Analytical prediction of resonant frequencies of annular stacked dielectric resonator antennas

The method of stacking dielectric resonators for designing multiband and wideband antennas has gained much attention in recent times. However, the existing works lack any theoretical framework for the prediction of resonant frequencies of such stacked structures. In this work, a formal analysis using a cavity model with the mode matching technique is presented to determine all the existing resonant frequencies of annular stacked cylindrical dielectric resonator antennas with and without air gap. The analysis is done separately considering the outermost sidewall of the stack as both perfect magnetic conductor and imperfect magnetic conductor. The theoretical findings are extensively validated against numerous simulations, as well as against a fabricated prototype. It is observed that the perfect magnetic wall condition provides results that are more accurate. The closed‐form equation derived in this work not only helps in accurately predicting the resonant frequencies but also reduces the run‐time manifolds compared to that of the existing trial and error based methods of design using software simulations.     

Goubau line based end‐fire antenna

This article proposes a simple and low profile planar Goubau line based end‐fire antenna. End‐fire radiation is achieved by modifying the Goubau line into inverted periodic arrangement of V‐shaped unit cells. Designed prototype is simulated and verified experimentally. Both the simulated and measured results are in good agreement. Proposed antenna radiates toward end‐fire direction between 7.8 and 8.3 GHz. The maximum gain of the antenna is obtained around 7.2 dBi. The average efficiency is observed 70% over the entire operating bandwidth. Proposed end‐fire antenna has a single metallic layer with simple configuration which is easy to fabricate and also easy to integrate with other electronics circuits. The proposed antenna can be used for satellite and RADAR applications.     

Implementation of enhanced forward pointer-based mobility management scheme for handling internet and intranet traffic in wireless mesh network

To implement WMN, IEEE 802.11s has been developed. The routing protocol for selecting a path between two mesh stations in IEEE 802.11s is hybrid wireless mesh protocol (HWMP). But mobility of external stations has not been considered in IEEE 802.11s. For handling movement of clients, many mobility management schemes have been proposed. Some of such schemes are: ANT, Mesh Mobility Management (M\(^{3})\), Infrastructure Mesh (iMesh), SMesh, MEsh networks with MObility management (MEMO), Wireless mesh Mobility Management (WMM), Static Anchor Scheme, Dynamic Anchor Scheme, LMMesh, Session-to-Mobility-Ratio based Scheme and Forward Pointer-Based Mobility Management Scheme (FPBR). But none of the schemes except FPBR have been integrated with IEEE 802.11s for providing mobility support to the external stations. FPBR has been proposed to enhance IEEE 802.11s for providing mobility support to external stations, but it can support internet traffic only. In WMN both internet and intranet traffic to and from the external station is important. In this paper, an improved version of FPBR named Enhanced FPBR (EFPBR) Scheme has been introduced to handle both internet and intranet traffic. Both EFPBR and HWMP have been numerically analyzed. HWMP and EFPBR schemes are simulated and the performances are compared. From the performance comparison, it can be observed that EFPBR performs better than that of IEEE 802.11s concerning throughput, end-to-end delay, routing overhead and average handoff cost. The number of route management packets transferred per handoff measured from numerical analysis and simulation has also been compared.     

Pressure drop and bubble-liquid interfacial shear stress in a modified gas non-Newtonian liquid downflow bubble column

A functional form of equation for predicting pressure drop in a modified non-Newtonian downflow bubble column has been formulated. The equation has been developed based on the bubble formation, drag at interface and the wettability effect of the liquid. Also the bubble-liquid interfacial shear stress in two-phase flow is analyzed and correlated with the dynamic, geometric and physical variables. The functional form of equation appears to predict the pressure drop satisfactorily for two-phase dispersed flow in the co-current modified downflow bubble column with carboxy methyl cellulose (CMC) solution in water with different concentrations.     

