Fractal Frequency-Selective Surface Embedded Thin Broadband Microwave Absorber Coatings Using Heterogeneous Composites

The development of thin microwave absorber coatings that operates for a wide range of frequencies is still a challenging task. This work presents a technique of blending a fractal frequency selective surface (FSS) with single- and double-layer coatings. These coatings are comprised of well-optimized micrometer-sized (80-90 μm) and nano-sized (20-30 nm) Ti particles based Fe3O4 (80-100 nm) composites. The main objective of this study is to achieve good absorption with wide bandwidth corresponding to reflection loss (RL) ≤ 10 dB for less coating thickness ( ≤ 1.5 mm). Waveguide measurements are carried out to obtain the effective complex dielectric permittivity ( ε r = ε r^´- jε r^´´) and effective complex magnetic permeability ( μ r = μ r^´- j μ r^´´) values of Fe3 O4-Ti based heterogeneous composites. The measured ε r^´, ε r^´´, μ r^´, and μ r^´´ values are used for the designing of double-layer composite absorbers, where the suitable composite selection, layer preferences, as well as thickness of layers are optimized using a genetic algorithm. The fractal geometry based FSSs have been designed using an iterated function system, which are embedded with single- and double-layer composite absorbers to examine their effect on absorption. A double-layer composite coating with a Sierpinski gasket fractal FSS shows a strong RL of 35.57 dB at 9.5 GHz with broad bandwidth of 4.2 GHz in the range from 8.2 to 12.4 GHz. The total coating thickness is only 1.4 mm. Findings provide an effective and feasible way to develop thin and broadband absorber coatings for various practical applications.