Resumo em Inglês:

Abstract We proposed and analyzed a planar narrow-band absorber based on a bi-layer metal/dielectric structure. The planar absorber uses the Fabry-Pérot resonance and the inherent loss of the metals, for maximum light absorption in the range of the electromagnetic spectrum visible to the near infrared. The absorption resonance peak can be shifted to other regions of the spectrum by varying the dielectric film thicknesses. It is also possible to control the absorption with the angle of incidence for TE and TM polarization modes. The high absorption (near unity) and the high tolerance to fabrication errors of the proposed absorber can be explored in a large number of optoelectronic devices.

Resumo em Inglês:

Abstract The dynamic weather condition is a major concern for optimum channel utilization in recent times, especially at higher frequencies with larger bandwidth for 5G applications. Over the years, rain-induced attenuation among the hydrometeors has been linked as the major cause of signal impairment especially at the frequency, f ≥ 10 GHz. However, when f > 18 GHz, the significant impact of other hydrometeors; cloud/fog, and scintillation increases tremendously, especially for Low Earth Orbit, LEO satellites. LEO satellites find applications in fibre optics technology, scientific research, remote sensing, surveillance, meteorology, satellite imaging, and other applications. In this paper, the assessment of combined impairments based on 5-year (2012-2016) data has been carried out and a dynamic adaptive intelligent scheme (DAIS) has been adopted to achieve a good quality of service along the satellite channels operating at Ku-V band frequencies over five stations representing different climatic regions in Nigeria namely: Port Harcourt (PH), Akure, Ilorin, Zaria, and Kano. The proposed DAIS based on fuzzy logic was able to achieve a significant reduction in the transmitting power by about 70% and SNR by 50% across the frequencies considered without altering the information content of the downlink parameters, thereby improving the QoS significantly and adhere to Customer Service Level Agreements (CSLAs) irrespective of the weather dynamics. The overall results show that the adaptive intelligent techniques can effectively fix signal links under the dynamic weather conditions for both satellite and wireless networks in this region. Information from the results is timely because it will serve as the bedrock for the newly launched transformation to the digital video broadcasting (DVB) system in Nigeria for effective service delivery.

Resumo em Inglês:

Abstract The paper proposes a high gain, metamaterial based super wideband (SWB) antenna. The SWB antenna has two inverted U slots which are responsible for two notches at 3.5 GHz and 5.5 GHz frequencies. A flower-shaped slot is etched from the radiator to obtain the SWB characteristics. The super wideband antenna has dimensions of 30×35 ×1.5 mm3 with FR4 substrate. The antenna has a frequency bandwidth of 3.1 GHz - 15 GHz for S11 < -10dB. A metamaterial unit cell is designed and simulated for permittivity and permeability characteristics. This shows a negative refractive index in the band of 2.4 GHz to 8 GHz and 8.2 GHz to 9 GHz. A 3×3 array of metamaterial cells is used as a superstrate for the improvement of the gain characteristics. The fabricated prototype SWB antenna with superstrate has measured frequency bandwidth 3.1-15 GHz with notched bands at 3.5 GHz and 5.5 GHz. The experimental and simulated results are in line with each other.

Resumo em Inglês:

Abstract The design and characterization of single and multi-layered miniaturized microstrip antennas resonating at 2.4 GHz are proposed. The miniaturization is accomplished by fractal Defected Ground Structure (DGS). The DGS used for miniaturization is a Modified Minkowski Fractal DGS (M-MFDGS). The proposed size reduction process with M-MFDGS follows the selection of the best antenna configuration and its design parameters through sensitivity analysis and pattern search optimization. Microstrip patch antennas with three different feeding mechanisms are considered here to validate the effect of DGS over the size reduction and performance improvement. Incorporating M-MFDGS in three antennas, the first one with microstrip line feed accomplishes a maximum patch area reduction of 70% among the three proposed structures with a gain of 1.43 dBi. Likewise, with a slightly higher dimension than the first structure, the second antenna with proximity-coupled feed achieves a higher gain (5.11 dBi) and bandwidth (110 MHz). Although the size reduction in the third antenna with aperture-coupled feed is a little less it has the highest gain (5.91 dBi) among all the three. All three compact antennas are physically fabricated and the simulated results are validated with the measured results.

