Abstract in English:Abstract In this work, a new method employs Bioinspired Computational (BIC) optimization from the genetic algorithm, bat algorithm, and flower pollination algorithm. Robust and accurate modeling of the input parameters adjusts the propagation models Stanford University Interim, Electronic Communication Committee, and Floating Interception that consider environments with characteristics specifically of urban regions in the Amazon. The lack of research related to the development of propagation models for Amazonian environments motivated this work. Thus, this application proves the effectiveness of using BIC techniques for modeling the communication channel. Measurement campaigns were carried out in the city of Belem, Brazil, for large-scale channel modeling on the frequencies of 1.8 and 2.6 GHz, belonging to the long-term evolution or fourth-generation mobile communications system (4G). After being adjusted by the optimum values calculated by the BIC techniques used, the models showed better results compared to modeling without optimization. Additionally, it was verified an error reduction of about 80% concerning the metrics root-mean-square error and standard deviation.
Abstract in English:Abstract In reconfigurable frequency selective surface, FSS, bias lines can suppress a resonant frequency. This is a disadvantage, as it reduces a FSS potential application. In this paper, a procedure to recover the suppressed resonant frequency is described. A FSS based on four arms star geometry is considered and its reconfigurability is achieved by the use of varactors, for which bias lines suppress the x polarization resonance. So, dipoles are added to the unit cell geometry recovering this resonance. In order to validate the proposed procedure, a reconfigurable FSS using the varactor SMV1231 (0. 466 pF ≤ Cv < 2. 35 pF) was fabricated and characterized. Numerical and measured results shown a good agreement, confirming that the FSS reconfigurability is preserved and the suppressed resonance recovered.
Abstract in English:Abstract This research presents the design and main electromagnetic characteristics of the novel compact microwave waveguide polarizer. The developed device's structure is based on a circular waveguide and anti-phase conducting posts located in it. The application of a circular waveguide instead of a square one allowed simple integration of a polarizer with corrugated horn antennas. The obtaining of required phase difference using a posts-based design provides the possibility of fine tuning of the developed circular waveguide polarizer after its manufacturing process. In addition, simultaneous adaptive operation at orthogonal circular and linear polarizations is available in the antenna system including a polarizer with posts. An automatic control of posts height must be applied in a waveguide in order to provide this option. Numerical simulation, optimization, manufacture and measurements of the polarizer's characteristics were carried out in the operating band 7.4-8.5 GHz. Measured characteristics proved that the suggested circular waveguide polarizer provides good matching and polarization performance. Developed circular waveguide polarizer can be integrated in corrugated horn antenna systems and applied in modern weather radars and satellite information systems.
Abstract in English:Abstract In this paper, a low profile substrate integrated waveguide (SIW) based self-quadplexing antenna with high isolation is demonstrated for multiband wireless applications. Here the SIW based resonator cavity is integrated with an “X”-shaped resonator and formed the four quarter mode cavities having the individual microstrip feed lines. Each quarter mode cavity consists of “V”-shaped slots of different lengths; are in front to feed line and produce the four distinct resonant frequencies at 7.8 GHz, 8.5 GHz, 10.2 GHz, and 10.6 GHz, respectively. The working principle depends upon the perturbation of higher-order modes in a particular quarter mode cavity. The minimum intrinsic isolation of below than −26dB is attained between any of the two input ports by adequately modifying the antenna dimensions. Hence, a single antenna consists of four individual signals without interfering with each other, which determines the self-quadplexing property of the antenna. The proposed antenna is realized for maximum efficiency and minimum value of frequency ratio. The measured gain of the proposed antenna is 4.5 dBi, 5.28 dBi, 7.1 dBi, and 7.4 dBi at the four resonant frequencies, respectively.
Abstract in English:Abstract A LiDAR architecture for autonomous cars is presented and validated by numerical and experimental results. The proposed scheme is based on indirect time-of-flight principle based on continuous-wave pseudorandom codes and incoherent detection for range evaluation. The range ambiguity and resolution are controlled by the parameters of the pseudorandom code. Experimental results are reported for target detection ranging from 13 to 1,000 m, as well as a demonstration of a dual-target detection, demonstrating the efficiency of the proposed LiDAR architecture to operate in real scenarios of autonomous cars. A measured range error of less than 0.6 % has been achieved for both single and dual-target detection.
