Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 19 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Transverse Load Discrimination in Long-Period Fiber Grating via Artificial Neural Network]]> Abstract We present a general investigation of a Long-Period Grating (LPG) for transverse strain measurement. The transverse strain sensing characteristics, for instance, the load intensity and azimuthal angle, are analyzed with the data set generated by the LPG sensor and probed by artificial neural network (ANN). Furthermore, we evaluate and compare the predictive performance of the interrogation model considering the square correlation coefficient (R2), root mean square error (RMSE) and mean absolute percentage error (MAPE). The results indicate that the ANN model could be successfully employed to estimate the load intensity and azimuthal angle using a single LPG sensor. <![CDATA[QoS and QoE Aware Routing Protocol for Flying Ad-Hoc Surveillance Networks Using Fuzzy Inference Systems]]> Abstract The Flying Ad-hoc Network (FANET) networks have often operated in regions that are difficult to reach and have no fixed infrastructure. The use of devices such as Unmanned Aerial Vehicles (UAV) enable aerial networks to be created that are extremely fast, although there are no specific routing protocols for this type of network that can make communication more efficient among these devices. For this reason, this paper sets out a specific routing protocol for FANET networks that is designed for the discovery of routes among UAV devices. Evidence of the benefits of this strategy has been obtained through simulation by the Network Simulator version 2. <![CDATA[Modified Ring Power Divider Using Stepped-Impedance Resonator]]> Abstract In this paper, the design of a modified ring power divider dedicated for wideband communication or measurement systems is presented. The proposed power divider is built by using a conventional ring power divider and an additional Stepped-Impedance Resonator (SIR). The even-odd mode analysis is used to derive the design equations. In order to observe the bandwidth improvement, a comparative study between the designed device and the previously reported ring power divider is conducted. The electromagnetic (EM) simulated results show that the proposed divider has a fractional bandwidth of 90.2 % at the center frequency of 3.17 GHz. The measurement results of the fabricated prototype demonstrate high performance over the considered operational bandwidth from 1.7 GHz to 4.64 GHz with a return loss lower than −10 dB while maintaining a good insertion loss and a good isolation between the output ports. The maximum amplitude imbalance is better than 0.21 dB and the phase imbalance is better than 2.5 degrees between the output signals. The simulation and measurement results are in good agreement over the whole band of interest. <![CDATA[Inverse Design of Tapers by Bio-Inspired Algorithms]]> Abstract The efficiency of optical power transferred between two bidimensional waveguides, continuous waveguide and periodic subwavelength waveguide has been designed and optimized by using a taper composed by variable length segments (0.03 − 0.27 ┬Ám). Waveguides with variable width (270 − 330 nm) have been considered and the number of segments on the taper region has been varied from 10 to 15. The optimized taper was efficiently designed using bio-inspired algorithms based on the genetic algorithms and the artificial immune system. The power coupled has been computed using the frequency domain finite element method. The best solution is 20% shorter than previously existent tapers with coupling light efficiency above 90% over a broadband interval of frequencies and it exhibits high fabrication error tolerances. <![CDATA[Electromagnetic Energy Harvesting Using a Glass Window]]> Abstract In this work, a new constructive and conceptual model for rectenna, using glass as dielectric substrate, was proposed. This research aims to produce a window for building facades that can harvest the electromagnetic energy available in the environment. For this proposal, a slotted patch antenna was designed with two main objectives: to have a low value of S11 parameter and to allow the maximum visibility through the glass. In order to accomplish an efficient radio frequency to direct current conversion, a voltage doubler rectifier was designed and built in the same glass substrate, directly connected to the antenna. The final system is a window composed of eight individual rectennas associated in parallel. For improving the window energy harvesting ability, a metamaterial structure was added to each rectenna element, which acts in order increases the patch antenna gain. Each rectenna was designed by using both Advanced Design System and Computer Simulation Technology softwares and optimized to operate at 2.45 GHz. The measured results show that the proposed rectenna model is an efficient solution to improve the total amount of harvested energy, which is enough to power a low consumption load. <![CDATA[Analysis and Optimization of Ultra-Low-Power Rectifier with High Efficiency for Applications in Wireless Power Transmission and Energy Harvesting]]> Abstract The system capable of harvesting RF energy from the environment through an antenna and converting it into direct current energy to deliver to a load is known as rectenna. The rectifier circuit is an important part of the rectenna and its modeling is arduous since it employs a non-linear device working at extremely low power levels. In addition, there are some losses in the system. Thus, the design of a high-efficient rectifier is a great challenge. In this work, several rectifier topologies are optimized, using the Genetic Algorithm, in order to achieve the