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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).

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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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In this work, Fe2Mo intermetallic powder, produced by H2 gas reduction of Fe2MoO4 was characterized by techniques like x-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM studies confirmed the presence of nano- and microcrystalline grains of Fe2Mo. The above powders when compressed uniaxially showed a logarithmic relation with “relative density”, δr, of the compacts. The multiple compaction mechanisms were analyzed by Kawakita's and Balshin's models. Vickers hardness number, VHN, was found to increase linearly with δr of the compacts. The hardness of Fe2Mo intermetallic when δr = 1 was estimated as 343 VHN. Using Tabor's analysis, the yield strength of Fe2Mo was found to be about 1100 MPa. This value was further confirmed from the details of relative broadening (112) Bragg peak of Fe2Mo obtained from XRD analyses of Fe2Mo at different compaction pressures.

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