Abstract in English:Abstract In this paper, a new optical fiber corrosion sensor based on metallic bilayers is described. The detection region is located at a fiber end facet and we present simulations as well as experimental results in controlled lab conditions for Ti(10 nm)/Al(10 nm) and Ni(5 nm)/Al(5 nm) bilayers. We perform the characterization of the device by numerical simulations using the COMSOL Multiphysics software, and with an analytical model, which makes use of the Fresnel equations. According to the simulations, the change in the reflected optical signal over time is related to variations in the thickness of the metallic films by the corrosive process and, consequently, the corrosion rate in each metal of the bilayer can be obtained. Upon the simulation results, sensor devices were fabricated by depositing thin metallic films on the cleaved facet of the optical fiber using the sputtering method. We show that the use of a metallic bilayer as a transducer, instead of a monolayer, improves the sensor measuring interval (20 ± 1 nm) and provides information about the corrosion rate along the corrosion process.
Abstract in English:Abstract This paper proposes the formulation of a sinusoidal basis function with a novel segmented edge condition to model the impulsive behavior of the surface electric current density at the edges of rectangular microstrip scatterers. In comparison to traditional basis functions, the one considered in this approach demands using very few modes to expand the induced current. The effectiveness of the proposed formulation is validated using the commercial electromagnetic simulator Ansys Designer. Good agreement between the results obtained with the proposed formulation and with the commercial software has been obtained.
Abstract in English:Abstract A low-cost spectrum analyzer is presented, based on a commercial software defined radio and an open-source application package. Fundamentals regarding the receiving operation and its sensitivity are presented, along with measurements, of two 8 and 12-bits software defined radio models. An application, run within GNU Radio, is presented, deployed to overcome the hardware analog-to-digital converter limitation to monitor wide bandwidths. Results are shown for two different frequency ranges, 200 MHz bandwidth.
Abstract in English:Abstract A new design of an ultra wide-band metamaterial absorber (MMA), with appreciable high absorptance insensitive to angle of incidence and polarization angle is presented in the manuscript. The MMA structure consists of three concentric rings with non-linear variation in the spacing and the thickness of the rings is controlled by a single parameter. The idea of utilizing nonlinear variation based unit cell resulted in high absorptance ultra wide-band frequency spectrum in X -band. The proposed MMA design is three layered structure. The metamaterial nature of the proposed device is explained by simulated values of Z eff( f ), μ eff( f ), ε eff( f ), and η eff( f ). The FWHM bandwidth of proposed MMA is 6.32 GHz (7.36 GHz-13.68 GHz). The fabricated MMA is ultra-thin with thickness of λo/15.3 at centre frequency 9.8 GHz. The experimental results show absorptance greater than 99% at 7.9 GHz and 11.7 GHz, covering entire X -band range makes this MMA appropriate for providing stealth technology for defense equipments by reducing radar cross section (RCS).
Abstract in English:Abstract This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioinspired computing and a general regression neural network (GRNN). This hybrid computational method, which utilizes the multi-objective cuckoo search algorithm combined to a GRNN, determine the best physical dimensions of the FSS in order to achieve a multi-band filtering at the 2.4, 3.5 and 5.8 GHz spectrums. Therefore, the results are to be applied to aid the propagation of Wi-Fi, WLAN, WiMAX and future sub-6 GHz 5G systems. The resonant frequencies were measured and a -10 dB cutoff value has been considered for the transmission coefficient. The triple rectangular loop conductor geometry of the device is printed upon a glass epoxy (FR-4) substrate. Measurements were made for different wave incidence angles, from 0° up to 45°, to demonstrate how signal incidence would affect the device’s functioning. The agreement between simulated and measured data display satisfactory results.
Abstract in English:Abstract This article presents the proposed structure and the simulation results from analytical and numerical modeling of two corrosion sensor elements in D-shaped optical fiber: one based on the lossy mode resonance (LMR) effect and the other based on the effect of surface plasmon resonance (SPR). In the first sensor element, a bilayer of titanium dioxide – aluminum (TiO2-Al) is deposited on the D-shaped region, operating in LMR conditions, while, in the second sensor element, an aluminum (Al) monolayer is deposited under D-shaped region, operating in SPR condition. The sensor elements can operate separately, enabling simultaneous two-parameter measurements at two different points, or they can operate in cascade configuration, increasing the operating range and sensitivity of the sensor set. The D-shaped region of the optical fiber is modeled with an analytical model based on the Fresnel formulation, and also with a numerical model, which uses the finite element method with the COMSOL Multiphysics 5.2 software. The transmission of light through the D-shaped region causes peculiar variations in each light polarization in each sensor element, depending on the metal thickness. Both regions are subject to a corrosive environment. The sensor elements are evaluated separately and in cascade configuration, using polarized and nonpolarized light. Finally, the obtained results show two resonance valleys for the same operating wavelength, resulting in a higher operating range with high sensitivity, compared to other corrosion sensor structures found in the literature.