Resumo em Inglês:

Abstract In this paper, a millimeter-wave printed quadrupole antenna is proposed. It consists of two symmetric printed dipoles that make the quadrupole radiating power omnidirectionally. Such an arrangement eliminates the influence of the ground as reflector. Simulation results show that the quadrupole antenna exhibits a broad impedance bandwidth and an enhanced gain compared to conventional dipoles. More interestingly, the configuration of the quadrupole includes an integrated feed network, making the design compact. Next, a novel omnidirectional array was designed, simulated, fabricated, and measured, exhibiting enhanced features like compactness, broad bandwidth, high gain, high efficiency, low cross-polarization, low cross-polarization level, low cost, and low profile.

Resumo em Inglês:

Abstract The Amazon region has high lightning occurrence rates, with many lightning hot spots. Different rivers cross the Amazon rainforests and the people that live there use these rivers as roads to go from one place to another. Every year, lightning deaths are reported in the Brazilian Amazon region. In 2018, a lightning discharge struck a small riverboat, which killed 4 people and injured 5 in the North region of Brazil. In this study, we investigate lightning fatalities in Amazon rivers and compute electric field distribution in a small riverboat due to a lightning strike using the finite-difference time-domain (FDTD) method. The results show that the electric field produced inside the boat is large enough to cause air breakdown. Additionally, we propose a cost-effective method to improve lightning safety for people that use small boats in the Amazon region.

Resumo em Inglês:

Abstract In this paper, a compact, planar printed microstrip line fed pentagonal shape ultra-wideband antenna with triple band-notched characteristics is proposed and investigated. By incorporating a pair of mirrored Γ-shape, a pair of mirrored L-shape slots in the pentagonal patch and bent C-shape parasitic strip at the backside of a patch, the tunable band notched responses are realized. The proposed antenna is fabricated on Rogers RO3003 substrate with permittivity 3.0 and thickness of 0.76 mm. The measured results indicate that the proposed antenna having dimensions of 32 × 24 × 0.76 mm3 has a bandwidth over the frequency band 2.7-10.6 GHz with S11 ≤ -10 dB (VSWR ≤ 2), except in WiMAX band (3.27-3.85 GHz), WLAN band (5.6-5.95 GHz) and ITU-T band (7.84-8.46 GHz). The presented antennas show dipole- like patterns in E-plane and omnidirectional in H-plane, minor group delay variation, and nearly constant gain at operating frequencies.

Resumo em Inglês:

Abstract Fault current limiters are essential devices used to protect the power system and its equipment against high levels of fault current, which are growing up due to the increase of new power sources. This paper proposes a novel design of a Hybrid Superconducting Fault Current Limiter (Hybrid SFCL), which is composed basically by thyristors in series with a superconducting element. This branch is connected in parallel to an air-core reactor, which improves limitation and ensures the safe operation of the superconductor element. Another advantage of this topology is the use of the voltage drop in the superconductor as an input parameter to the controller. This voltage is used to detect the fault, which avoids the need for a current sensor and, consequently, reduces the manufacturing costs. In this work, the PSCAD/EMTDC software was employed to modeling the Hybrid SFCL and the 2G superconducting tape, which was modeled considering the thermal-electrical analysis. The results show that the fault current is efficiently limited, and the developed controller strategy has shown a relatively good performance. Furthermore, the proposed system guarantees a fast recovery time, in the order of 500 ms, which is a good advantage when compared to the conventional resistive SFCL.

Resumo em Inglês:

Abstract A multiband magneto-dielectric resonator antenna with cylindrical geometry is proposed in this paper. The resonator is composed of yttrium iron garnet (YIG) with chemical composition Y3Fe2(FeO4)3. The final structure is built on a low-cost FR4 dielectric substrate. With only one resonator, the antenna is able to resonate in three distinct controlled frequency bands. These are the three propagation modes HEM11δ, TE01δ, and TM01δ, which are possible to be independently controlled at each input port of the resonator antenna. The resonator’s port was suitable designed to feed specific modes of the antenna using microstrip lines placed judiciously to excite each mode. Analytic, numerical, and experimental studies were performed and, after optimization, the final antenna design was obtained. The obtained simulated and measured S-parameters results are below -10 dB at the resonance frequencies 5.75 GHz, 6.86 GHz, and 8.37 GHz. The corresponding measured bandwidths are 370 MHz, 120 MHz, and 1060 MHz, respectively. The antenna has a total size of 32.5 × 32.5 × 8.35 mm3. Measured radiation patterns and gain are also presented and show good agreement when compared to simulated results.

