Mario F. Pantoja

FDTD Modeling of Graphene Devices Using Complex Conjugate Dispersion Material Model

Graphene-based devices constitute a pioneering field of research for their extraordinary electromagnetic properties. The incorporation of appropriate models into numerical simulators is necessary in order to take advantage of these properties. In this work, we propose a method to incorporate graphene-sheet models into the FDTD method. The use of vector-fitting techniques expands the permittivity of graphene into a rational function series of complex conjugate pole-residue pairs, which is implemented into FDTD by an auxiliary differential equation formulation. Simple waveguiding problems validate our approach.

GA design of a thin-wire bow-tie antenna for GPR applications

A microgenetic algorithm has been applied to design a new ultrawideband thin-wire bow-tie antenna for ground-penetrating radar applications. The broadband performance of the antenna is achieved by resistive loading and by optimizing the number of wires and the angular distances between those wires. The radiation characteristics of the optimized antenna are discussed, and its performance is compared to that of a resistively loaded Wu-King dipole.

Benchmark Antenna Problems for Evolutionary Optimization Algorithms

A set of antenna-optimization problems is presented that satisfies the necessary requirements to form a test suite useful for measuring and comparing the performance of different evolutionary optimization algorithms (EAs) when they are applied to solve complex electromagnetic problems. The ability of the proposed test suite to find strong and weak points of any EA is illustrated by a complete study of four broadly used evolutionary algorithms carried out with the aid of the new test functions

A Hybrid Genetic-Algorithm Space-Mapping Tool for the Optimization of Antennas

A hybrid global-local optimization technique for the design of antennas is presented. It consists of the subsequent application of a genetic algorithm (GA) that employs coarse models in the simulations and a space mapping (SM) that refines the solution found in the previous stage. The technique is particularly suited to optimization problems for which long computational times are required to achieve accurate solutions

Microstrip-patch array design using a multiobjective GA

A Pareto multiobjective genetic algorithm (MOGA) has been applied to optimize the radiation characteristics of a 4/spl times/4 array of parasitically loaded microstrip-patch antennas in terms of sidelobe level (SLL), main-lobe half-power beamwidth, and dynamic range (DR). The geometry of the array configuration is fixed and the genetic algorithm (GA) finds the complex feeding coefficients of each element in the array.

HIRF Virtual Testing on the C-295 Aircraft: On the Application of a Pass/Fail Criterion and the FSV Method

In this paper, we show the application of numerical simulation for the virtual testing of a very complex system under high-intensity radiated fields (HIRF) conditions. Numerical results have been compared to measurements performed on a C-295 aircraft. The approach is based on the use of multiple tools for the preprocessing, computation, and postprocessing, all of them integrated under the same framework. This study is a part of the HIRF SE project, and the final step for the validation of the tools involved there, to introduce the use of simulation in the whole aircraft certification process in an HIRF environment. The main goal of the project is to provide the aeronautic industry with a numerical modeling computing framework, which could be used to predict the electromagnetic performance, and to carry out parametrical studies during the design phase, when changes are simpler and less costly. It could also lead in the future to a considerable reduction on the certification/qualification testing phase on air vehicles, to cross validate the results obtained from measurement and simulation providing best confidence in them, and to attain a more exhaustive analysis to achieve a higher level in the air vehicle safety.

A Comparison of the Performance of THz Photoconductive Antennas

This letter explores the influence of the geometry of bias electrodes in the performance of terahertz (THz) photoconductive antennas (PCAs). To this end, a methodology is presented to calculate numerically the operational bandwidth and radiation efficiency of the PCAs. The procedure is validated through a comparison to experimental measurements. Also, results are depicted from numerical simulations of different PCAs under varying conditions of bias voltage, doping factor, and incident optical power. It is concluded that an appropriate configuration of the electrodes may double the efficiency of the antennas, with a penalty in the bandwidth of the radiated pulse usually smaller than 10%.

Improving the SAR Distribution in Petri-Dish Cell Cultures

Petri dishes of different types are widely used in bioelectromagnetic experiments for the assessment of the non-thermal biological effects of electromagnetic radiation. Two important qualities required for the experimental setups are to guarantee a sufficiently high level of exposure and to maintain uniformity of the fields affecting the cell culture under study. In this paper, we apply two novel techniques to improve both parameters: the use of dishes with an elliptical shape and the addition of metallic patches underneath the Petri dish. Results for plane-wave illumination at 2.5 GHz are shown. This methodology can also be extended to Petri dishes inside waveguide applicators.

Time-Domain Numerical Modeling of THz Photoconductive Antennas

This paper presents a computational procedure to simulate the time-domain behavior of photoconductive antennas made of semiconductor and metal materials. Physical modeling of semiconductor devices at terahertz regime can be achieved by applying joint electronic and electromagnetic procedures, e.g., solving a coupled system of equations inferred from Poissons drift-diffusion and Maxwells equations. A set of discrete equations are derived by applying a combined finite-difference methodology for the previous steady-state and the finite-difference time-domain procedure for the transient regime. The results for the radiated electric field at broadside direction show good agreement with the experimental results previously reported in the literature.

TDIE Modeling of Carbon Nanotube Dipoles at Microwave and Terahertz Bands

In this letter, a novel procedure is introduced for the simulation of carbon nanotube (CN) antennas directly in the time domain. This formulation is based on the time-domain electric-field integral equation (TD-EFIE) for thin-wires, including external loads. Appropriate loads have been derived to match the physical response of single-walled CN media to external electromagnetic fields. The results show good agreement with a validated frequency-domain formulation. The time-domain formulation provides physical insight into the well-known characteristic effects of CN dipoles, such as slow-wave propagation and the existence of low-frequency resonances.