Abstract in English:Abstract This paper presents a solution for sphere-shaped heterogeneities applied to the bioimpedance test. Such an approach has applicability for electrical impedance tomography, considering the impedance response for electrodes at the skin level, a healthy tissue composing a half-space, and a spherical anomaly representing a malignant or even benign tumor. The presented methodology consists of an inverse solution; however, it has high computational performance and can be later applied to an optimization procedure for generating medical images. The proposed formulation does not require a domain discretization and is validated in the paper using Finite Element Analysis.
Abstract in English:Abstract This article presents the development of an inclinometer device based on a Mach-Zehnder interferometer considering the effects caused by temperature variations. It was demonstrated the operation of a LPG-taper system for angle measurements. The practical results satisfactorily show reliable inclination measures, even with the cross sensibility effect caused by variable temperature.
Abstract in English:Abstract This work presents four systems for generation of optical subcarriers in the C-band in optical communications, based on serial and parallel amplified optical ring resonator with phase modulation and 10 GHz spectral spacing between subcarriers. The systems were numerically simulated and were able to generate between 83 to 145 subcarriers with output power levels of −5 to 26 dBm for an input power of 0 dBm and with flatness of 1.4 to 8 dB with a minimum OSNR of 30 dB.
Abstract in English:Abstract Nonlinear Transmission Lines (NLTLs) are a new technique for radio frequency (RF) generation. A loaded ferrite NLTL, known as a gyromagnetic line, uses a solenoid to provide an external magnetic bias. In space applications, specifically in satellites, the replacement of these solenoids by permanent magnets is desirable, eliminating the need for a DC current source, and reducing the weight and the effective cost of the launch. This work investigated and selected permanent magnets for this application, and then computationally modeled the magnet assembly to analyze the resulting magnetic field generated and obtained a uniform field region to meet the NLTL operating specifications. For this, we employed selection charts for the proper choice of material to use in an arrangement of magnets simulated by the electromagnetic software CST Microwave Studio . Magnetic fields with uniformity variations of less than 6% and 23% in regions extended over 18.5 cm and 58.8 cm, corresponding to line lengths of 26.6 cm and 68.0 cm, respectively, were achieved in simulations.
Abstract in English:Abstract For vehicle tactical radio communications, positioning antennas along the structure is a complex task. In vessels, there are several radio systems installed operating from HF to SHF. Consequently, the antennas need to share the same restricted space while preserving electromagnetic compatibility. In this context, this work presents a parametric analysis of the positioning of HF monopole antennas on the upper bridge of a typical Navy frigate. A numerical antenna analysis tool was chosen to support the intended analysis. Six positioning scenarios were simulated, evaluating the performance change of figures of merit such as the reflection coefficient and gain, due to the mutual coupling between the antennas and the main metallic objects within their close range. Furthermore, from the analysis, it was possible to establish recommended distances of decorrelation between the antenna and the main nearby objects.
Abstract in English:Abstract Compressors operating in refrigeration systems, typically with built-in induction motors, represent an important energy demand. The applicability of standard methods for efficiency determination of induction motors is limited in this context by the constructive characteristics of these motors, such as the shared compressor frame and the inaccessibility of the shaft. The main contributions of this paper are to provide an overview of standard and alternative methods for efficiency testing of single and polyphase motors, according to technical standards and to the state of the art, and to offer guidelines for the method selection. The options cover dynamometer tests, loss segregation and equivalent circuit methods, some even applicable without direct access to the motor. Experimental application examples in single and three- phase motors are presented. Beyond the context of compressors, the discussion is relevant for inaccessible motors in general.
Abstract in English:Abstract In this paper, we present a mode-matching-based formulation for the electromagnetic analysis of multifurcated waveguide problems, that is, the junction of a number of input waveguides with an output region of larger cross-section area. A generalized scattering matrix (GSM) representation is obtained for relating the forward and backward modal field amplitudes in each of the waveguides in terms of coupling integrals representing the conservation of the reaction of the electromagnetic fields. Numerical results for several multifurcated coaxial waveguide devices are provided to validate the formulation. Comparisons against the finite-element method demonstrate that the present approach can accurately model multifurcated waveguide problems. The method introduced here provides useful matrix formulas that allow us to model multi-port waveguide devices by reusing well-known coupling integrals of two-port problems.