Leonardo L. Bravo-Roger

Spatio-temporal finite-element propagator for ultrashort optical pulses

An efficient finite-element formulation for the simulation of ultrashort optical pulses is thoroughly presented. This numerical propagator, capable to take into account spatial and temporal effects, incorporates a wide-angle-band Pade/spl acute/ approach and perfectly matched layers at the truncated boundaries. Its effectiveness and higher performance over other similar approaches are clearly demonstrated through key simulations.

Estudo do amortecimento do pêndulo simples: uma proposta para aplicação em laboratório de ensino

The pendula are largely used in teaching activities of physical introductory courses. Often, in these activities an ideal model is used to study the behavior of the pendulum. In this work a model that takes into account the oscillation damping is suggested. An experimental methodology is purposed aiming to detect the falling down of oscillation amplitude and to fit these data to a mathematical model. The results show that the simple pendulum, set up by a small volume sphere and oscillating on low speed, can be studied with simplified models. The methodology and the mathematical model are appropriated for the knowledge level of the students from physic introductory courses and offer a more realistic insight about the pendulum behavior.

The study of piezoelectric devices with Thévenin's Theorem

This work presents a study of the behavior of piezoelectric devices based on a modified Thévenins equivalent electric circuit. It aims to characterize piezoelectric devices using electric network theory and to complement the instruction of Thévenins Theorem in classes about electric circuits. The employed approach allows us to outline the most important concepts of operation of the piezoelectric transducers. The manner for obtaining the equivalent electric circuit and a simple experimental procedure are presented. The work shows that Thévenins Theorem, commonly taught in electric circuits classes, can be used for evaluating of piezoelectric devices. The methodology employed in this work facilitates the comprehension of the physical principles of the piezoelectric elements.

Experimental evaluation of the performance of a wireless sensor network in agricultural environments

Um estudo experimental, visando a avaliar a distância de operacao adequada entre os nos de uma rede de sensores sem fio disponivel no mercado, foi realizado para diferentes cultivos agricolas (milho, pinhao-paraguaio e eucalipto), buscando oferecer aos agricultores e pesquisadores dados experimentais do desempenho da rede, que possa good yield are environmental factors, which include high temperatures and high humidity within the facilities, causing stress to the animal and consequent decreased production (SOUSA, 2005).am ser uteis para ser considerados no dimensionamento e no projeto de redes de sensores sem fio em situacoes semelhantes as estudadas. A avaliacao mostrou que a distância de separacao dos nos depende do tipo de cultura e e um fator critico para garantir a viabilidade do uso da RSSF. Na configuracao usada, com envio de pacotes a cada 2 segundos, a autonomia da bateria foi de cerca de quatro dias. Portanto, a autonomia pode ser aumentada com um intervalo maior de tempo entre o envio de pacotes.

Comparison between narrow-angle-band and wide-angle-band spatio-temporal FEM and FD BPM codes for the propagation of ultrashort optical pulses

An efficient finite-element formulation for the simulation of ultrashort optical pulses is thoroughly presented. This numerical propagator, capable to take into account spatial and temporal effects, incorporates a wide-angle-band Pade approach and perfectly matched layers (PML) at the truncated boundaries. Its effectiveness and higher performance over other similar approaches are clearly demonstrated through key simulations.

Dielectric properties characterization: A simple inverse problem approach

A non-resonating technique for characterizing isotropic complex permittivity of dielectric substrates is presented. The technique is applicable to high or low ϵr and tan δ values. After measuring the S21 of a microstrip line with the unknown substrate, an inverse problem is built with an EM solver. Then, the complex permittivity parameters are extracted by means of solving the inverse problem using the Differential Evolution algorithm. The validity of the technique is assessed by characterizing two known and reliable dielectrics, in which the maximum error for the ϵr and tan δ was 7.6% and 16.67%, respectively.

Characterization and validation of a textile substrate for RF applications

The possibility of using “Santista denim” textile as a dielectric material in radio frequency (RF) and microwaves devices has been demonstrated by means of the design, implementation and characterization of a classical antenna. A commercial conductive textile was used as metallic parts of the antenna and the cited textile as substrate one. The characterization of textile and some theoretical and measured antenna parameters are shown in this manuscript.

Exploring dual-band RFID tag antennas by means of asymmetric dipoles

Some dual-band RFID (radio frequency identification) tag antennas were obtained from symmetric dipole type configurations by exploiting the harmonic frequencies. Based on this situation, new antenna configurations, easy to adjust, were proposed by breaking the symmetry of the original dipole antenna. Following this approach, we found novels dual-band RFID antenna operating at UHF and Microwaves.