Resumo em Inglês:

Abstract The authors utilized a heuristic shift-or-shrink method that is associated with the beam propagation method to design an optimal multisegment bent optical waveguide. By transforming the shape of each segment, the multisegment structure of the bent waveguide can be optimized. In addition to achieving maximal transmission efficiency, only four segments are sufficient to satisfactorily improve the transmission performance. Moreover, the optimal path of each of these multisegment bent waveguides remains similar to each other waveguide's optimal path even though the number of the segments increases.

Resumo em Inglês:

Abstract In this paper, a double layer stopband Frequency Selective Surface (FSS) for Ultra-Wide Band (UWB) applications is presented. The proposed FSS consists of two cascaded conventional FSS, one with double square loops and other with square loops. The − 10dB frequency band from 3.00 GHz to 11.64 GHz is achieved, with a fractional bandwidth of 149 %. Effects of angular stability and polarization independence over the frequency response are investigated and conclusions are presented. In order to show transmission performance, the FSS was simulated by ANSYS HFSS. The FSS shows angular stability and polarization independence in entire UWB band (3.10 – 10.60 GHz). A prototype was built and measurements were performed. A good agreement between simulated and measured results was observed.

Resumo em Inglês:

Abstract The energy demand by modern society grows every day that allied with sustainable development requires the use of alternative sources in the new energy matrix. In this context, the wind energy as source by using a doubly-fed induction generator stands out due to its operational savings but still faces some conflicts in its power control. This paper proposes a state feedback plus integral controller for rotor current control. In order to verify the controller operation, an electromagnetic finite element analysis simulation of the interior of the machine was carried out, assuring the non-saturation of the core, which would lead to a control instability and it can increase the machine losses. For this, a machine modeling was presented into state equations in order to establish a power control diagram. The results of electromagnetic simulation and the experimental bench results when united ensure the correct functioning of the proposed system and the satisfactory efficiency of the controller. In this way, it can be concluded that the use of this control technique in counterpart with the conventional PI increases the response time of the system without affecting the electromagnetic dynamics of the generator.

Resumo em Inglês:

Abstract This paper proposes an optimal design for a surface mounted permanent magnet synchronous machine (SM-PMSM) based on parametric optimization process to reduce the on-load Back-EMF distortions caused by an increase in the electromagnetic load and in the saturation. Unlike conventional methods described in the literature, the optimization approach proposed here accounts for the saturation effects, air gap flux density distribution and the evaluation of the on-load Back-EMF by means of finite element analysis, allied to the most recent on-load Back-EMF evaluation method, known as the Back-EMF MST (Maxwell stress tensor) method. Furthermore, the optimization process is performed considering either the machine's physical symmetry (based on pole numbers) and its nonevident symmetry (based on saturation effects and on the relevance of each tooth in the Back-EMF waveform), which is identified using the Back-EMF MST method. The proposed optimization process also analyzes different sets of variables based on symmetric and asymmetric tooth dimensions. The result is a machine with a reasonably improved design, higher average torque, lower torque ripple and smaller volume. In addition, the on-load Back-EMF is almost identical to the no-load one. Hence, the on-load cogging torque is almost identical to the no-load cogging torque.

Resumo em Inglês:

Abstract In this paper, the metamaterial based rectangular microstrip patch antenna is proposed and designed for THz applications. The circular split ring resonator is implemented as metamaterial. By incorporating metamaterial in the conventional microstrip patch antenna, the size is reduced and the performance of antenna is improved. The proposed antenna has the dimensions of 180 × 212 ×10 μm3 which is designed on Quartz substrate which is fed by microstrip line feed technique. Additionally, the performance of the metamaterial antenna is analyzed by varying unit cell gap size and thickness. The antenna resonates at 1.02 THz which gives the return loss of −65 dB. Thus, the proposed antenna can be utilized in THz region.

Resumo em Inglês:

Abstract This paper presents a bandpass filter based on a substrate integrated E-plane waveguide (SIEW) structure for wireless applications, at X-band. The SIEW geometry allows the development of new horizontally polarized filter topologies, unlike filter structures based on substrate integrated waveguide (SIW), which present vertical polarization (perpendicular to the ground plane). The simulation of the proposed SIEW filter is carried out using Ansoft HFSS software. To evaluate the performance of the proposed structure, the frequency behaviors of the scattering parameters are obtained for a horizontally polarized excitation. In the simulation, analyses are performed for the lossless and lossy (dielectric and metallic) cases, in order to compare the obtained results. The SIEW filter is fabricated and measured using a vector network analyzer (VNA). Measurement results are in agreement with simulation ones, validating the proposed filter design and topology. The fabricated prototype resonates at 10.54 GHz, with a bandwidth of 1.20 GHz, defined for a -3 dB transmission coefficient reference level. The SIEW filter structure is easy to design and manufacture and can be used in wireless communications systems that require components with ease integration into other planar structures.

Resumo em Inglês:

Abstract This work proposes the study of patch antennas with fractal slots. Initially, a 2.4 GHz microstrip antenna is designed. Then, the slots in the Koch fractals format are inserted with the iteration 0, 1 and 2. Similarly, it is expected that the antenna can be subjected to various functions in other applications. Simulations using CST STUDIO SUITE Student Edition software are shown, in addition to antenna measurements using the Network Analyzer.

Resumo em Inglês:

Abstract The Jiles-Atherton scalar hysteresis model presents five parameters used to represent the material tested and used to calculate the magnetic losses. This article presents a comparative analysis of the performance of two methods of identifying these parameters. In the first method, the equations of Jiles-Atherton were assembled into a single non-linear ordinary differential equation as a function of the variables of interest. An algebraic system of five equations with five unknowns is obtained by evaluating the non-linear ordinary differential equation in five points belonging to the branch of the experimental hysteresis loop. The parameters are obtained by solving this system of equations using the method of Non-Linear Least Squares (NLLS). In the second method, the inverse model of Jiles-Atherton is used to calculate the magnetic field H from the experimental values of magnetic induction B. Using the method of genetic algorithms (MGA), the objective function given by the sum of the relative error of calculated magnetic field and experimental magnetic field along the hysteresis loop is minimized. To validate methods the experimental curves were compared with calculated ones. When applying the methods, it was verified that NLLS besides providing more accurate results, it is faster when compared to MGA. In the MGA the convergence of the calculated magnitudes to the experimental magnitudes improves when one of the chromosomes of the initial population is the solution obtained applying NLLS.

Resumo em Inglês:

Abstract Starting from outdoor transmission, crossing vegetation, the wideband and narrowband characterization of the indoor mobile radio channel in the 700 MHz band is obtained from experiments carried out in the indoor environment of the Engineering building at Fluminense Federal University, and from the processed data, respectively, the power-delay profiles obtained permitted to calculate the time dispersion parameters and the envelope of the signal permitted to adjust probability density functions to the signal variability, concluding about the influence of vegetation on those characteristics.

Resumo em Inglês:

Abstract This paper presents the propagation channel characteristics of a digital TV single-frequency network (SFN) obtained by carrying out field measurements using two synchronized transmitters. The measurements are performed at 31 reception points using both a directive reception antenna, which is typical of fixed reception scenarios, and an omnidirectional antenna, which is used to receive mobile signals. The characteristic parameters of the channel are obtained, including the average delay, the root mean square (RMS) delay spread, and the Rician K-factor, which are important for the design of SFN systems. An empirical expression is obtained for the prediction of the RMS delay spread as a function of the K factor and the distances to the transmission antennas.