiO₂/Al₂O₃ceramic coatings with metamaterial surfaces

This paper presents a design method of wide-band radar absorber (RA) based on TiO₂/Al₂O₃ceramic coatings with metamaterial surfaces. The metamaterial surfaces are made up of periodic array of metallic patches consisting of circular and square aluminum film. The effects of design parameters on the reflectivity of RA were discussed, including the size, the period of metamaterial surfaces, and the thickness of ceramic coating. In addition, the effects of incidence angles for transverse electromagnetic (TE) and transverse magnetic (TM) polarization on the microwave absorption properties of RA were also investigated. Simulated results indicated that the microwave absorbing properties can be improved and adjusted by selecting the suitable unit dimensions of metamaterial surfaces, the RL is generally insensitive to incident angle from 0° to 30°. Finally, the design parameters of RA were optimized by Genetic Algorithms (GA) approach under normal incidence. Both the simulated results and measured results indicated that a bandwidth of reflection loss (RL) of single TiO₂/Al₂O₃ceramic coating below −10 dB is 0 GHz in the frequency range of X-band and Ku-band. By combination of metamaterial surfaces to ceramic coatings, a bandwidth with the reflectivity of RA below −10 dB can be obtained in the frequency range of 8.2–18 GHz for the thickness of the TiO₂/Al₂O₃coating of only 1.7 mm. The minimum value of reflection loss is −29 dB at about 10.6 GHz.