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http://www.scielo.br/rss.php?pid=2179-107420140002&lang=pt
vol. 13 num. 2 lang. pt<![CDATA[SciELO Logo]]>http://www.scielo.br/img/en/fbpelogp.gif
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<![CDATA[<b>Multiband frequency selective surfaces with a modified multifractal cantor geometry</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200001&lng=pt&nrm=iso&tlng=pt
Self-affine property of a modified multifractal Cantor geometry is exploited to design frequency selective surfaces (FSS) with multiband response. The main advantage of the proposed structure is to design multiband FSS with multiple frequency ratios between the adjacent bands and easily-built structures. In addition, the proposed structure increases the degree of freedom in design of multiband FSS response according to the number of fractal iterations. The validation of the proposed structure was initially verified through simulations in Ansoft Designer 3.5 and then a prototype was built with a validation purpose.<![CDATA[<b>QoS management in smart grids</b>: <b>a Markovian approach</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200002&lng=pt&nrm=iso&tlng=pt
In Smart Grids, a variety of new applications are available to users of the electrical system (from consumers to the electric system operators and market operators). Some applications such as the SCADA systems, which control generators or substations, have consequences, for example, with a communication delay. The result of a failure to deliver a control message due to noncompliance of the time constraint can be catastrophic. On the other hand, applications such as smart metering of consumption have fewer restrictions. Since each type of application has different quality of service requirements (importance, delay, and amount of data to transmit) to transmit its messages, the policy to control and share the resources of the data communication network must consider them. In this paper Markov Decision Process Theory is employed to determine optimal policies to explore as much as possible the availability of throughput in order to transmit all kinds of messages, considering the quality of service requirements defined to each kind of message. First a non-preemptive model is formulated and after that a preemptive model is derived. Numerical results are used to compare FIFO, non-preemptive and preemptive policies.<![CDATA[<b>Hardware embedded fiber sensor interrogation system using intensive digital signal processing</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200003&lng=pt&nrm=iso&tlng=pt
The description of an interrogation system for fiber Bragg grating sensors is reported. The full implementation in hardware of the required signal processing is proposed and made publicly available. The hardware description is implemented in a field programmable gate array (FPGA) development kit and the processing units allow one to control an optoelectronic interrogation system that uses the tunable filter method. Since the signal that drives the used Fabry-Perot filter (FFP) using a digital-to-analog converter (DAC) requires the generation of a triangular/saw-tooth waveform, the non-linear behavior of the DAC is compensated with a new methodology in this application using FPGA. When it operates controlled by a personal computer, off-board additional adaptive signal processing is used to suppress optical interference in an innovative way while removing undesired distortions in the signals caused by reflections in the optical circuit.<![CDATA[<b>A comparative analysis of cylindrical CFS-PML ABC for finite volume simulations in the frequency domain</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200004&lng=pt&nrm=iso&tlng=pt
A comparative analysis of two cylindrical complex-frequency-shifted perfectly matched layers (CFS-PML) absorbing boundary condition (ABC) for bi-dimensional (2-D) finite-volume (FV) simulations in the frequency domain is presented. The impact of CFS-PML parameters on the wave absorption, as well as on the condition number of the associated system matrix is investigated by comparing the performance of two PML loss profiles, viz., polynomial and geometric grading. FV-CFS-PML results are validated against analytical solution. Numerical results show that inclusion of a CFS-PML within the FV computational domain increases the condition number of the system matrix and therefore the use of CFS-PML 3-D FV simulations is limited.<![CDATA[<b>An efficient indoor ray-tracing propagation model with a <i>quasi</i>-3D approach</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200005&lng=pt&nrm=iso&tlng=pt
This paper presents an indoor propagation model that uses image-based ray-tracing with a quasi-3D approach. A fast 2D algorithm finds the most relevant rays lying in the horizontal plan of the indoor environment. Then, every path is converted into five rays that lie in the vertical plane. As a consequence, the third-dimension effect is considered in the field computation. Comparisons were made with measurements for a typical indoor scenario and the quasi-3D approach results showed to be as good as the results obtained by a full 3D ray-tracing tool. With this approach, it is possible to have a computational cost comparable to that of a 2D algorithm, without significant impairment in the accuracy compared to results obtained with a 3D tool.<![CDATA[<b>Design of a novel dual</b>: <b>band planar inverted F - antenna for mobile radio applications</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200006&lng=pt&nrm=iso&tlng=pt
The design of a novel compact dual band PIFA (Planar Inverted F-Antenna) as an embedded antenna is reported in this paper for mobile radio applications. The new shorted planar antenna is realized using copper sheet of thickness 1mm and air as the dielectric substrate. The radiating patch consists of a branch line slit to reduce the size of the antenna having a ground size of 36 x 80 mm2. It can be used in internal mobile antennas for applications in GSM band, GCV (1.85 - 1.99GHz), PCS - 1900, IMT-2000 and UMTS 2100 networks. The simulations are done using the Ansoft High Frequency Structure Simulator (HFSS) software tool. The two operating frequency ranges obtained have good matching and radiation characteristics. The simulated results are well supported by measured results of the prototype of the antenna fabricated.<![CDATA[<b>A new microstrip diplexer using open-loop resonators</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200007&lng=pt&nrm=iso&tlng=pt
