Resumo em Inglês:

The study presented in this article is dedicated to the backfire disk-on-rod antennas fed by a dipole or crossed dipole. For short, these are herein called backfire antennas. Backfire antenna constructions with different configurations of the big reflector are considered. The influence of the feed location in the backfire antenna construction upon the antenna characteristics is also examined. The studies were carried out with a corrugated-rod (disks attached to a metal rod) surface-wave structure. The results obtained may be applied to other types of surface-wave structures, such as dipole ar-ray, dielectric rod or dielectric-covered metal rod. The lengths of the investigated antennas ranged between 2λ and 4λ. The design carried out in these investigations may be used for creation of high efficiency backfire antennas.

Resumo em Inglês:

In this experimental study a novel design has been developed to improve the antenna parameters in terms of impedance bandwidth and radiation properties. A 4-element rectangular array antenna (refereed as antenna 1) operating in the range of 10 to 16 GHz with multi bands is used as a reference antenna. The impedance bandwidth and other radiation properties have been enhanced by using defected microstrip structure (DMS) and defected ground structure (DGS). This study is further extended to 8-element array. The design consideration and experimental results of the proposed antennas are presented and discussed.

Resumo em Inglês:

An alternative technique that uses a flame-brush at high temperature to enhance UV light photosensitivity in an optical fiber is described. An extreme low-cost air aspirated propane-butane mini-torch is used, which produces a lower temperature flame than the one in the flame-brush original technique. It is shown that this change in the previous technique is also capable of improving photosensitivity and allowing the fiber Bragg grating imprinting process to be accelerated. Since the flame-brush photosensitivity enhancement process is designed to operate in an automated fiber taper rig, the process was evaluated in optical fiber tapers with different diameters. In this case, changes in photosensitivity are observed in the tapers in addition to the intrinsic photosensitivity occurring in the pristine fiber without being tapered.

Resumo em Inglês:

In this paper a highly polarization maintaining birefringent photonic crystal fiber at telecommunication window is reported via Full-Vectorial Finite Element Method (FV-FEM). By taking triangular lattice of three ring hexagonal structure PCF with suitable designing parameters such as symmetrical elliptical hole along radial axis of ellipticity a/b=5µm, air hole diameter d=1µm and pitch Λ=2.3µm, high birefringence (2.437×10-3) with small effective mode area(9.47µm²) and beat length (0.64cm) are found at wavelength 1.55µm.

Resumo em Inglês:

This paper presents an evaluation of the phase shifting excitation and load effects in a Transmission Line Exciting Chamber. This chamber is suggested as an alternative for immunity tests because of the restrictions related to canonical chambers. Here, two methods are used to calculate the E-field: a semi-analytic approach and a numerical one. The semi-analytic method is based on the modal expansion while a software is used for numerical simulations. The results regarding the E-field profile and the related statistical indexes of merit are presented and used to evaluate the chamber performances. Experiments were also conducted in order to evaluate the chamber.

Resumo em Inglês:

A compact CPW-fed ultra-wideband antenna with dual band-notch characteristic is presented. Two notched frequency bands are obtained by embedding two U-shaped slots in the radiation patch and a rectangle slot in the ground plane. The two notched bands can be controlled by adjusting the length of the responding slots. The proposed antenna is successfully simulated, fabricated and tested. Experimental and numerical antenna shows that the proposed antenna with compact size of 21×28mm2, has an impedance bandwidth range from 3.1GHz to more than 11.0GHz for voltage standing-wave ratio less than 2, expect two notch band frequency 5GHz-6GHz for WLAN and 7.7GHz-8.5GHz for X-band for satellite communications in China.

Resumo em Inglês:

This work deals with numerical techniques to compute electrostatic fields in devices with rounded corners in 2D situations. The approach leads to the solution of two problems: one on the device where rounded corners are replaced by sharp corners and the other on an unbounded domain representing the shape of the rounded corner after an appropriate rescaling. Both problems are solved using different techniques and numerical results are provided to assess the efficiency and the accuracy of the techniques.

Resumo em Inglês:

Several methods have been proposed to evaluate theoretically and experimentally the performance of optically amplified direct-detection orthogonal frequency division multiplexing systems. In this paper, we review those methods, and highlight their main advantages and disadvantages.

Resumo em Inglês:

The transverse flux permanent magnet machines have become an interesting possibility for offshore wind turbines. These machines have the highest relation between electrical torque and weight of active materials. The pole pair modular construction could eliminate or lower the gear ratio used in conventional wind turbines. This paper presents a dynamic model of a wind turbine equipped with a transverse flux permanent magnet generator connected to a direct-current power system using a combination of 3D finite element generator model and an aerodynamic model. The results indicate that the model can give accurate response for steady-state operation and for wind speed variations.

