Computational Electromagnetics and Its Applications PDF
Preview Computational Electromagnetics and Its Applications
Computational Electromagnetics and Its Applications ICASE/LaRC Interdisciplinary Series in Science and Engineering Managing Editor: MANUEL D. SALAS /CASE, NASA Langley Research Center, Hampton, Virginia, U.S.A. VolumeS Computational Electromagnetics and Its Applications edited by Thomas G. Campbell NASA Langley Research Center, Hampton, Virginia, U.S.A. R. A. Nicolaides Carnegie Mellon University, Pittsburgh, Pennsylvania, U.S.A. and Manuel D. Salas Institute for Computer Applications in Science and Engineering (/CASE), NASA Langley Research Center, Hampton, Virginia, U.S.A. SPRINGER SCIENCE+BUSINESS MEDIA, B.V. A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN 978-94-010-6354-8 ISBN 978-94-011-5584-7 (eBook) DOI 10.1007/978-94-011-5584-7 Cover Dlustration The cover illustration shows the electric surface currents on a 3. 7 wavelength sized commercial transport configuration at a single phase angle of the time harmonic solution. The surface current solution was computed at nose-on incidence with a horizontally polarized electric field (not shown). The various contours (typically shown in color) represent the magnitude of the electric currents on the body due to the electric field. Typically, the low currents are shown in the blue color range, high currents are shown by the red to white color range. This illustration was provided by Mr. Kam Hom of the NASA Langley Research Center; computed with MOM3D (NASA CR-189594), a patch method of moments, and displayed with EM-ANIMATE (NASA TM-4539), a surface current and electric field display and animation code. EM-ANIMATE can display and animate the time harmonic solution of both electric fields and surface currents in real time. Printed on acid-free paper All Rights Reserved © 1997 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 1997 Softcover reprint of the hardcover 1st edition 1997 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. TABLE OF CONTENTS Preface ............................................................... vii Keynote Presentation L. N. Medgyesi-Mitschang · .. · · ·. · ........................................ 1 Overview of EM Research in the Electromagnetic Research Branch at the Langley Research Center F. B. Beck, C. R. Cockrell, C. J. Reddy, and M. D. Deshpande ......... 15 Antenna Optimization Using the Genetic Algorithm Zwi Altman and Raj Mittra ............................................ 53 Electromagnetic Analysis for Microwave Applications J. C. Rautio ........................................................... 80 CEM for Radar Cross Section Application M. I. Sancer, G. Antilla, Y. C. Ma, and R. McClary ................... 97 Reduced-Order Electromagnetic Modeling for Design-Driven Simulations of Complex Integrated Electronic Systems A. C. Cangellaris and M. Celek ................................... 126 The True Origin of Spurious Solutions and Their A voidance by the Least-Squares Finite Element Method Bo-nan Jiang ......................................................... 155 A Note on the Use of Divergence Boundary Conditions in CEM U. Kangro and R. Nicolaides ..................................... 185 Characteristic-Based Methods in Computational Electromagnetics J. S. Shang ........................................................... 189 v vi Parallel Hierarchical Solvers and Preconditioners for Boundary Element Methods A. Grama, V. Kumar, and A. Sameh ............................. 212 Finite-Difference Time-Domain (FDTD) Computational Electrodynamics Simulations of Microlaser Cavities in One and Two Spatial Dimensions S. C. Hagness, S. T. Ho, and A. Taftove .............................. 229 Large Hybrid Finite Element Methods for Electromagnetics J. L. Volakis, J. Gong, and T. Ozdemir ............................ 252 Panel Discussion Summary and Recommendations ............. 288 List of Attendees ................................................... 308 PREFACE This volume contains the proceedings of the first ICASE/LaRC Work shop on Computational Electromagnetics and Its Applications conducted by the Institute for Computer Applications in Science and Engineering and NASA Langley Research Center. We had several goals in mind when we decided, jointly with the Elec tromagnetics Research Branch, to organize this workshop on Computa tional Electromagnetics ( CEM). Among our goals were a desire to obtain an overview of the current state of CEM, covering both algorithms and ap plications and their effect on NASA's activities in this area. In addition, we wanted to provide an attractive setting for computational scientists with expertise in other fields, especially computational fluid dynamics (CFD), to observe the algorithms and tools of CEM at work. Our expectation was that scientists from both fields would discover mutually beneficial inter connections and relationships. Another goal was to learn of progress in solution algorithms for electromagnetic optimization and design problems; such problems make extensive use of field solvers and computational effi ciency is at a premium. To achieve these goals we assembled the renowned group of speakers from academia and industry whose talks are contained in this volume. The papers are printed in the same order in which the talks were pre sented at the meeting. The first paper is an overview of work currently being performed in the Electromagnetic Research Branch at the Langley Research Center. This paper is written by Beck, Cockrell, Reddy, and Desh pande. Following this is a paper by Altman and Mittra on the application of genetic algorithms to ultra broadband antenna optimization. These algo rithms, while not necessarily inexpensive to use, are very robust, paralleliz able and easy to implement. The next paper, by Rautio is on microwave applications. He gives a careful discussion of the sources and types of er rors encountered in Method of Moment calculations for microwave circuits. This is followed by a paper by Sancer and co-workers on RCS computa tions. Their paper discusses the SWITCH code and its applications. This is a finite volume code using curvilinear hexahedral elements. The next paper by Cangellaris and Celik is concerned with reduced order modeling. This entails the use of a variety of different techniques for reducing the number vii viii of degrees of freedom required to model complex systems. Typically, these techniques can be used to interpolate or extrapolate fields for additional parameter (e.g. frequency) ranges without engaging in new full field so lutions. Jiang discusses the use of divergence boundary conditions. These provide a way to avoid the famous (or infamous) spurious mode problems encountered by simple minded finite element discretizations of Maxwell's equations. A postscript to this paper by Kangro and