Sharif Digital Repository

Readily oxidization of magnetic particles is a common drawback of these type of materials which reduce their electromagnetic wave dissipation performance. In this study, the magnetic core-double shells structured (Ni/SiO2/Polyaniline) composite has been developed for protection of the core from oxidation and in consequent improvement the complex permittivity. Solvothermal and in-situ polymerization methods were utilized for decorating Ni micro-particles with SiO2 and conductive polyaniline polymer respectively. All physico-chemical, magnetic and electromagnetic features were evaluated via XRD, FTIR, XPS, FESEM, VSM and VNA analysis. The double shells composite possesses significant... 

In this study, effectiveness of non-ionic block copolymers such as Lugalvan BNO12 and Triton X series (Triton X100 & Triton X405) has been reported for graphene dispersion in aqueous solutions. Stability of the aqueous graphene dispersions is investigated using UV–visible spectroscopy, Rheological, and Conductivity studies. Adsorption isotherms are constructed to determine the amount of polymers adsorbed on the surface of graphene by the spectroscopic analysis. Lugalvan BNO12 has been found to be adsorbed in higher amounts on the graphene surface compared to the Triton X series polymers. Thermogravimetric analysis (TGA) and Fourier Transform Infrared (FTIR) Spectroscopy investigations... 

Perfect metamaterial absorbers (PMAs) are crucial for sensing, energy harvesting, cloaking, and solar cell, as these can perfectly absorb electromagnetic waves in the broad range of electromagnetic spectra. Due to these remarkable applications, PMAs have extensively attracted the attention of numerous researchers. However, to date, narrow- and wide-band absorbers have been investigated, recently wideband absorption is the primary concern of electromagnetic communities. In this paper, absorption features of the metasurface-based absorber are analyzed. The PMA is made of three layers–a top metasurface fabricated over silicon dioxide (SiO2) with a backside coated with a thin layer of silver... 

In this study, a novel double-layer microwave absorber was designed based on the MWCNTs/La0.6Sr0.4Mn0.5Fe0.5O4 (C/LSMFO) and PEDOT-coated (P@[C/LSMFO]) nanocomposites. Co-precipitation and in-situ polymerization methods were utilized to synthesize the C/LSMFO and P@[C/LSMFO] nanocomposites, respectively. XRD, FESEM, VSM, and VNA analysis were used to determine the structural, morphological, magnetic, and electromagnetic properties of the nanocomposites. Single-layer absorbers with thicknesses of 1, 1.5, and 2 mm were fabricated, and electromagnetic parameters were evaluated via VNA in the X-band frequency. Moreover, the microwave absorbing features of the double-layer absorber with various... 

Single phase Ca-substituted W-type hexaferrites Sr1-xCaxZn2Fe16O27(x = 0.00(0.25)1.00) have successfully been synthesized by using sol–gel self-combustion at 1300°C. These hexaferrites are investigated by x-ray difrractometry (XRD), scanning electron microscopy, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and vector network analysis. XRD analysis confirms the formation of a single W-type hexaferrites phase. The DC electrical resistivity increases with incrementing Ca contents. The morphology of all the hexaferrites shows hexagonal platelet-like structure. The prepared ferrites depict soft magnetic nature with high saturation... 

Co–Zr doped Ni ferrite substituted polyaniline (PANI) nanocomposites were prepared using polymerization reaction method. NiFeCo0.5Zr0.5O4 with 12.5%, 25%, 37.5% and 50% PANI (A1, A2, A3 and A4) were used to obtain better photocatalytic efficiency. XRD, UV/VIS, BET, and FESEM were employed to characterize the PANI/ferrite nanocomposites. The effect of reaction time and nanoparticle concentrations on the photocatalytic degradation were thoroughly evaluated. XRD analysis confirmed the phase of NiFeCo0·5Zr0·5O4ferrite, while FESEM analysis was performed to investigate the surface morphology of the nanocomposites. The crystallinity was increased with the Co–Zr doped Ni ferrite contents in the... 

Using the first-principles procedure of density-functional-theory within tight-binding approximation and nonequilibrium Green's function formalism, this paper reports on the impact of vacancy defects on the structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet. After the introduction of vacancy defects in graphene atomic sheet passivated with hydrogen atoms, apart from increase in band gap, a suppression is noted in the intensity of transmission channels and density of states arising from the long array deformations of the graphene sheet and a corresponding shift of the Fermi level. This in turn decreases the conductance of the defected graphene atomic... 