In this paper, a new microstrip diplexer using open loop resonators with compact size and high isolation is designed and fabricated for the WLANs (IEEE 802.11b/g at 2.4 GHz and IEEE 802.11a at 5.2 GHz) applications. The diplexer is formed by two dual-mode band pass filters (BPFs) using an asymmetric fork-form feed line and two open loop resonators. The diplexer has less than 3 dB insertion loss and the isolation between the two channels is more than 25 dB. Furthermore, the proposed diplexer shows several transmission zeros beside the pass bands which improves the selectivity of the BPFs and thus improves the isolation between lower and upper channel filters and achieves a significant attenuation of the undesired harmonics. The electrical performances of the diplexer are investigated numerically by using Momentum integrated in ADS Agilent and CST microwave software. Good agreement between the simulation and measurement results is achieved.<![CDATA[<b>Experimental-based subsystem models for simulation of heterogeneous optical networks</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200008&lng=pt&nrm=iso&tlng=pt
This work presents and analyzes experimental-based subsystem models for Erbium doped fiber amplifiers (EDFAs) and wavelength selective switches (WSSs) under operation in a metropolitan optical network testbed. Firstly, the performance of the EDFAs and two gain control types are analyzed in a heterogeneous experimental setup with lightpaths modulated at 10G/100G/200G. Secondly, the WSS optical shape filter is experimentally characterized. Subsequently, simulation models are proposed accordingly to the experimental data obtained from the experimental setups. Results of output power and spectrum shape for both amplifiers under test showed good agreement between simulation and experiment. In addition, the optical signal-to-noise ratio (OSNR) for all channels was also analyzed and it was obtained error values bellow 1 dB, which are within an acceptable error margin. The developed sub-system models will provide greater flexibility to simulate different network scenarios and enable the development and validation of future optical network intelligence algorithms.<![CDATA[<b>Analysis of electronic structure of boron nitride nanotubes with different positions of intrinsic impurities</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200009&lng=pt&nrm=iso&tlng=pt
The pristine boron nitride nanotubes have a large direct band gap around 5 eV. This band gap can be engineered by doping. We investigate electronic structure of the doped hexagonal boron nitride (5,5) nanotubes using the linearized augmented cylindrical wave method. In particular, this work focuses on systematical study of the band gap and the density of states around the Fermi-level when the nanotubes are doped by intrinsic impurities of two substitutional boron atoms in a super cell and a comparative analysis of the relative stability of three structures studied here. This corresponds to 3.3% of impurity concentration. We calculate 29 configurations of the nanotubes with different positions of the intrinsic impurities in the nanotube. The band gap and density of states around the Fermi level show strong dependence on the relative positions of the impurity atoms. The two defect sub bands called Dπ(B) appear in the band gap of the pristine nanotube. The doped nanotubes possess p-type semiconductor properties with the band gap of 1.3-1.9 eV.<![CDATA[<b>Finite element analysis of hybrid excitation axial flux machine for electric cars</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200010&lng=pt&nrm=iso&tlng=pt
This paper presents a FEM analysis of a hybrid excitation brushless axial flux machine (HEBAFM) for traction electric vehicle purposes in order to compare with the results from an analytical method used to determine the flux densities in each part of the machine. The magnetic quantities of the proposed topology were investigated in order to obtain a satisfactory level of flux densities avoiding a possible saturation of the material. Keeping the magnetic induction under the saturation point, it will be feasible to increase the speed beyond the rated speed. The results from using the analytical method as well as via FEM simulation analysis presented a good approximation and are shown at the end of this paper.<![CDATA[<b>Study on radial suspension forces of bearingless permanent magnet slice motor based on accurate inductance model</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200011&lng=pt&nrm=iso&tlng=pt
An accurate mathematical model of radial suspension forces for a bearingless permanent magnet slice motor (BPMSM) is of great significance to levitate the rotor stably and to improve the control accuracy of radial suspension force. In this paper, after a brief introduction on the suspension principle of the BPMSM, the accurate inductance model of two sets of stator windings (torque windings and bearing windings) is deduced. Based on the accurate inductance model and taking rotor eccentricity into account, a complete and precise mathematical model of radial suspension forces of the BPMSM is obtained. In order to confirm the validity and feasibility of this mathematical model, the experiments are carried out on a 4kW prototype of the BPMSM. The experimental results show that the control system designed by using this method has high control accuracy of radial suspension force, strong capability of resisting disturbance, and good static and dynamic performance.<![CDATA[<b>Modified rain attenuation prediction method considering the effect of wind direction</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742014000200012&lng=pt&nrm=iso&tlng=pt
The method currently recommended by the ITU-R for the prediction of rain attenuation in terrestrial line-of sight links considers an equivalent path length over which the rain intensity is assumed to be constant. In other methods, the spatial and temporal variations of the rainfall rate along the path are characterized by an effective rainfall rate that is dependent on the actual path length. Based on experimental measurements, this paper presents a modified effective rainfall rate method that includes the prevailing wind direction during rainy conditions as an additional parameter for the prediction of rain attenuation. The wind direction, which can be obtained from meteorological databases with global coverage, is shown to significantly improve prediction accuracy.