Resumo em Inglês:

This paper presents a performance comparison between known propagation Models through least squares tuning algorithm for 5.8 GHz frequency band. The studied environment is based on the 12 cities located in Amazon Region. After adjustments and simulations, SUI Model showed the smaller RMS error and standard deviation when compared with COST231-Hata and ECC-33 models.

Resumo em Inglês:

This paper describes the development of Hg0.8Re0.2Ba2Ca2Cu 3O8.8 thick film prepared with a precursor Ba2Ca2Cu3O5+d thick film, which was layered by Laser Ablation technique on PrBa2Cu3O7 substrate. The precursor thick film was thermally treated under mercury atmosphere using an encapsulate quartz tube technique. DC critical current measurements below T C determined the thick film superconductor current critical density as a function of temperature. The general behavior of the critical current density as a function of temperature confirms that the (Hg,Re)-1223 thick film has junctions type classified as superconducting-insulate-superconducting (SIS). After the critical current test the superconductor thick film has not shown any degradation or stoichiometry loss and its critical temperature has not changed after the test. Taken into account the critical current value of thick film as compared with the bulk sample, it was suggested that the procedure described here can be applied to build most electronic-type applications based on (Hg,Re)-1223 ceramic thick film.

Resumo em Inglês:

This paper presents the results of measurements and simulations of the characteristics of 900 MHz band radio propagation channels in a tunnel environment. The simulations were made using the FDTD method (with companion UPML) and measurements made use of the swept frequency technique. Another method, the metaheuristic Simulated Annealing, was implemented for estimating the values of characteristic parameters of materials. The FDTD code was reformulated for use with CUDA with the objective of decreasing program running time.

Resumo em Inglês:

The aim of this paper is to present and validate rain attenuation time series synthesizers relying on the Maseng-Bakken principle for terrestrial links in tropical areas. Data obtained in experimental measurements at four links operating at 15 GHz in São Paulo, Brazil, are used to parameterize the synthesizers. Two models are tested with respect to long-term statistics including cumulative distributions of rain attenuation, fade durations and fade slope.

Resumo em Inglês:

This paper presents a qualitative analysis of the impact caused by fiber propagation effects and by a cascade of optical filters, designed for 10 Gb/s NRZ OOK transmission, and optical amplifiers on a 20 Gb/s NRZ OOK optical signal traveling a 390 km fiber link. The choice for such bit rate and modulation format has been driven by the 50 GHz bandwidth of the filters (in the ITU DWDM grid) and by simplicity and low cost, respectively. The system, investigated experimentally and numerically, comprises 4 spans of standard fiber and a concatenation of 7 dispersion compensating modules, 4 wavelength selective switch reconfigurable optical add and drop multiplexers, 9 erbium-doped fiber amplifiers and 1 WDM-DEMUX (> 75 GHz bandwidth). We demonstrate the feasibility of such bit rate upgrade in a cost-effective network planning strategy, which may be more adequate for regions where the demand for bandwidth do not require a jump to higher capacities (i.e. 40 and 100 Gb/s), thus allowing for reusing the 10 Gb/s installed infrastructure.

Resumo em Inglês:

This paper evaluates several signal processing techniques for optical dual-polarization quadrature phase-shift keying (DP-QPSK) coherent receivers, using offline post-processing of experimental data. In addition to electronically separating the two polarization multiplexed signals, the investigated signal processing algorithms also compensate for chromatic dispersion (CD) and polarization mode dispersion (PMD). In particular, we investigate two distinct architectures: 1) Constant modulus algorithm (CMA) equalization followed by feedforward phase recovery. 2) Decision-directed least mean square (DD-LMS) equalization combined with decision-directed phase recovery. The interplay of both architectures with bulk dispersion compensators and carrier recovery algorithms is also analyzed.

Resumo em Inglês:

This paper presents an encoding scheme adapted for Fiber Bragg Grating (FBG) optimization using metaheuristics. The proposed encoding scheme uses spline approximations in order to build softened refractive index profiles from few encoded parameters. This approach is suitable for Fiber Bragg Grating (FBG) synthesis because it ensures both the reduction of the problem dimensionality and the respect of important restrictions associated to the FBG manufacture. Simulations are shown where an ES using the spline encoding was able to converge faster and produce more interesting filters, when compared with conventional encoding schemes.

Resumo em Inglês:

This work presents a technique to characterize the errors that occur in the process of manufacturing into electromagnetic simulations of microwave devices. The procedure combines the unscented transform (UT) with simulations. The use of the UT allows efficient use of computational resources for the characterization of the random variables modeling the uncertainty. The technique was validated with the simulation, construction, and test of several sets of identical microstrip filters with very good results. Although the combination of UT and electromagnetic simulators was presented for microstrip filters, it can also be used for different types of microwave devices.