Nicolaides points out that there are situations where divergence boundary condition formulations are not equivalent to Maxwell's equations. The next paper, by Shang, is on the use of characteristic based solution algorithms. Of the algorithms used in CEM these are, perhaps, the ones closest to traditional CFD algorithms for hyperbolic equations. They work surprisingly well, given that they are inherently dissipative in contrast to the conservative Maxwell system. The paper by Grama, Kumar and Sameh discusses some.recent work on paral lelizing multilevel vector-matrix multiply techniques and preconditioners. They show speedups of around four orders of magnitude for problems with hundreds of thousands of variables on a 256 processor Cray T3D. The well known finite difference time domain (FDTD) algorithm is represented in the paper of Hagness, Ho and Taflove. These authors apply the algorithm to computation of fields associated with nanoscale devices such as micro lasers. The final paper by Volakis and co-authors provides a wide ranging guide to and valuable information about the application of finite elements to general electromagnetics computations. This paper intersects several of the earlier ones in that it covers reduced order techniques and parallel pro cessing as well as far boundary conditions and other topics not covered in the earlier papers. The final article contains a transcript of a panel dis cussion which was held after the talks were completed. We have minimally edited this transcript to make it clearer. Finally, there is a list of registered participants at the end of the volume. We would like to thank the speakers for their contributions to a highly successful meeting and to the other participants for their lively participation in the meeting. The editors are also grateful to M. Yousuf£ Hussaini who was involved in the early planning of this workshop. As always, Emily Todd, the !CASE Conference Manager, performed her duties in a stellar manner. We would also like to thank Shannon Keeter of !CASE for organizing a disparate collection of papers into the uniform volume you are holding in your hands. In addition, we thank Deborah Ford of NASA Langley Research Center for transcribing the results of the panel session discussions and Brian Bailie of NASA Langley Research Center for graphics support. Tom Campbell Roy Nicolaides Manny Salas KEYNOTE PRESENTATION COMPUTATIONAL ELECTROMAGNETICS: FROM THE ABACUS TO SUPERCOMPUTERS AND BEYOND L. N. MEDGYESI-MITSCHANG McDonnell Douglas Aerospace St. Louis, MO 63166 Abstract. This overview sketches key trends in computational develop ments in general and their impact on Computational Electromagnetics in particular. The ongoing changes in the aerospace industry and redirection of federal sponsorship of R & D are highlighted in this context. The opportuni ties and challenges in CEM offered by hardware and software developments are summarized. 1. Historical Retrospective The field of electromagnetics has a unique history. Its genesis lies in the far distant history of the elemental observations of the ancient Greeks. As succinctly and elegantly stated by James Clerk Maxwell in his seminal work in 1873, "A Treatise on Electricity and Magnetism," "The fact that certain bodies, after being rubbed, appear to attract other bodies, was known to ancients... Other bodies, particularly load stone ... have also been long known to exhibit phenomena of action at a distance... These two classes of phenomena (electric and magnetic) have since been found to be related to each other ... constitute the science of Electromagnetism." This was a profound statement. Few developments in science have had a greater impact than Maxwell's work. Indeed the Twentieth Century, a cen tury of advanced communication, computing and information technologies would be inconceivable without it. In the intervening century and a quarter, the knowledge in electromag netics has experienced exponential growth as measured by the number of papers published world-wide. (Fig. 1) The principal contributors following T. G. Campbell et al. (eds.), Computational ElectrrJnragnetics and Its Applications, 1-14. © 1997 Kluwer Academic Publishers. 2 L. N. MEDGYESI-MITSCHANG Maxwell were themselves giants in science. Those of us who are researchers in this field are truly standing on the shoulders of these giants and owe a great debt to these pioneers. 2. Taxonomy of Methods It is an interesting oddity of this field is that the principal focus in the last 125 years has been the solution of Maxwell's elegant compact equations. This is in contrast to many other branches of science where the central endeavor is the discovery of the governing physical laws and not their so lutions. It is customary to group the developments in electromagnetics into three periods. (Fig. 2) The first period centered on harnessing the classical meth ods of the French and German mathematicians such as Laplace, Poisson, and Gauss to solving the differential forms of Maxwell's equations. These solution techniques were based on the separation of variables and special functions. A great many canonic problems in a variety of coordinate systems were solved in this way. The work of Sommerfeld opened up new vistas that ultimately spawned the next generation of methods often termed "optic-derived" methods. The foremost pioneers of this era were Keller and Ufimtsev. Their theories of geometrical and physical diffraction addressed a whole constellation of EM phenomena in nonseparable coordinate systems that were intractable to earlier methods. The third period of developments in electromagnetics occurred in the last two decades, particularly in the last ten years. These were primarily influenced by the ubiquity of powerful computers in the form of main frames and workstations. These developments are collectively denoted to day as "numerical" methods. This designation is somewhat misleading in that the great classical mathematician such as Gauss invented many novel numerical algorithms that are central to most computer solutions of EM problems. The marriage of computers and electromagnetics has led to the term, Computational Electromagnetics ( CEM). In scope it parallels that of Computational Fluid Dynamics (CFD). The major categories of numer ical methods are the surface integral equation (SIE), the partial differential equation (PDE), and the hybrid formulations (Fig. 2) There is a vast lit erature associated with all these methods. It is outside the scope of this discussion to provide even a cursory, much less critical overview of these approaches. Among the recent CEM developments, hybrid methods are particularly promising. Building on earlier work by Thiele and co-workers, they have a number of highly beneficial attributes. Some of these are enumerated in Fig.
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