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The electromagnetic (EM) and microwave absorption properties of (Co2+–Si4+) substituted barium hexaferrite compositions BaCox2+Fey+2Six+y4+Fe12−2x−2y+3O19 (x=0.9 and y=0.0, 0.05, and 0.2) and its polymer composites prepared from hexaferrite, polyaniline, and carbon powders dispersed in polyurethane matrix have been investigated at the microwave frequency range of the X band (8.2–12.4GHz). The hexaferrite compositions were synthesized by solid-state reaction technique, whereas polyaniline, by chemical route. The permeabilities of a ferrite are drastically reduced at higher gigahertz frequencies. The permittivities, however, can be enhanced by appropriate choice of composition and processing temperature. In the present ferrite composition, silicon content is taken in excess so as to convert some of the Fe3+ ions to Fe2+ ions. This conversion has been shown to enhance EM and absorption properties. Mössbauer spectroscopy on the samples establishes that addition of excess Si4+ converts some of the Fe3+ to Fe2+. The sintered ferrites have shown resonance phenomena, but the composites do not. The EM parameters ε′, ε″, μ′, and μ″ were measured using a vector network analyzer (Agilent, model PNA E8364B). These measured EM parameters were used to determine the absorption spectra at different sample thicknesses based on a model of a single layered plane wave absorber backed by a perfect conductor. The sintered ferrite composition (x=0.9 and y=0.05) showed the best absorption properties [a minimum reflection loss of −17.7to−14.3dB over the whole frequency range of the X band (8.2–12.4) for a sample thickness of just 0.8mm], and it is used in the composite absorbers in powder form along with other constituents. The optimized composite absorber has shown dielectric constant ε′∼11.5, dielectric loss ε″∼2.3, and a minimum reflection loss of −29dB at 10.97GHz with the −20dB bandwidth over the frequency range of 9.7–12.2GHz for a sample thickness of 2.0mm. The magnetic parameters μ′ and μ″ for the composite remained nearly 1 and 0, respectively, throughout the measured frequency range. Both sintered ferrite and composite absorbers can fruitfully be utilized for suppression of electromagnetic interference and reduction of radar signatures (stealth technology).

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Barium titanate nanoparticles with an average size of <100 nm were added to poly(vinylidene fluoride‐trifluoroethylene) copolymer in varying concentrations (0.2, 0.4, 0.6, and 0.8 wt%) in liquid phase under bath sonication and annealed at 120°C for 2 h. The Fourier transform infrared spectroscopy, X‐ray diffraction, Raman spectroscopy, and Differential scanning calorimetry studies reveals an increase in the β‐phase content of the nanocomposite, which is a promising inference for the increased ferroelectric property of the material. Scanning electron microscopy and Atomic force microscopy was used to study the surface topography of the spin coated thin films. Polarization–electric field studies clearly indicating the enhanced ferroelectric nature of optimized concentration with highest remnant polarization. All these results nominate this polymer nanocomposite as a promising material for ferroelectric applications like nonvolatile memory devices. POLYM. COMPOS., 38:1655–1661, 2017. © 2015 Society of Plastics Engineers

In the present study, coating formulations based on carbon nanoparticle (125-150 nm) and two component polyurethane resin [Polyester polyol-8 and hexamethylene diisocyanate [C 8 H 12 N 2 O 2 (NCO-(CH 2 ) 6 -NCO)] have been prepared in concentration of 5,6,7,8, 9 and 10 g of carbon black in 100 ml of polyurethane solution and was applied on cotton fabric adopting knife over roller coating technique. The coated fabrics were evaluated for surface resistivity and relevant microwave properties i.e. permittivity, scattering parameters, reflection, transmission, absorption, reflection loss and electromagnetic interference shielding in HVS free-space microwave measurement system. It is observed that increasing the carbon content increases the permittivity values and decreases the impedance. It is seen that with increase of carbon content up to 7 g, absorption increases due to increase of permittivity while with further increase of carbon content from 8 to 10 g, absorption decreases due to increase of conductivity and thereby increased reflection. The coated fabric at 6.55 wt% carbon and 93.45 wt% PU in thickness of 1.3 mm has shown about 46% absorption, 29.49% transmission and 24.5% reflectance in X (8.2-12.4 GHz) and Ku (12-18 GHz) frequency band. When electrical thickness of coated fabric equals /4, a peak of reflection loss is observed due to Salisbury absorption mechanism. Highest reflection loss of -31.39 dB at 17 GHz, more than 20 dB in bandwidth of 16-18 GHz and more than 10 dB in entire Ku-band is