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121 Time Domain Methodsin ElectrodynamicsA Tribute to Wolfgang J. R. HoeferEditors: Peter Russer, and Uwe Siart

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Time Domain Methodsin ElectrodynamicsA Tribute to Wolfgang J. R. Hoefer

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EditorsProf. Dr. Peter RusserTU MunchenFak. Elektro- undInformationstechnikLS HochfrequenztechnikArcisstr. 2180333 MunchenGermanyrusser@ei.tum.de

Dr. Uwe SiartTU MunchenFak. Elektro- undInformationstechnikLS HochfrequenztechnikArcisstr. 2180333 MunchenGermany

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Preface

On May 16th 2007 the Faculty of Electrical Engineering and Information Tech-nology of the Technische Universitat Munchen bestowed the degree of the doctorhonoris causa to Wolfgang J.R. Hoefer for Extraordinary achievements in the theoryof electromagnetic fields. On this special occasion a symposium on Time DomainMethods in Modern Engineering Electrodynamics has been held in honor of Pro-fessor Wolfgang J.R. Hoefer at the Technische Universitat Munchen on May 16and 17, 2007. The symposium topic was focused on the main area of research ofWolfgang J.R. Hoefer, the time domain methods in computational electromagneticsespecially the transmission line matrix method and its applications. The transmis-sion line matrix method has been developed and first published by Johns and Beurlein 1971. In the past 20 years Wolfgang Hoefer has given exemplary contributions tothe development of the transmission line method.

Space and time discretizing time domain methods have emerged as key numeri-cal methods in computational electromagnetics. Time domain methods are versatileand can be applied to the solution of wide range of electromagnetic field prob-lems. Computing the response of an electromagnetic structure to an impulsive ex-citation localized in space and time provides a comprehensive characterization ofthe electromagnetic properties of the structure in a wide frequency range. The mostimportant methods are the finite difference time domain and the transmission linematrix methods. Whereas finite difference methods are based on the transition fromdifferentials in the Maxwells Equations to finite differences, the transmission linematrix (TLM) method is based on the representation of the discretized electromag-netic by wave pulses propagating in a three-dimensional mesh of transmission lines.The space is discretized by subdivision into cells and the electromagnetic field ismodeled by wave pulses propagating between adjacent cells and scattered withinthe cells. The TLM algorithm is based on the modeling of the propagation of wavepulses through a mesh of transmission lines and the scattering of the wave pulsesand in mesh nodes. The simulation of the reaction to a single impulsive electro-magnetic excitation yields a large amount information. The versatility of the TLMmethods allows straightforward calculation of complex electromagnetic structures.With the computational power of today’s computers, this method is a powerful toolfor the computer-aided design of complex electromagnetic structures.

The symposium has given the opportunity to colleagues and students of WolfgangJ.R.Hoefer topresent their recentadvances in thefieldof timedomainelectromagnetics

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and its applications. This book contains extended versions of most of the scientificcontributions of the symposium. The arrangement of the contributions in five chap-ters corresponds to the allocation of the presented material into five sessions.

1. Time-Domain Methods for Electromagnetic Field Modelling2. The Transmission-Line-Matrix Method3. Circuit Concepts and Methods4. Antenna and Ultrawideband System Design5. Novel Devices and Systems

The first chapter deals with time-domain methods for electromagnetic modelingin general. The second chapter focuses on the TLM method. The third chapter isdedicated to network concepts applied to electromagnetic field modeling. The fourthchapter is dedicated to circuit and system applications, and the fifth chapter dels withbroadband devices, systems and measurement techniques.

The honorary doctor degree bestowal ceremony took place in the morning of 16May 2007. In the beginning of the bestowal ceremony addresses of Professor UlrichWagner, the dean on the Faculty of Electrical Engineering and Information Tech-nology of the Technische Universitt Mnchen, and Professor Wolfgang A. Hermann,the president of the Technische Universitt Mnchen were given. After this ProfessorPeter Russer held the laudatio. This was follwed by the bestowal and the lectio ofWolfgang J.R. Hoefer.

Munich, Peter RusserDecember 2007 Uwe Siart

Laudatio on Professor Wolfgang J.R. Hoefer

Peter Russer

The Faculty of Electrical Engineering and Information Technology of the Tech-nische Universitt Munchen bestows the Honorary Doctor degree on ProfessorDr. Wolfgang Hoefer for extraordinary scientific achievements in the theory of elec-tromagnetic fields. Since many years Professor Wolfgang Hoefer is one of theinternationally outstanding scientists in the area of numerical methods for electro-magnetic field computation. He has given fundamental contributions in the field oftechnical applications of the electromagnetic theory. In particular he has pioneeredthe development of the transmission line matrix (TLM) method, an efficient compu-tational tool for the numerical computation of electromagnetic fields by numerouscontributions.

Wolfgang Hoefer was born in 1941 in the Rhineland. He received the Dipl.-Ing.degree from the Rheinisch Westflische Technische Hochschule in Aachen and theDocteur Ingenieur degree from the Universit Grenoble. Subsequently he becameResearch Fellow at the Institut Nationale Polytechnique de Grenoble.

In 1969 Wolfgang Hoefer firstly became Assistant Professor at the Universityof Ottawa, Canada. In 1975 he became there Associate Professor and in 1980 FullProfessor. In 1992 he was appointed to a professorship at the NSERC Industrial Re-search Chair in RF Engineering at the University of Victoria, B.C. Canada. Therehe led the Computational Electromagnetics Research Laboratory (CERL) at the De-partment of Electrical and Computer Engineering until his retirement in July 2006.

