In the present work, synthesized U-type barium hexagonal (Ba4Co1.5Zn0.5Fe36O60 or BaU) ferrite powder is further transformed into BaU/glass fiber-epoxy structural composites by hand lay-up process and compression moulding techniques using different volume percentages (11.4, 17, and 26.4) within reinforced polymer matrix. Phase formation, surface morphology, and magnetic properties by XRD, FESEM, and VSM techniques, respectively. Subsequently, the electromagnetic and absorbing properties of the designed structures were measured for typical incident EM waves in the frequency range of the C-band. The radar absorbing performance of the designed RAS composites was observed as -16.8 dB in the whole band, with maximum absorption (RL <= -10 dB) of adequate thickness at 2.2 mm. Additionally, the effects of the BaU particles on the mechanical properties of the designed polymeric composites were measured through ASTM standard data. The proposed RAS composites are the most demanding absorbers from a military and commercial point of view.

In the current study, U-type barium hexaferrite (BHF) poly-crystalline powder with chemical formula Ba4Co2-xZnxFe36O60 (0.5 <= x <= 1.5 in step of 0.5) were successfully synthesized by solid state reaction route at the sintering temperature of 1400 degrees C in air medium. The effect of Zn+2 substitutions on the crystalline structural and magnetic properties of BHF powders were examined through nondestructive X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM) respectively. Upon increasing Zn+2 content the lattice parameters a and c decreases which is leading to the X-ray density up to a small degree, due to a smaller ionic size of Zn+2 as compared to Co+2 ions and saturation magnetization (M-s) from 56.08 emu/g for the zinc substituted sample down to 54.79 emu/g was observed. The transmission electron microscope (TEM) depicted that the particle size reached a minimum at x = 0.5 and then grown with x = 1.5 zinc content, getting a value of 103.06 nm with hexagonal phase and finer grains having the size range of similar to 0.51-1.0 mu m thick and 5 mu m long which is confirmed by field emission scanning electron microscopy (FESEM). A series of BHF-epoxy composites has been further transformed into toroidal shaped composites with fix volume percentage (54.3 vol%) of BHF powder in epoxy matrix. Electromagnetic properties; complex permittivity (epsilon(r) = epsilon' - j epsilon '') and complex permeability (mu(r) = mu' - j mu '') of the prepared composites were computed through coaxial measurement techniques by using an Agilent E8364B vector network analyzer. Minimum return loss (RLmin) was observed as -32.98 dB (maximum absorption " 99.92) for matching frequency 10.3 GHz of the absorber with thickness of 3.1 mm and the bandwidth achieved was 7.38 GHz. Absorption values for prepared composites have potential use as excellent microwave absorbers over the frequency band C-band, X-band and Ku-band. (C) 2021 Elsevier B.V. All rights reserved.

Micron size U-type barium hexaferrite powder have been synthesized by solid state reaction process. Powder X-ray diffractometer technique has been used to confirm the phase of hexagonal through the calculate lattice parameters. Field emission scanning electron microscope was used to morphology of synthesized powder and prepared composites. Complex permittivity, complex permeability and absorbing properties have been studied for all polymeric composites by using the Agilent vector network analyzer in the frequency range of 2-18 GHz. The minimum RL was observed as -32.38dB for the absorber with thickness of 3.6mm.

Electromagnetic absorbers based on carbonaceous materials, i.e., carbon black, polyaniline, polypyrrole, carbon fiber, etc., are prominently employed to attenuate incident electromagnetic waves. In the current work, exfoliated graphite (EG) was synthesized with swollen expanded volume from graphite flake by using a simple and inexpensive method. After synthesis, a series (8.9, 22.9, 33.3, 41.4 and 44.7 volume percentage) of EG–epoxy composites were prepared using a wet mixing method. EG and the prepared composites were characterized by x-ray diffraction analysis, field-emission scanning electron microscopy, and energy-dispersive x-ray analysis. An Agilent vector network analyzer (model PNA E8364B) was employed to compute the complex permittivity (εr = ε′ − jε″) of the prepared composites in the frequency range of 2 GHz to 18 GHz. The dielectric loss of the prepared EG–epoxy composites was quantified in terms of the loss tangent (tanδe = ε″/ε′). Their radar absorption properties were evaluated in terms of the return loss (RL), which in turn was calculated for varying thicknesses of the prepared composites using the computed complex permittivity data. The measured minimum RL was −26.4 dB for the absorber with thickness of 4.0 mm, and the bandwidth achieved was 5.2 GHz for RL ≤ − 10 dB in the effective frequency region of 8 GHz to 14 GHz. The matching frequency shifted towards downwards with increasing EG content in the epoxy thermosetting matrix according to both the calculated and measured data. Consequently, the prepared composites exhibited good complex permittivity, dielectric tangent loss, and microwave absorption and could be utilized in the design of electromagnetic interference shielding and absorbers for stealth applications.

•U-type barium hexaferrite (Ba4Co2Fe36O60) powder was synthesized.•Four different ferrite-epoxy composites were fabricated.•Complex permittivity and permeability of fabricated composites were computed.•Microwave absorption properties were calculated in terms of return loss (RL).•Minimum return loss (RL) ≤ −10 dB was achieved for all the fabricated composites.