Carlos Leonidas da S. S. Sobrinho

UPML FORMULATION FOR TRUNCATING CONDUCTIVE MEDIA IN CURVILINEAR COORDINATES

This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case is shown and the complete equation set is provided.

Analysis of antennas by FDTD method using parallel processing with MPI

As far as we are concerned, the implementation of the Finite Differences in the Time Domain (FDTD) method requires, for the solutions of several practical problems in electromagnetism, a long process time and a large amount of memory, what makes it impracticable in various cases, principally when the serial process is used. The current work deals with the concept of a Beowulf cluster and it aims to implement the FDTD method using parallel process for the study of antennas. The obtained system efficiency is then tested in the analysis of two antennas, i. e., a horn antenna and a monopole antenna, what is done by comparing the time spent in the parallel and serial processing.

Novel technique for locating an intruder in 3D environments by using a cooperative system of multistatic radars

the aim of this work is to present a new methodology, based on vector and geometrical techniques, for determining the position of an intruder in a residence (3D problem). Initially, modifications in the electromagnetic responses of the environment, caused by movements of the trespasser, are detected. It is worth mentioning that slight movements are detected by high frequency components of the used pulse. The differences between the signals (before and after any movement) are used to define a sphere and ellipsoids, which are used for estimating the position of the invader. In this work, multiple radars are used in a cooperative manner. The multiple estimates obtained are used to determine a mean position and its standard deviation, introducing the concept of sphere of estimates. The electromagnetic simulations were performed by using the FDTD method. Results were obtained for single and double floor residences.

Particle Swarm Optimization Applied for Locating an Intruder by an Ultra-Wideband Radar Network

As it was shown by the authors in a previous work, the Finite-Difference Time-Domain (FDTD) method is adequate to solve numerically Maxwells Equations for simulating the propagation of Ultra-Wideband (UWB) pulses in complex environments. These pulses are important in practice in high-resolution radar and GPS systems and in high performance (wideband) wireless communication links, because they are immune to selective frequency fading related to complex environments, such as residences, offices, laboratories among others. In this case, it is necessary to use spread spectrum techniques for transmission, in order to avoid interferences to other wireless systems, such as cell phone networks, GPS, Bluetooth and IEEE802.11. It is worth to mention that by combining these techniques to UWB pulses; it is possible to obtain a signal with power spectrum density under noise threshold, what is a very interesting characteristic for this application. The proposed simulated environment is a building consisting of several rooms (laboratories) separated by masonry. Internal and external walls are characterized by specific widths and electrical parameters. Wood doors were included in the analysis domain. The analysis region is then limited by U-PML (Uniaxial Perfectly Matched Layers) technique and the system is excited by omni-directional antennas. In order to make the simulations more real, Additive White Gaussian Noise was considered. Aiming at verifying the robustness of the radar network, objects are included in the domain in a semi-random spatial distribution, increasing the contribution of the wave scattering phenomena. Omni-directional antennas were used to register transient electric field in specific points of the scenery, which are adequate for the propose of this work. From those transient responses, it is possible to determine the time intervals the electromagnetic signal requires to travel through the paths transceiver-intruder-transceiver and transceiver-intruder-receivers, forming, this way, a non-linear system of equations (involving circle and ellipses equations, respectively). In order to estimate the intruder position, the PSO method is used and a new methodology was conceived. The main idea is to apply PSO to determine the equidistant point to the circle and to the two ellipses generated by using the data extracted from received transient signals (those three curves usually does not have a single interception point for highly

Use of square parasite elements to increase the bandwidth of planar monopole antenna for UWB systems

This work presents planar monopole antennas for UWB systems operating in the range 3.1-10.6 GHz. Initially an antenna with a width of 12 mm and a height of 20 mm was analyzed. The return loss characteristic and radiation pattern of this antenna was calculated by the FDTD method. Then, some techniques are presented with the purpose of to increase the antennas bandwidth, such as using square parasite elements around the main radiator.

Parallel-FDTD and experimental results of SAR for flat and head phantoms @ 900 MHz

In this work, computational simulations were performed in order to characterize the way electromagnetic radiation interacts with the human head. Average of realistic parameters of bio-materials, such as bones and head liquids, as well as near field radiation parameters of a half-wave dipole are beeing considered in order to achieve results. This way, a software was developed in which Maxwells equations are numerically solved by using a Beowulf cluster. The solver is based on the finite-difference time-domain method, associated to domain truncation by the uniaxial perfectly mactched layers technique and full-wave solutions have been obtained from the simulation. All averaged SAR values and electric field distributions inside modeled analysed structures have been compared to experimental results obtained in a full setup laboratory with all equipments necessary to perform dosimetric validations of telecomunication devices as shown in IEEE 1528.

Three-dimensional simulations of an urban outdoor wireless channel by the block-FDTD method

Full three-dimensional simulations of electromagnetic wave propagation in outdoor environments with the FDTD method the giga-hertz frequencies (or even mega-hertz) are not viable with the ordinary computational resources available nowadays. In order to reduce the required computational resources, especially memory, and make such simulations possible to perform in an eight-nodes-Beowulf-cluster, an alternative implementation technique is proposed: block-FDTD method, called here B-FDTD. The paper contains details about the method and results obtained by software developed based on B-FDTD, showing effects caused by ground and by diffractions generated at the edges of the buildings that compose the outdoor environment (time and frequency domains). The analyzed environment is 30/spl times/30/spl times/8 meters and received fields are registered at different points.

Electromagnetic scattering analysis in indoor and outdoor environments by applying FDTD method

Economical and efficient means to obtain the characterization of radio channels have been investigated a lot since mobile communication devices became popular. So, this article presents solutions and results for two electromagnetic scattering problems: an outdoor environment simulation, solved by applying the two-dimensional FDTD formulation and an indoor environment radiation scattering simulation, whose solution was based on the three-dimensional FDTD formulation. In both cases, the numerical domains were truncated by using the UPML formulation and solved though code parallelization techniques. Power received at specific points and field distribution are analyzed.

FDTD method: analysis of an one-dimensional array of H-plane sectoral horn antennas with dielectric lens

The FDTD method is used in the analysis of the radiation characteristics of a one-dimensional array antenna. Here, the array elements are two-dimensional H-plane sectoral horns with parabolic dielectric lenses. In this case, the dielectric materials used were chosen so that they have low dielectric constant in order to avoid considerable reflections on the air-dielectric interfaces. The numerical results obtained show that the distance between the array elements, and the lens characteristics, in spite of its low dielectric constant, change the phase distribution and power at the aperture of the array. For a suitable choice of these parameters, radiation patterns are obtained with low level of sidelobes.

DISPERSION CHARACTERISTICS OF ASYMMETRIC COUPLED ANISOTROPIC DIELECTRIC WAVEGUIDES USING FDFD

The formulation is developed in the frequency domain and the finite difference method is used for the numerical solution of the scalar wave equation, written in terms of the transverse components of the magnetic field. As a result a conventional eigenvalue problem is obtained without the presence of spurious modes due to the implicit inclusion of the divergence of the magnetic field equal to zero. The formulation is developed to include biaxial anisotropic dielectrics with an index profile varying arbitrarily in the cross section of the waveguide under analysis. This formulation is then applied to the analysis of the influence on the dispersion characteristics of the dimensions of asymmetric coupled rectangular uniaxial anisotropic dielectric waveguides. As expected, the reduction of the height or the width of one of the rectangular dielectric waveguides causes the dispersion curves to move towards higher frequencies.