Multiband absorption is the interest of the microwave communities due to several applications in sensing, filtering, and stealth. Usually, the stacking of metal and dielectric multilayered structures form a multiband absorber which makes the device bulky and costly. In this paper, we investigate a multiband absorber based on a single-layered fractal metasurface for the 5G applications. The unit cell of the fractal metasurface is comprised of six ring-shaped symmetric split-ring resonators (SRRs) connected back-to-back with each other. The absorptivity is investigated in the 5G microwave regime (22–36 GHz) for various obliquities at different substrate thicknesses. Simulation results show... 

Indium substituted Cu[sbnd]Ni nanoferrites with nominal compositions Cu 0.5 Ni 0.5 In x Fe 2-x O 4 (x = 0.00–0.32)were successfully synthesized by sol-gel auto ignition method. X-ray diffraction patterns illustrated the single phase spinel structure for x ≤ 0.24. The lattice parameter ‘a’ increased from 8.3349 to 8.3723 Å and then it decreased for x = 0.32. X-ray density increased from 5.43 to 5.79 g/cm 3 . The average crystallite sizes lie in the range 33.21–17.78 nm. The cell volume was increased from 579.03 to 586.86 Å 3 with the substitution of indium ions into the spinel lattice of copper nickel ferrites. The compositional dependence of tetrahedral and octahedral radii was explained on... 

In this work, Sr-substituted samples of single-phase spinel monoferrites with chemical formula Ba1-xSrxFe2O4 (x = 0.00, 0.33, 0.67, 1.00) were synthesized using sol-gel auto-combustion method. In order to confirm the single-phase formation of these samples, a sample (x = 0.00) was chosen for heat treatment at different temperatures (100, 300, 400, 600 and 700°C) for 4 h. The heat treated sample was then investigated by X-ray diffraction (XRD) analysis and results showed that a single-phase sample can be successfully synthesized at a temperature of 600°C, which is much lower than that reported in earlier literature for synthesis of same structured samples. All the synthesized samples were... 

Herein, two distinct nanocomposites of CaTiO3 micro-cubes and polygonal SrFe12O19, both decorated with NiO nanoparticles, were successfully synthesized using hydrothermal method. The physico-chemical features of as-prepared samples were evaluated via XRD, FTIR, UV–vis, BET, XPS, FESEM and EDS analysis. Microwave attenuation features of as-prepared single layer absorbers were determined by VNA analysis in 2–18 GHz. Simulation confirmation was checked by preparing a bi-layer samples and evaluating it using VNA analysis after finding the appropriate thickness of each layer. The reflection loss from each single layer samples containing 20 wt% of each CaTiO3/NiO and SrFe12O19/NiO nanocomposites... 

In this study, ternary MWCNTs/CoFe2O4/FeCo nanocomposite coated with conductive PEDOT-polyaniline (PA@MW/F/C) co-polymers were synthesized by microwave-assisted sol-gel followed in-situ polymerization methods. The phases, crystal structures, morphologies, magnetic and electromagnetic features of the as-prepared samples were identified via XRD, SEM, XPS, VSM, and VNA respectively. Absorption characteristics were investigated in the frequency (12–18 GHz) Ku band. XRD, VSM and SEM analysis confirmed the partial reduction process of CoFe2O4 and successfully decorated magneto-dielectric particles with co-polymers. By measuring electromagnetic features of the samples, it was found that coating... 

Copper (Cu) substituted Co–]Ce nanoferrites with nominal composition of Co 1-x Cu x Ce 0.05 Fe 1.95 O 4 (x = 0.00, 0.25, 0.50, 0.75, 1.00) were prepared by sol-gel route. The sintering of the Cu doped Co–]Ce nanoferrites was done at 700 °C to investigate the desired properties of the Cu doped Co–]Ce nanoferrites. The combination of transition metal (Cu) and rare earth (Ce) were employed to tailor the characteristics of the spinel ferrites. The constant ratio of rare earth and systematic doping of Cu in Co ferrite was incorporated to see the effects of these ions in spinel ferrite. FTIR, FESEM, XRD and VSM were used to study the vibrational bands, phase, morphology, structure and magnetic... 

