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 m) and nano-sized (20-30 nm) Ti particles based Fe O (80-100 nm) composites. The main objective of this study is to achieve good absorption with wide bandwidth corresponding to reflection loss (RL) dB for less coating thickness ( 1.5 mm). Waveguide measurements are carried out to obtain the effective complex dielectric permittivity ( ) and effective complex magnetic permeability ( ) values of Fe O -Ti based heterogeneous composites. The measured , , , and 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. Index Terms-Composite materials, fractals, frequency-selective surfaces (FSSs), microwave absorbing materials (MAMs).
Currently a wide range of materials are used for radar wave absorption. But, it is still a very challenging task to develop a thin radar wave absorber that operates for a wide range of frequencies. The main objective of this work was to achieve good absorption with wide bandwidth corresponds to reflection loss (RL) ≤ -10 dB for lower thickness (≤ 2.0 mm) by developing ferrite-graphene (FG) composites. A critical study has been carried out by varying the composition of FG to obtain wideband absorption with lower thickness. The effective complex dielectric permittivity (ε', ε'') and effective complex magnetic permeability (μ', μ'') of composites were measured using transmission/reflection waveguide method in the range of 8.2 to 12.4 GHz. These measured ε', ε'', μ', and μ'' values have been used for the design of single and double layer absorber. The increasing G content in FG composites resulted in a reduction of thickness and wide absorption bandwidth. Further, multilayer approach is adopted to enhance the radar wave absorption with broad bandwidth at a lower absorber layer thickness. The double layer absorber shows a strong RL of -55.28 dB at 10.2 GHz with broad bandwidth of 3.1 GHz in the frequency range of 8.6 to 11.7 GHz. The multi-layering approach facilitated to attain a lower absorber layer thickness of 1.7 mm. Findings provide an effective and feasible way to develop thin and broadband absorber which may be utilized for stealth applications.
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