Resumo em Inglês:

Abstract Particle Swarm Optimization (PSO) algorithm has been applied in electromagnetics to design microwave absorbers. Generally, microwave absorbers are used for absorbing the electromagnetic radiation caused due to numerous electronic equipments and is being extensively used in stealth technology. The main aim of this paper is to find and analyze the minimized maximum reflection coefficient over a range of frequency and angle of incidence for a fixed number of layers and polarization. An improvised PSO algorithm has been suggested by utilizing a velocity restriction factor that intelligently searches for the optimum solution. The pareto principle with an improvisation in social and cognitive parameters has also been applied. The algorithm succeeded in finding better values of reflection coefficient for the microwave absorber structures comparatively. Based on the pareto principle a form of mutation technique is also used for better convergence. The results have been compared and tabulated for various combinations of the microwave absorber structure and the thickness of each layer is also optimized for a predefined database.

Resumo em Inglês:

Abstract In this paper, an optical coupler composed by a photonic quasi-crystal fiber (PQCF) with two cores is proposed. The structure is obtained by immersion of a quasi-periodic arrangement of air holes replicated twelve-fold in a conventional fiber optical constituted of pure silica. The cores are generated from defects caused due to absence of two air holes on each identical core and horizontally equidistant from the center of PQCF. The chromatic dispersion in each fiber core is ultra-flat around 38.12 ps.nm-1.km-1 and to verify the power transfer, the signal was launched on the left core and transferred to the right core in a propagation length of approximately 3.78 cm.

Resumo em Inglês:

Abstract The aim of this work is to propose all-optical logic gates based on surface plasmon polaritons (SPP's) coupling among spatially separated graphene sheets. This model consists of graphene nanoribbons embedded in silica (SiO2) substrate place in a distance such that allow an efficient coupling between the plasmonic modes of the waveguides. It was numerically analyzed the propagation's behavior of the SPP modes in an interferometric device as function of the chemical potential and geometrical parameters in order to obtain the AND/OR/XOR logic gates for OOK modulation.

Resumo em Inglês:

Abstract Analysis of the state of polarization of light guided by structures recorded in lithium niobate and lithium fluoride crystals indicates that the recording method is determinant in the formation of birefringent structures. Each structure was written with a single and continuous translation of the crystal transversally to the laser beam. Birefringence was observed in the structures recorded in both crystals, despite the lack of intrinsic birefringence in lithium fluoride. The recorded structures are anisotropic showing regions with different birefringence. The structure generated with femtosecond laser is directly linked to the recording method and the crystalline lattice. This characteristic can be advantageous for application in photonic devices.

Resumo em Inglês:

Abstract In this paper, an in-depth study of the electrical and optical characteristics of Polymer Light Emitting Diodes ITO/PEDOT: PSS/DP-PPV derivatives/Al(Ca) is presented. Three polymer materials are considered; poly(2,3-diphenyl-5-(4-heptyloxy-4'-oxytrimethylenediphenyl)-phenylenevinylene) (P1), poly(2,3-diphenyl-5-[4-(4-pentylcyclohexyl)phenoxy]-propyl-p-phenylene vinylene) (P2) and poly(2,3-diphenyl-5-(2-(1, 4, 5-triphenyl-1H-2-imidazoloyl)-1-oxytrimethylene phenyl) phenylene vinylene) (P3). The J-V characteristics are investigated using a device model which includes the injection, transport, and recombination mechanisms. The electron and hole mobility of each material are fitted to experimental data. The charge balance factor CBF, the external quantum efficiency EQE, the Langevin recombination rates and the singlet exciton densities profiles are studied. The results are found to be in a good agreement with experimental data especially in the low current densities region, indicating that these PLEDs electrons mobility affects greatly the J-V characteristics compared with holes mobility, and that is because electrons band offset smaller than that of holes. The best performance is obtained with P1 device with a CBF value of almost unity and an EQE still low (4.7 %) but similar to other PPVs and MEH-PPVs based devices.

