Design of an integrated UWB antenna with dual band notch characteristics

A miniaturized couple-line-fed planar ultra-wideband (UWB) antenna is proposed, which has a dual band-notched characteristic as well as two integrated monopoles. Narrowband notches are generated at frequencies of 3.5 GHz and 5.5 GHz using independently controlled bent resonators, whereas the monopoles are designed for radiation at 900 MHz and 2.4 GHz. The proposed design is simulated with full wave solvers and verified with measurements. A good agreement is observed between the simulations and measurements for the antenna's return loss, gain and radiation pattern performances.     

A wide-ranging review on Nasicon type materials

Nasicons (sodium super ion conductors) are a class of solid electrolytes. Their structure, compositional diversity, evolution, and applications are reviewed. A wide range of materials is considered based on crystalline and glassy Nasicon compositions.     

Synthesis and characterization of morphologically different high purity gallium oxide nanopowders

High purity gallium oxide nanopowders have been synthesized by using a simple precipitation technique with calcination at elevated temperature. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as β-Ga₂O_3. Elemental quantification (stoichiometry) of Ga₂O₃ was also examined from the X-ray energy dispersive analysis (EDAX). Based on the recorded Fourier Transform Infrared (FTIR) spectrum of Ga₂O_3, the IR bands due to Ga–O bond and crystal lattice vibrations have been identified in the wavenumber range 400–4,000 cm⁻¹. From the measured SEM images, it is obvious to notice that the pH value has been playing a dominant role in obtaining morphologically different gallium oxide nanopowders. Thermogravimetric analysis reveals 8.3% of weight loss when the sample was heated to the temperature of 1,100 °C from the room temperature, which also shows a crystalline phase transformation. It is very interesting to report that a broad blue emission at 455 nm has been measured from the synthesized gallium oxide nanopowders.     

Design of Ultra-Wideband Monopulse Receiver

In this paper, we propose a novel amplitude-comparison monopulse receiver architecture for ultra-wideband radars. This monopulse receiver consists of four ridged-horn antennas placed in a square-feed configuration, a comparator circuit that generates the monopulse sum and difference signals, cross-correlation receivers that detect the monopulse signals, and an amplitude-comparison monopulse processor that determines the target's angular position. The derived monopulse sum and difference signals are verified through measurements. The derived sum and difference patterns are compared with measured patterns, and they show good agreements-measured 3-dB beamwidth=6.4deg(derived=6deg), measured unambiguous tracking range=plusmn5deg(derived=plusmn5deg), and measured sum pattern sidelobe level=-6 dB (derived=-8 dB)     

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10⁻² and 2.4 × 10⁻² S/cm at 700 °C and 800 °C respectively.     

Empirical approach to develop a multilayer icebonded abrasive polishing tool for ultrafine finishing of Ti-6Al-4V alloy

This paper covers the development of a multilayer icebonded abrasive polishing (IBAP) tool for multistage polishing of Ti-6Al-4V alloy specimens based on a systematic study that determined the number of layers, thickness of each layer, and the type, size and concentration of abrasives in each layer. Based on this study, a three-layered IBAP tool with the bottom layer consisting of soft aluminum oxide abrasives of 3?µm size with 5% concentration, the middle layer with moderately hard silicon carbide abrasives of 8?µm size with 10% concentration and the top layer with hard boron carbide abrasives of 15?µm size with 30% concentration was formulated for ultrafine finishing of Ti-6Al-4V alloy specimen in a single setup. The performance of the three-layered IBAP tool assessed in terms of finish and morphology over the work surface showed 81% improvement in surface finish, showing its effectiveness over a single-layered IBAP tool. Polishing studies have clearly demonstrated the generation of ultrafine surfaces, yielding a finish of 37?nm while the morphological studies on the polished surface have shown a nearly scratch-free surface on the Ti-6Al-4V alloy.     

Low sintering effect on structural,electrical and magnetic properties of rare-earth metal ion Er3+-substituted nickel–zinc spinal ferrites

Journal of Materials Science: Materials in Electronics - The nano-crystalline particles of erbium-substituted Ni–Zn ferrites with compositional formula Ni0.7Zn0.3ErxFe2?xO4...     

Development of non-perfluorinated hybrid materials for single-cell proton exchange membrane fuel cells

Development of low temperature fuel cells that operate under 100 °C are needed to reduce the costs, to design a class of hybrid membranes and to construct various structures of membrane-electrode-assembles (MEAs) for proton exchange membrane fuel cells (PEMFC). In this work, PVA/PMA/SiO₂ hybrid composite membranes were synthesized and their conductivities were determined by impedance measurements. We found a maximum conductivity value of 4.2 × 10⁻³ S/cm at 80 °C and 100% relative humidity (RH). A fuel cell test evaluation for various MEAs was conducted by the potentiodynamic analysis and the current density values were determined from the current–voltage (I–V) curves. A maximum current density of 635 mA/cm² was obtained at 80 °C and 100% RH. To the best of our knowledge, this is the first time that a high current density of PVA-based electrolytes for PEMFCs operating at low temperature is reported. The structural characters were examined using of XRD and FTIR methods, and thermal properties were studied using DSC and TGA techniques and the results were discussed (cf. supplementation). The present study revealed that the single cell performance depends mainly on the temperature, relative humidity and chemical compositions of the membranes.     

Ferric oxide/date seed activated carbon nanocomposites mediated dark fermentation of date fruit wastes for enriched biohydrogen production

Biohydrogen production from biomass waste, not only addresses the energy demand in a renewable manner but also resolves the safe disposal issues associated with these biowastes. Also, scalable and low-cost techniques to enhance biohydrogen production have gained more attraction and are highly explored. In this research work, date-palm fruit wastes have been studied for their biohydrogen production potential using Enterobacter aerogenes by dark fermentation. Hydrogen yield and productivity were improved through the addition of iron oxide nanoparticles (Fe₃O₄ NPs) and its date seed activated carbon nanocomposites (Fe₃O₄/DSAC) to the fermentation media. Studies on discrete inclusions of these NPs showed that the appropriate dosage of NPs promoted, while higher dosages repressed the hydrogen production performance. Optimal dosage and fermentation time was observed as 150 mg/L and 24 h for both the additives. Fe₃O₄/DSAC nanocomposites showed better hydrogen production enhancement than Fe₃O₄ NPs. Maximum hydrogen yield of 238.7 mL/g was obtained for the 150 mg/L nanocomposites, which was 65.7% higher than that of the standalone Fe₃O₄ NPs and three folds higher than the yield of the control run without any NPs inclusion (78.4 mL/g). Metabolites analysis showed that the hydrogen evolution followed the ethanol-acetate pathway. Formation levels of longer chain propionate and butyrate co-metabolites were significantly low in the presence of Fe₃O₄/DSAC than Fe₃O₄. The carbon support in the nanocomposites acted as an adsorbent-buffer, which favored the medium pH in-addition to the stimulatory effects of Fe₃O₄ NPs. Cell growth and specific hydrogenase activity analysis were also performed to supplement the hydrogen production results. Gompertz and modified Logistic kinetic models were employed for kinetic modeling of experimental hydrogen production values. The Fe₃O₄/DSAC nanocomposites exhibited significant application potential for the production of biohydrogen from date fruit wastes.