Co-Ce doped Ni nanocrystalline ferrites having composition Ni0.8Ce0.2CoxFe2-xO4 with x = 0.00, 0.25, 0.50, 0.75, 1.00 were fabricated by sol gel auto combustion method. Synthesized samples were investigated by thermal gravimetric and differential thermal analysis (TGA-DTA), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis (EDX) and vibrating sample magnetometer (VSM) to study the phase, vibrational modes, structure, surface analysis and magnetic properties respectively. Structural parameters (lattice parameters, cell volume, crystallite size and micro strains) were also calculated from XRD recorded data.... 

There has been a growing demand for materials with superior absorption capabilities, such as strong absorbing capacity, thin thickness, and light weight, to solve challenges related to EM radiation pollution. While the majority of the research is focused on optimizing material compositions, component microstructure and absorber structure are also critical factors for improving microwave absorption performance. In this research, we show how the microstructure of components and absorber design may increase dissipation features. Solvothermal and hydrothermal methods were utilized for synthesizing mesoporous CuS micro-particles with a 3D hierarchical structure as a dielectric component and... 

Gadolinium (Gd) and cobalt (Co) substituted Sr–Ba–Cu-based Y-type hexaferrites were synthesized with the help of the sol–gel auto-combustion route. XRD (X-ray diffraction) analysis was done to ratify the phase formation of hexaferrites. The impact of Gd3+ substitutions was measured on all the lattice parameters. Lattice constants “a” and “c” were found between 5.879–5.891 Å and 43.185–43.620 Å, respectively. It was observed from the XRD analysis that with an increase in Gd–Co contents, the enhancement in the average crystallite size is noted. The thermal decomposition process was studied using TGA (thermogravimetric analysis), revealing that the precursor may give the ending product when... 

The mixed nano-ferrites materials Cu0.6Zn0.4HoxFe2−xO4 (0.00 ≤ x ≤ 0.12) were prepared via the sol–gel auto combustion technique. The TGA curve established the annealing temperature (500 °C) for phase formation. The single exothermic peak on the DSC plot occurred at 341 °C temperature. XRD patterns of these nano ferrites verified single phase formation of the FCC cubic structure. The lattice constant a was increased from 8.4244 to 8.4419 Å and then its value decreased to 8.4319 Å. Crystallite size was found in the range of 7 to 16 nm. The surface morphology of the samples was observed from the scanning electron microscope (SEM) images. The grain size was found within the range of 90 nm to... 

The mixed nano-ferrites materials Cu0.6Zn0.4HoxFe2−xO4 (0.00 ≤ x ≤ 0.12) were prepared via the sol–gel auto combustion technique. The TGA curve established the annealing temperature (500 °C) for phase formation. The single exothermic peak on the DSC plot occurred at 341 °C temperature. XRD patterns of these nano ferrites verified single phase formation of the FCC cubic structure. The lattice constant a was increased from 8.4244 to 8.4419 Å and then its value decreased to 8.4319 Å. Crystallite size was found in the range of 7 to 16 nm. The surface morphology of the samples was observed from the scanning electron microscope (SEM) images. The grain size was found within the range of 90 nm to... 

Hydrothermal and in-situ polymerization methods were used to successfully fabricate a pompon flower-like CoGd0.5Fe1.5O4 (CG) as a magnetic component and a cauliflower-like poly(indole-co-Py) (PP) co-polymer as a dielectric component for microwave absorption. The physico-chemical properties of CG/PP samples were determined via XPS, XRD, FTIR, BET, UV–vis, EDS, and FESEM analysis. VNA and VSM were used to evaluate the dielectric and electromagnetic properties of the CG and PP samples. The results of the absorption capability tests revealed that bi-layer samples outperformed single layer samples in terms of microwave dissipation capability. The thickness and arrangement of each layer in bilayer... 

The present study is focused on the investigation of the absorption properties of the bi-layer absorber with different thickness and orientation approaches. Improvement in absorption exclusively depends on the various parameters as interfacial polarization, multiple reflections among layers, conduction loss, phase cancellations, and shape anisotropy, etc. By considering these parameters. Calcium titanate micro-cubes CaTiO3 (CTO) and polypyrrole nanotubes (PPy) nanocomposites were prepared and microwave absorption from single layer coaxial absorbers having M1 = CaTiO3+15 wt% polymer and M2 = CaTiO3+30 wt% polymer were determined. Different layer orientations and thicknesses of the bi-layer...