highest efficiency and output voltage. An analysis of the influence of the variables on the output of these rectifiers was also performed. The topologies under investigation were optimized for −15 dBm input power and 2.45 GHz operating frequency, in accordance with the most suitable band for energy harvesting. Under these conditions, the Monodiode Series topology presents the best performance. When the input power is −15 dBm, it presents an output voltage of 402 mV and an efficiency of 51.3%. At that power level, the achieved efficiency is higher than that found in the literature. <![CDATA[Characterization of the Dielectric Properties of the Tommy Atkins Mango]]> Abstract This paper presents the characterization of dielectric properties (dielectric permittivity and dielectric loss factor) of Tommy Atkins mango (Mangifera indica L), a fruit produced in several regions of Brazil, of great economic importance. The fruits were characterized according to their maturation index, by probe method, and identified by the yellowish tone in their bark. The results allowed correlating the dielectric characteristics of the fruit with the physicochemical transformations that occurred in the maturation process of the mango Tommy. It was also verified a greater variation in the frequencies below 1 GHz, with the maturation indicated by the dielectric signature on the fifth day after the harvest. From these results, we can observe the use of electromagnetic materials and techniques in the solution and optimization of processes in agriculture can improve the quality of products consumed or suggesting best practices to the productive sector. <![CDATA[3.4/4.0 GHz Tunable Resonant Cavity in SIW Technology Using Metal Post and PIN Diode on a Low-Cost Biasing Network for 5G Applications]]> Abstract This paper presents a dual-band resonant cavity in Substrate Integrated Waveguide (SIW) technology to operate in the range from 3.3 GHz to 4.2 GHz, spectrum considered for the Fifth Generation (5G) network. The cavity was designed to operate at 3.4 GHz and 4.0 GHz. To achieve different states, a jumper and a PIN diode switch are considered as switching elements, connecting and disconnecting the bottom and the upper walls of the SIW resonant cavity through a metal post inserted inside its internal volume. A fitting equation is proposed to predict the maximum resonance frequency caused by the insertion of a single metal post inside the internal volume of the SIW resonant cavity and a new low-cost biasing network is designed on a thin dielectric substrate allocated on the upper wall of the SIW resonant cavity, using transmissions lines and a single capacitor, reducing the final cost and the insertion losses. Good agreement was observed among the fitting equation, computational electromagnetic simulations, and experimental results, validating the proposed methods. <![CDATA[Physics-Based Design of Microstrip Magnetic Dipoles Using Cavity Model]]> Abstract This paper presents an efficient technique of microstrip magnetic dipoles design that explores the physics ruling the antenna behavior not restricting to parametric analyses in a full-wave simulation software. The proposed approach makes use of the cavity model whose parameters are progressively enhanced by using full-wave electromagnetic simulation data in a feedback scheme. A curve fitting problem is established to evaluate the mentioned parameters at each iteration. To exemplify the developed technique, a microstrip magnetic dipole operating at 2.44 GHz (ISM band) was synthesized and its prototype was manufactured and tested in an anechoic chamber. The design was ready in less than one hour and only three full-wave simulations were required. A good agreement between theoretical predictions and experimental results was also observed. <![CDATA[Mutual Coupling Reduction in Phased Array Antennas Applying High-Impedance Surface at X Band]]> Abstract This paper presents a microstrip phased array using High Impedance Surface - Electromagnetic Bandgap (HIS-EBG) in order to minimize the effects of mutual coupling among the antenna elements. Each element of the array is fed by a coaxial cable allowing the beam steering by controlling the signal of the input port of each element. This phased array operates at X Band as well as the bandgap of the HIS-EBG structure. Its main applications are satellite communication and broadcasting systems. Results show reductions in the mutual coupling up to 12 dB, and improvements in the return loss and gain. <![CDATA[Sixteenth-Mode Substrate-Integrated-Waveguide (SMSIW) Resonator for Dielectric Characterization of Liquid Mixtures]]> Abstract In this work, a new concept of planar resonator technique for measurement of liquid mixture permittivity is proposed, designed, and implemented using a Sixteen-Mode Substrate Integrated Waveguide (SMSIW) technology. To design the proposed sensor, the conventional SMSIW resonator is designed with an additional air hole on the open side, and then we add a mask from the bottom side to close the air hole, which we fill with liquid under test (LUT). The detection principle is based on the resonance perturbation method. This perturbation yields a shift in resonant frequency due to the permittivity variation of the LUT inside the hole. The proposed sensor has been simulated using the commercial electromagnetic simulator: Ansoft HFSS. The SMSIW sensor has been tested for water, methanol, and ethanol as examples of liquids and water-ethanol with different concentrations as a liquid mixture. In order to validate the simulated results of the proposed concept, the sensor prototype is designed, fabricated and tested. The sensor is simple in design and low cost, which may be applied for various industrial applications.