Optimizations of Patch Antenna Arrays Using Genetic Algorithms Supported by the Multilevel Fast Multipole Algorithm

We present optimizations of patch antenna arrays using genetic algorithms and highly accurate full-wave solutions of the corresponding radiation problems with the multilevel fast multipole algorithm (MLFMA). Arrays of finite extent are analyzed by using MLFMA, which accounts for all mutual couplings between array elements efficiently and accurately. Using the superposition principle, the number of solutions required for the optimization of an array is reduced to the number of array elements, without resorting to any periodicity and similarity assumptions. Based on numerical experiments, genetic optimizations are improved by considering alternative mutation, crossover, and elitism mechanisms. We show that the developed optimization environment based on genetic algorithms and MLFMA provides efficient and effective optimizations of antenna excitations, which cannot be obtained with array-factor approaches, even for relatively simple arrays with identical elements

Novel electromagnetic surface integral equations for highly accurate computations of dielectric bodies with arbitrarily low contrasts

We present a novel stabilization procedure for accurate surface formulations of electromagnetic scattering problems involving three-dimensional dielectric objects with arbitrarily low contrasts. Conventional surface integral equations provide inaccurate results for the scattered fields when the contrast of the object is low, i.e., when the electromagnetic material parameters of the scatterer and the host medium are close to each other. We propose a stabilization procedure involving the extraction of nonradiating currents and rearrangement of the right-hand side of the equations using fictitious incident fields. Then, only the radiating currents are solved to calculate the scattered fields accurately. This technique can easily be applied to the existing implementations of conventional formulations, it requires negligible extra computational cost, and it is also appropriate for the solution of large problems with the multilevel fast multipole algorithm. We show that the stabilization leads to robust formulations that are valid even for the solutions of extremely low-contrast objects

Radyo Frekansı Tanımlama Uygulamaları İçin Inkjet Anten Optimizasyonları

TÜBİTAK EEEAG Proje15.09.20181002 programı kapsamında TÜBITAK tarafından desteklenen Radyo Frekansı TanımlamaUygulamaları Için Inkjet Anten Optimizasyonları baslıklı bu projede, son yıllarda artarakkullanılan radyo-frekanslarında tanımlama (RFID) sistemleri için özgu?n ve etkin antenlerintasarlanması amaçlanmıs. Özellikle ucuz inkjet baskı yöntemine uygun olarak tasarlananRFID antenlerinin benzetim ve tasarımları, proje kapsamında gelistirilen ve sonlu yapılarınanalizlerini saglayan bir integral denklemi yönteminin genetik algoritmalarla içiçe geçtigi yenibir optimizasyon mekanizmasıyla gerçeklestirilmistir. Elde edilen tasarımların u?retilmesi veRFID uygulamaları kapsamında test edilmesiyle, optimizasyon mekanizmasının etkinligikanıtlanmıstır. Optimizasyon mekanizması, sadece inkjet baskıya uygun RFID antenlerinindegil, aynı zamanda benzeri radyo-frekans ve mikrodalga bilesenlerinin de gerçekçi olaraktasarlanmasına olanak saglamaktadır.Radio-frequency identification (RFID) is a technology that is becoming increasingly popularparticularly for automated tracking applications in healthcare, defense, automotive, food, andsimilar service sectors. In general, a low-cost RFID system consists of a receiver/transmitterreader and passive cards (tags). This kind of an RFID system can be useful particularlywhen tags are inexpensive. Developments in recent years have greatly reduced the cost ofthe microchips. However, this is not sufficient, and the tag antennas should also beproduced via low-cost methods. In this direction, inkjet antennas, which can be produced byusing silver-based toners in standard printers, have been proposed and used in RFIDapplications. Low conductivity and sensitivity problems encountered in printing have beensolved via heating and curing, while issues in soldering to connect antennas to microchipshave been overcome by resorting to conductive epoxy. On the other hand, since the qualityof inkjet antennas heavily depends on many factors, such as printer parameters, silver ratiosin inks, paper types, heating temperature and duration, detailed parametric analyses arerequired. Despite these analyses, it is known that even two antennas that are producedsimultaneously may possess different characteristics (shifting in operating frequencies anddifferent power reflection dip values).In the literature, inkjet antennas have been studied for nearly 10 years. Nevertheless, theproblems encountered in these antennas described above have restricted their widespreadusage (despite their cost advantages). In this context, the narrowband nature of RFIDsystems has been misleading, as if the antennas can also be narrowband. Even in relativelysimple simulations, omitting dielectric effects and neglecting precise feed models have madethe designed antennas impractical in real life. In this direction, the novel aspects of thisproject have been developing and using a full-wave solver that can model both metallic anddielectric parts for precise analysis of inkjet antennas, combining the developed solver withheuristic algorithms for a robust optimization mechanism, and designing novel inkjetantennas using this mechanism, as well as testing them in RFID systems. The fabrication ofprototypes and their investigation in realistic RFID scenarios have demonstrated theeffectiveness of the optimization mechanism, in addition to the effectiveness of the designs.Keywords: Radio-frequency identification (RFID), inkjet antennas, computationalelectromagnetics, electromagnetic optimizations

Iterative Solutions of Hybrid Integral Equations for Coexisting Open and Closed Surfaces

We consider electromagnetics problems involving composite geometries with coexisting open and closed conductors. Hybrid integral equations are presented to improve the efficiency of the solutions, compared to the conventional electric-field integral equation. We investigate the convergence characteristics of iterative solutions of large composite problems with the multilevel fast multipole algorithm. Following a thorough study of how the convergence characteristics depends on the problem geometry, formulation, and iterative solvers, we provide concrete guidelines for efficient solutions