Resumo em Inglês:

Abstract This paper presents an antenna loaded with metamaterial to enhance its gain and directivity to improve the performance of a ground-penetrating radar system (GPR). We adjusted the parameters of the antenna to change its equivalent capacitance and inductance and applied an operating frequency of 0.5 GHz-1.2 GHz to create an ultra-wideband antenna. On the basis of this operating frequency, we also designed the corresponding negative permittivity and permeability materials to simulate a patch antenna and material in a 1 GHz frequency band. The high gain and directivity of the antenna loaded with single-negative material were verified by simulation. Compared to the original antenna, the maximum gain increased by 7 dB and its directivity was greatly improved.

Resumo em Inglês:

Abstract The systemic behavior of a Semiconductor Optical Amplifier model was optimized through extensive simulations, reaching reasonable approximation to experimental obtained from commercial devices for the optical gain versus bias current, for different optical inputs powers (-25 up to 0 dBm), and for the gain saturation profile for different I-bias (0 up to 180 mA). For that, parameters such as active region thickness, confinement factor, linear gain coefficient, and the transparency current were adjusted by the presented method. The method can be applied for different SOAs, enabling more accurate numerical predictions for black-box devices.

Resumo em Inglês:

Abstract In this work, it is investigated an improved chaos particle swarm optimization (IC-PSO) scheme to refine the quality of the algorithm solutions regarding to solve the optimal power allocation in next generation passive optical networks (NG-PON)s. The proposed IC-PSO scheme utilizes the Beta distribution instead of uniform distribution of the traditional PSO. A factor of damping based in the chaotic logistic map related to the updating of the best global val ue is successful introduced. The numerical results corroborate the best relation between the performance-complexity tradeoff and the quality of the algorithm solutions for the proposed IC-PSO when compared with the classical PSO power allocation scheme.

Resumo em Inglês:

Abstract Vegetation is considered a complex environment for analysis of scattering and attenuation in radio propagation phenomena. Satellite image processing can improve planning of radio systems with a vegetation attenuation predictor. In this research, the prediction is based on the correlation of more than 56% between RGB pixel values and vegetation attenuation taken from three groups of power measurements at two distinct regions of Brazil: Belo Horizonte, in the southeast region measured at 18 GHz, and Manaus at 24 GHz in the north region. The statistical analysis showed that more than 30% of the attenuation variance was due to the pixel values for each group. Using this linear correlated model between vegetation pixel RGB values and geolocated attenuation values, this work combined the unscented transform (UT) and Bayesian inference to refine the vegetation attenuation distribution. Since the necessary multiplication of Bayes prior and sampling distributions is not easily available in the UT, this paper presents a method that calculates new common sigma points and different new weights for the prior and sampling UT distributions, thus allowing the multiplication and creating the basis for a machine learning predictor tool.

Resumo em Inglês:

Abstract This work shows the experimental validation of a method developed for determining the strain profile applied to a fiber Bragg grating by solving the inverse scattering problem. The non-uniform strain profile is recovered by formulating an optimization problem, solved with an algorithm based on differential evolution. The method has proved to be able of recovering the shape and approximate amplitude of the actual strain profile applied to the FBG, opening new perspectives for optical sensing with fiber Bragg gratings.

Resumo em Inglês:

Abstract This case study describes a new method using a fiber optic Bragg grating sensor to determine muscle fatigue in a patient wearing a resilient occlusal device for the treatment of bruxism symptoms. Four tasks performed at maximum bite force induced rapid exhaustion for the analysis of fatigue. The results show that it is possible to obtain a better understanding of the muscle fatigue process by using the fiber sensor. Differences between the bite patterns are detected at each phase of the induced fatigue. It is possible to compare the bite peak sensitivity coefficients for the exhaustion phase, 1.37 Ns-1, and for fatigue phase, 2.54 Ns-1. Additionally, the increase in the facial thermal profile is correlated to the different bite force pattern performed.