Resumo em Inglês:

Despite its robustness the Switched Reluctance Motors (SRMs) present some inconvenient drawbacks as a major torque ripple, vibration and acoustic noise when compared to other types of motors. These characteristics are usually related to factors such as the salient poles in the stator and in the rotor, the switched feeding and the control strategy imposed by the electronic converter. In this paper a Special Switched Reluctance Motor for fractional horsepower and high speed hand tool was studied in order to minimize its vibration and torque ripple characteristics. This task was accomplished by the development of a simple and flexible motor drive and the combination of two different commutations strategies: the Three Level Control and the Single Pulse with Overlapping Phase Current. The SRM prototype and its drive were constructed and submitted to several tests with the proposed commutation strategies. In the frequency domain the strategies results were considered satisfactory.

Resumo em Inglês:

In this work, the electrical signals obtained by application of microwaves in chemical and bone tissues are analyzed and classified using techniques of signal processing and pattern recognition. For this, Wavelet Transform is applied as a method to extract relevant features of signal and KNN is used as a classification technique. The results showed that microwave signals can be analyzed using Wavelet Transform, which can be used to reconstruct the signals with minimal error rate and KNN showed satisfactory results.

Resumo em Inglês:

In this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.

Resumo em Inglês:

The production of magnetic forces in a magnetic actuator is the focus of the present analysis. Magnetic circuit analysis is used to investigate the direction as well as the expected order of magnitude of the force that attracts the armature into the central portion of a stationary core. A sequence of finite-element based solutions is used to investigate magnetic saturation and to determine the force-displacement characteristic. The analytical approach is based on the principle of virtual work and Ampère's law. The force calculations based on numerical field solutions employ the methods of weighted Maxwell stress tensor and the classical virtual work. The more accurate field-derived solutions are used to explain the limitations of the analytical calculations. At the end, an alternative approach to compute the force numerically is proposed. This method is based on the principle of virtual work, but only one field solution is required.

Resumo em Inglês:

Fiber-To-The-Home (FTTH) technology has been significantly implemented in access networks, providing very high data rates transmission and a variety of digital content to subscribers. It involves an optical cable link being installed between the building entry point and each subscriber with the Multiple Dwelling Units (MDUs), i.e. flats and apartments. In other words, optical cable has to lie fairly straight to carry a strong signal, since typically is necessary to bend, twist and turn the lines in and out of tight corners without degrading the link connection. In this paper we propose the use of Hollow-Core Photonic Crystal Fiber (HC-PCF) for FTTH applications. It is presented an experimental analysis of the macrobending effects in a HC-PCF based on a comparison with traditional fibers and by following the ITU-T G.657B standard recommendations. We observe this fiber, with only 6.5 µm core, is bending loss insensitive, even at extremely small bending radius of 2 mm, in which it presents a loss of only 0.58 dB.

Resumo em Inglês:

The quality of the optical fiber infrastructure is directly related with the strength of the fiber polymer coating. In this work we have studied the effect of maritime environment in the aging of optical fibers. The results show a decay rate of 0.00766±0.00065 GPa.day-1 for a 35g/L NaCl solution and of 0.01101±0.00133 GPa.day-1 for a 250g/L NaCl solution. The Boltzamann fit presented corroborates the experimental data, which shows that the aging transition period appears sooner for more concentrated solutions. The microscopy and SEM analysis performed confirmed the degradation condition of the fibers under study.

Resumo em Inglês:

This article introduces a procedure for determining the optimum design of pyramidal horn antennas. The efficiencies and phase errors in the optimum design are variables and depend on the design requirements. New equations are proposed for the optimum design, which can be solved numerically or analytically.

Resumo em Inglês:

In this paper, the boundary condition characteristic equation of the anisotropic-dielectric-loaded corrugated guide are developed. Dispersion curves of hybrid modes generated by the characteristic equation are presented and discussed. This paper also presents a technique to reduce the relative permittivity and create uniaxial anisotropy from isotropic homogeneous dielectric.

Resumo em Inglês:

THz continuum spectral photometry has new and unique applications in different civil and military areas presenting a number of distinctive advantages on the well known microwaves or mid- to near-infrared technologies. THz sensing is essential to investigate the emission mechanisms by high energy particle acceleration processes. Technical challenges appear to diagnose radiation produced by solar flare burst emissions measured from space as well as radiation produced by high energy electrons in laboratory accelerators. THz filters and detectors have been investigated for the construction of solar flare high cadence radiometers to operate outside the terrestrial atmosphere. Experimental setups have been assembled for testing THz continuum radiation response from distinct detectors: adapted commercial microbolometer array, pyroelectric module, and opto-acoustic (Golay cell). The results permitted the final design of a THz double radiometer using Golay cells to be flown in stratosphere balloon missions.