Preconditioned MLFMA Solution of Multiple Dielectric-Metallic Composite Objects with the Electric and Magnetic Current Combined-Field Integral Equation (JMCFIE)

We consider fast and accurate solutions of scattering problems involving multiple dielectric and composite dielectric-metallic structures with three-dimensional arbitrary shapes. Problems are formulated rigorously with the electric and magnetic current combined-field integral equation (JMCFIE), which produces well-conditioned matrix equations. Equivalent electric and magnetic surface currents are discretized by using the Rao-Wilton-Glisson (RWG) functions defined on planar triangles. Matrix equations obtained with JMCFIE are solved iteratively by employing a Krylov subspace algorithm, where the required matrix- vector multiplications are performed efficiently with the multilevel fast multipole algorithm (MLFMA). We also present a four-partition block-diagonal preconditioner (4PBDP), which provides efficient solutions of JMCFIE by reducing the number of iterations significantly. The resulting implementation based on JMCFIE, MLFMA, and 4PBDP is tested on large electromagnetics problems

Efficient solution of the electric and magnetic current combined-field integral equation with the multilevel fast multipole algorithm and block-diagonal preconditioning

We consider the efficient solution of electromagnetics problems involving dielectric and composite dielectric-metallic structures, formulated with the electric and magnetic current combined-field integral equation (JMCFIE). Dense matrix equations obtained from the discretization of JMCFIE with Rao-Wilton-Glisson functions are solved iteratively, where the matrix-vector multiplications are performed efficiently with the multilevel fast multipole algorithm. JMCFIE usually provides well conditioned matrix equations that are easy to solve iteratively. However, iteration counts and the efficiency of solutions depend on the contrast, i.e., the relative variation of electromagnetic parameters across dielectric interfaces. Owing to the numerical imbalance of off-diagonal matrix partitions, solutions of JMCFIE become difficult with increasing contrast. We present a four-partition block-diagonal preconditioner (4PBDP), which provides efficient solutions of JMCFIE by reducing the number of iterations significantly. 4PBDP is useful, especially when the contrast increases, and the standard block-diagonal preconditioner fails to provide a rapid convergence

Hierarchical Parallelization of the Multilevel Fast Multipole Algorithm (MLFMA)

Due to its O(NlogN) complexity, the multilevel fast multipole algorithm (MLFMA) is one of the most prized algorithms of computational electromagnetics and certain other disciplines. Various implementations of this algorithm have been used for rigorous solutions of large-scale scattering, radiation, and miscellaneous other electromagnetics problems involving 3-D objects with arbitrary geometries. Parallelization of MLFMA is crucial for solving real-life problems discretized with hundreds of millions of unknowns. This paper presents the hierarchical partitioning strategy, which provides a very efficient parallelization of MLFMA on distributed-memory architectures. We discuss the advantages of the hierarchical strategy over previous approaches and demonstrate the improved efficiency on scattering problems discretized with millions of unknowns

Accurate and efficient solutions of electromagnetic problems with the multilevel fast multipole algorithm

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2009.Thesis (Ph.D.) -- Bilkent University, 2009.Includes bibliographical references leaves 434-226.The multilevel fast multipole algorithm (MLFMA) is a powerful method for the fast and efficient solution of electromagnetics problems discretized with large numbers of unknowns. This method reduces the complexity of matrix-vector multiplications required by iterative solvers and enables the solution of largescale problems that cannot be investigated by using traditional methods. On the other hand, efficiency and accuracy of solutions via MLFMA depend on many parameters, such as the integral-equation formulation, discretization, iterative solver, preconditioning, computing platform, parallelization, and many other details of the numerical implementation. This dissertation is based on our efforts to develop sophisticated implementations of MLFMA for the solution of real-life scattering and radiation problems involving three-dimensional complicated objects with arbitrary geometries.Ergül, Özgür SalihPh.D

Fast multipole method for the solution of electromagnetic scattering problems

Cataloged from PDF version of article.The fast multipole method (FMM) is investigated in detail for the solution of electromagnetic scattering problems involving arbitrarily shaped three-dimensional conducting surfaces. This method is known to reduce the computational complexity and the memory requirement of the solution without sacrificing the accuracy. Therefore, it achieves the solution of large problems with less computational resources compared to the other traditional solution algorithms. However, the expected efficiency of the FMM may not be obtained unless the appropriate choices of the components are made. The types of the employed integral equation, iterative algorithm, and preconditioning technique directly affect the efficiency of the implementations. Performances of these components are also related to each other, and their simultaneous optimization creates a challenging task in the design of an efficient solver.Ergül, Özgür SalihM.S

Numerical Study of Chipless Tags for Radio-Frequency-Identification (RFID) Applications

We present a numerical investigation of effective chipless tags for radio-frequency-identification (RFID) applications. Chipless tags have been introduced recently as alternatives to standard tags with microchips. While they can significantly reduce the overall cost of RFID systems by eliminating microchips and procedures to mount them on tags, chipless tags bring new challenges, especially in terms of identification reliability. We focus on tag structures that consist of resonators and consider alternative scenarios to find out potential misidentification cases. We also present the robustness of resonator-type elements in terms of fabrication errors, as well as array strategies to significantly increase electromagnetic responses of tags at the cost of reduced compactness