A first principle study of SO3 decomposition on silver nano-clusters: Implications toward hydrogen production

In this work, based on first principles density functional theory, we have investigated the interaction of SO₃ molecule on three different substrates; (i) clean Al₂O₃ surface (0001) (ii) an isolated Ag₆ cluster and (iii) Ag₆ clusters deposited on the Al₂O₃ surface. All calculations were carried out using the plane wave based pseudopotential method under the framework of density functional theory. For the clean Al₂O₃ surface, the SO₃ molecule was adsorbed in parallel orientation on the surface resulting in an elongation of the S–O bond from 1.44 to 1.52 Å with interaction energy of 1.67 eV. In contrast, the interaction of SO₃ with Ag₆ was found to be weak with 0.4 eV interaction energy and 1.47 Å as the largest S–O bond length. Remarkably, when SO₃ molecule interacted with Ag₆ cluster deposited on the Al₂O₃ support, the binding was found to be higher than both Al₂O₃ and Ag₆ clusters in their isolated state. In particular, upon adsorption of SO₃ on Ag₆/@Al₂O₃, the S–O bond length was found to increases from 1.44 to 1.64 Å and the interaction energy was estimated to be 2.00 eV. As the bond elongation bears the signature of bond weakening, a comparison of the above three results clearly suggests that the dissociation barrier of S–O bond on the Ag₆@Al₂O₃ support will be significantly lower than that on the isolated Ag₆ or Al₂O₃ surface. The nature of chemical interaction of SO₃ on these three systems has been discussed based on the electronic density of states analysis.     

Indication of formation of charge density waves in silver nanoparticles dispersed poly(methyl methacrylate) thin films

Silver nanoparticles of various sizes have been prepared through the chemical synthesis and dispersed into poly(methyl methacrylate) (PMMA) matrix resulting in solution cast nanocomposite thin films. For characterization of the films, UV–vis absorption spectroscopy and FESEM were used. Observed blue shift of the surface plasmon absorption band position of the nanocomposite films is an indication of gradually smaller size of the silver nanoparticles that have been dispersed into the PMMA matrix. Dark current (I_d) vs. time profiles and the fluctuations in current–voltage characteristics for the PMMA films with dispersed silver nanoparticles were found to depend on the position of surface plasmon absorption band. Results of electrical studies have been found to be temperature- and voltage-dependent manifesting nonlinear nature of the I_d which may be an indication of formation of charge density waves in the silver nanoparticles–PMMA nanocomposite films. The increase in the standard deviation in I_d (calculated from the I_d vs. time profiles) for the silver nanoparticles–PMMA nanocomposite films may be due to the increase in the plasmon oscillations. Thermal hysteresis has been observed in the PMMA films and in the silver nanoparticles–PMMA nanocomposite films. Results on the observed electrical properties have been discussed in the light of interaction of silver nanoparticles with PMMA matrix, structural reorientation of PMMA, role of electric field in the manipulation of silver nanoparticles in the polymer matrix etc.     

Analytical Performance Evaluation of a STBC Coded OFDM FSO Communication System over Turbulent Atmospheric Channel

Journal of Communications Technology and Electronics - An analytical approach is presented for an optical IM/DD system with STBC coded OFDM RF subcarrier modulation over a free space optical...     

Structural,electronic and thermodynamic properties of ZrCo and ZrCoH3: A first-principles study

The ZrCo intermetallic is considered to be strategically important for hydrogen isotope storage and its use in the International Thermonuclear Experimental Reactor (ITER) system. Here we report the structural, electronic and thermodynamic properties of ZrCo and ZrCoH₃ using the first-principles approach. The calculations are performed using a plane-wave based pseudo-potential approach under the framework of spin-polarized density-functional theory. The ground state properties like lattice constants, bulk moduli, and enthalpy of formation have been determined by optimizing the atomic and electronic structure of ZrCo and ZrCoH₃ compounds. From the total energy calculations, the enthalpy of formation of ZrCoH₃ from ZrCo is estimated to be −91 kJ/mol H₂ at 0 K. Both lattice parameters and formation energy are found to be in good agreement with their corresponding experimental values. The nature of chemical bonding in ZrCo and ZrCoH₃ has been analyzed from the electronic density of states spectrum of the constituent materials.     

Analysis of intermittent timing fault vulnerability

Continuous scaling of transistor feature size rapidly increases the effect of intermittent faults. These faults manifest as timing violations due to the combined effects of process variation, circuit wear-out, and variation in environmental conditions. In this paper, we combine all critical sources of intermittent faults in a comprehensive framework. Our experiments with the MIPS-789 processor reveal that at the 22nm technology node, the combined effect of all the factors can degrade the delay by 2.5X. Such gross delay degradation extending more than two cycles can render many recently proposed time borrowing techniques ineffective. We analyze three architectural techniques to mitigate intermittent faults and evaluate them using full system architectural simulation.