Resumo em Inglês:

Abstract Irregular terrains covered with forest vegetation represent a challenging scenario for radio planning. A case of particular interest is the one where a forest-covered high hill or mountain is interposed to the link, for which typical diffraction loss models usually apply as good approximations, even disregarding the vegetation influence. Pragmatic approaches to incorporate the forest contribution, such as adding a clutter height, usually improve accuracy a little further. In this scope, this paper assesses the performance of some models based on the Uniform Theory of Diffraction (UTD) for RF path loss prediction in such ridges. Special attention goes to a hybrid model in which the forest is a uniform layer over a wedge that represents the ridge, and its influence is incorporated into the diffraction coefficient. The path loss predictions are compared with measurements from a mountainous region of the USA, and the statistical adherence of the models to the measured data is discussed. Overall, the slightly better performance of the models which incorporate the vegetation influence was confirmed, the hybrid model performing the best for frequencies below 910 MHz.

Resumo em Inglês:

Abstract Superconducting Fault Current Limiter (SFCL) modules with distinct arrangements have been investigated, seeking design and performance enhancements. In this context, this work aims to propose a design for resistive SFCL (R-SFCL) modules, using RE-Ba-Cu-O high-temperature superconducting tapes (HTS) wound on an alternative support material. An R-SFCL bench prototype was designed for 400 A and 500 V. Two pieces of 2G tapes, arranged in a bifilar antiparallel configuration were wound on Acrylonitrile Butadiene Styrene (ABS) tubes, which were made by means of a 3D printer. During the experiments, the SFCL was immersed in an open bath cryostat with liquid nitrogen and several measurements were carried out. The average limited current is about three times lower than the prospective one. To test the SFCL recovery time, the following procedure was adopted: The fault is induced during three cycles, and after, the current is reduced to zero. The SFCL is reconnected after some time considering that the fault was extinct, and the voltage level returned to normal operation. The results showed promising levels of limitation and recovery time for further developments.

Resumo em Inglês:

Abstract Several formulae for computing the direct coupling efficiencies from laser diodes to diffused channel waveguides, based on mathematic models for approximating the corresponding laser beams and the waveguiding modes, have been derived in this paper. Then, the authors utilize a simple shift-or-shrink (SOS) algorithm to seek their optimal coupling conditions, including the incident positions of the laser beams and the corresponding horizontal and vertical beam widths. The simulation results are presented and compared.

Resumo em Inglês:

Abstract Fiber optic access networks have been considered a definitive solution to the constant need for increasingly higher bandwidths. For this reason, PON (Passive Optical Network) have grown enormously in the recent years, offering different solutions to the end customer, whether it is residential or business. However, the PON project is complex and a time-consuming process. This paper is focused on a tool design that, when combined with the schematic of the PON project, performs the survey of all equipment used in the projected cell. This tool provides also the attenuation calculations, as well as the techno-economic study of the network. Simulations were carried out to test the viability of the software, considering the network analysis in two cases: with one service provider using the network or with two service providers sharing it.

Resumo em Inglês:

Abstract Monopulse radars operate with simultaneous beams and are used for tracking purposes, relying only on hardware to provide a real-time indication of the target position. A monopulse array and its feeding network is implemented and tested, in the frequency of 5.4 GHz, based on patch antennas using dieletric to provide wide bandwidth and high gain. The system field styrofoam as pattern was evaluated in two different environments, a shielded room and an indoor area. Results agreed with simulation for either individual elements as well as the final integrated monopulse array.

Resumo em Inglês:

Abstract The meshless element-free Galerkin method (EFGM) is used to solve partial differential equations responsible for obtaining the electromagnetic fields generated by a transmission line. For this purpose, a 2D model based in a real transmission line is constructed and simulated. The results obtained by EFGM have good accuracy and they are compared against analytical solution and Finite Element Method in order to verify the effectiveness, advantages and disadvantages of the method.

Resumo em Inglês:

Abstract In this paper, we propose a simple technique to analyze absorber/transmitter frequency selective surfaces (FSS). The structure is formed by two FSS, one resistive and one conductive. Both FSS are printed on an FR4 dielectric substrate. The square loop and crossed dipole are the geometries considered in this paper. The technique combines two simple approaches, the equivalent circuit method, and the scattering matrix method. Two prototypes were built for validation purposes. Simulated and measured results are in good agreement.