We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Perfect metamaterial absorber.

The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites

Carbon (C) is a crucial material for many branches of modern technology. A growing number of demanding applications in electronics and telecommunications rely on the unique properties of C allotropes. The need for microwave absorbers and radar-absorbing materials is ever growing in military applications (reduction of radar signature of aircraft, ships, tanks, and targets) as well as in civilian applications (reduction of electromagnetic interference among components and circuits, reduction of the back-radiation of microstrip radiators). Whatever the application for which the absorber is intended, weight reduction and optimization of the operating bandwidth are two important issues. A composite absorber that uses carbonaceous particles in combination with a polymer matrix offers a large flexibility for design and properties control, as the composite can be tuned and optimized via changes in both the carbonaceous inclusions (C black, C nanotube, C fiber, graphene) and the embedding matrix (rubber, thermoplastic). This paper offers a perspective on the experimental efforts toward the development of microwave absorbers composed of carbonaceous inclusions in a polymer matrix. The absorption properties of such composites can be tailored through changes in geometry, composition, morphology, and volume fraction of the filler particles. Polymercomposites filled with carbonaceous particles provide a versatile system to probe physical properties at the nanoscale of fundamental interest and of relevance to a wide range of potential applications that span radar absorption, electromagnetic protection from natural phenomena (lightning), shielding for particle accelerators in nuclear physics, nuclear electromagnetic pulse protection, electromagnetic compatibility for electronic devices, high-intensity radiated field protection, anechoic chambers, and human exposure mitigation. Carbonaceous particles are also relevant to future applications that require environmentally benign and mechanically flexible materials.

A review and analysis of microwave absorption in polymer composites filled with carbonaceous particles

Temperature dependent microwave attenuation behavior for carbon-nanotube/silica composites

Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.

Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption

The effect of Co2+Ti4+ substitution on complex permeability, permittivity, and microwave absorption has been studied for [Ca(CoTi)xFe12−2xO19]96.0[La2O3]4.0 ferrite-epoxy composites, wherein x varies from 0 to 1.0 in steps of 0.2, in the frequency range from 8.0 to 12.4 GHz. The ferrites with x>0 exhibit significant dispersion in complex permittivity (e′−je″) with the maximum value of e″ observed for x equal to 0.2. The dispersion in complex permeability (μ′−jμ″) is not significant. The variations of reflection loss and percentage absorption have been studied as a function of frequency, Co2+Ti4+ content, and thickness of the absorber. A maximum reflection loss of 31.0 dB is obtained for composites with x equal to 0.2 and absorber thickness of 2.5 mm. The experimental values of the matching frequency and the matching thickness agree well with the theoretical values obtained from an impedance-matching solution map.

Complex permittivity, permeability, and X-band microwave absorption of CaCoTi ferrite composites

Relationship between structure and inhibition behaviour of quinolinium salts for mild steel corrosion: Experimental and theoretical approach

Aim: The aim of present study was to synthesize and characterize gold nanoparticles applicable in therapeutics and diagnostics tool for different diseases in particular for peste des petits ruminants (PPR). +3 0 Materials and Methods: Gold nanoparticles were synthesized by the reduction of Au (HAuCl ) to Au . For this purpose, the 4 reduction reaction between tetrachloroauric acid (HAuCl ) and trisodium citrate (Na C H O .2H O) was used in an aqueous 4 3 6 5 7 2 solution. The initial gold concentration, trisodium citrate concentration and temperature were changed and their effects on particle size and size distribution were observed. At the end of the reduction reaction, gold nanoparticles with narrow size distribution were obtained. Zeta sizer and transmission electron microscopy (TEM) were used to characterize and determine the size and size distribution of the synthesized gold nanoparticles. Results: In the present work optimal gold salt concentration, trisodium citrate concentration and temperature were found to be 0 20 mM, 1.5% and 97 C respectively. The morphology, size, and shape of synthesized gold nanoparticles were characterized by using spectrophotometry, transmission electron microscopy (TEM) and zeta sizer. In our study colloidal gold nanoparticle of 15-20 nm size were obtained. Conclusions: The uniform gold nanoparticles were synthesized by the citrate reduction method. The effects of various experimental parameters (Gold salt concentration, trisodium citrate concentration and mixing rate) on its size and size distribution at optimum pH and temperature were investigated. The gold nanoparticle synthesized by this method has been used for the preparation of gold-labeled lateral flow strip for peste des petits ruminants (PPR) diagnosis.

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Gold nanoparticle: synthesis and characterization.

The effect of Ni2+Ti4+ substitution on complex permeability, permittivity and microwave absorption has been studied for [Ca(NiTi)xFe12-2xO19]96.0[La2O3]4.0 ferrite–polymer composites, wherein x varies from 0.0 to 1.0 in steps of 0.2, in frequency range from 8.0 to 12.4 GHz. The ferrite-composites with x>0.0 exhibit significant dispersion in complex permittivity (e′-je′′) with maximum value of e′′ observed for x=0.6. The dispersion in complex permeability (μ′-jμ′′) is not significant and is attributed to the shielding effect of polymer matrix over the ferrite crystallites. The variation of reflection loss has been studied as a function of frequency (f), Ni2+Ti4+ content (x) and thickness of the absorber. A minimum reflection loss of −30.0 dB is obtained for composite with x=0.4 and an absorber thickness of 4.15 mm. The experimental values of the matching frequency and the matching thickness agree well with the theoretical values obtained by solving the equations numerically.

Praveen Singh

Papers

Complex permittivity, permeability, and X-band microwave absorption of CaCoTi ferrite composites

Relationship between structure and inhibition behaviour of quinolinium salts for mild steel corrosion: Experimental and theoretical approach

Gold nanoparticle: synthesis and characterization.

Microwave absorption studies of Ca-NiTi hexaferrite composites in X-band

Inhibition of mild steel corrosion by 1,4,6-trimethyl-2-oxo-1,2-dihydropyridine-3-carbonitrile and synergistic effect of halide ion in 0.5 M H 2 SO 4