In 1996 Professor Hoefer founded the Faustus Scientific Corporation. This spin-off company develops professional electromagnetic field simulation CAD tools forresearch, development and education in the area of radio frequency analog circuitsand high-speed digital circuits.

Professor Hoefer has given pioneering contributions to the development of timedomain methods for the numerical computation of electromagnetic fields. He hasbeen among the worldwide first scientists who applied the finite difference timedomain method for the numerical modeling of waveguide structures and distributedmicrowave circuits.

P. RusserInstitute for High Frequency Engineering, Technischen Universitat Munchen,e-mail: russer@tum.de

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x P. Russer

In these areas Professor Hoefer contributed more than 150 publications in in-ternational scientific journals and more than 250 contributions to internationalconferences. The book Microwave Circuit Modeling Using Electromagnetic FieldSimulation, which he published in 2003 together with D.G. Swanson, presents thetheoretical fundamentals und methods of the design of microwave circuits by meansof electromagnetic CAD tools.

His contributions to the development of the TLM method are seminal [1, 2].He has been the first who modeled dispersive materials in time domain. Moreoverhe developed novel methods for the field-based synthesis of optimum microwavestructures and methods for the generation of compact circuit models based upon thefield modeling of circuits.

In the areas of electromagnetic theory and numerical methods of electromagneticfield modeling Professor Hoefer acted successfully as educator and guided numer-ous young PhD students to success. In 2006 he received the Distinguished EducatorAward of the IEEE MTT Society.

In his research areas Wolfgang Hoefer gained internationally highest recognition.He is Fellow of the IEEE and Fellow of the ASI (Advanced Systems Institute ofBritish Columbia). In 2003 he has been elected Fellow of the Royal Society ofCanada. He is member of numerous scientific committees and boards and he is co-founder and editor of the International Journal of Numerical Modelling.

Since 1990 Professor Hoefer is closely related to the Institute for High FrequencyEngineering by a continuous scientific cooperation. Within this cooperation numer-ous joint scientific publications resulted. Professor Hoefer has been Visiting Pro-fessor at our institute in 1991 and 1999 and this year he is again Visiting Professorfrom April to July.

To fully appraise Wolfgang Hoefers contributions to the electromagnetic theoryas a scientist and as an educator we first of all take a look at some peculiarities of thisarea. On the one hand the electromagnetic theory requires mathematical strictnessand abstraction, on the other hand creativity in this field is especially promoted byimagery thinking.

Maxwell’s theory establishes the analytic and conceptual framework of electro-magnetism. As an analytic tool it allows the mathematical modeling of the electro-magnetic field in even complex structures. However, prior to this Maxwell’s theoryallows the construction of concepts and also is the basis of mental imagery. HeinrichHertz wrote in his treatise on Maxwell’s equations of electromagnetism:

One cannot escape the feeling that these mathematical formulae have an independent exis-tence and an intelligence of their own, that they are wiser than we are, wiser even than theirdiscoverers, that we get more out of them than was originally put into them [3,4].

In scientific research mental imagery plays an essential role. In natural sciencesknowledge is constructed on the basis of experimental experience. According toHenri Poincar the mind contains two synthetic a priori intuitions that organize per-ception into knowledge – the principle of mathematical induction and the intuitionof continuous groups that exists in our mind prior to all experience.

Theories are created by invention and not by discovery. Einstein took the viewthat the axiomatic structure of a theory is built psychologically on the experiences

Laudatio on Professor Wolfgang J.R. Hoefer xi

of the world of perceptions. In his inaugural speech at the Royal Prussian Academyof Science on 2nd July 1914 Albert Einstein said:

Die Methode des Theoretikers bringt es mit sich, dass er als Fundament allgemeine Vo-raussetzungen, so genannte Prinzipe, benutzt, aus denen er Folgerungen deduzieren kann.Seine Ttigkeit zerfllt also in zwei Teile. Er hat erstens jene Prinzipe aufzusuchen, zweitensdie aus den Prinzipen flieenden Folgerungen zu entwickeln. Fur die Erfullung der zweitender genannten Aufgaben erhlt er auf der Schule ein treffliches Rustzeug. Wenn also dieerste seiner Aufgaben auf einem Gebiete bzw. fur einen Komplex von Zusammenhngenbereits gelost ist, wird ihm bei hinreichendem Flei und Verstand der Erfolg nicht fehlen.Die erste der genannten Aufgaben, nmlich jene, die Prinzipe aufzustellen, welche der De-duktion als Basis dienen sollen, ist von ganz anderer Art. Hier gibt es keine erlernbare,systematisch anwendbare Methode, die zum Ziele fuhrt. Der Forscher muss vielmehr derNatur jene allgemeinen Prinzipe gleichsam ablauschen, indem er an groeren Komplexenvon Erfahrungstatsachen gewisse allgemeine Zuge erschaut, die sich scharf formulierenlassen [5].

Fig. 1 The President of the Technische Univesitat Munchen Wolfgang A. Herrmann and WolfgangJ.R. Hoefer

The method of the theoretician involves that he uses general conditions, so-called principlesas a basis and to draw the conclusions from there. He first has to find these principles andthen to develop the conclusions from there. To fulfill the second task he receives a suitabletool in school. If the first of his tasks already has been solved in an area or for a contex-tual complex, sufficient diligence and intelligence will yield success. The first mentionedtask to establish the principles, which will serve as a basis for deduction is of completelydifferent nature. Here no successful systematic method can be learnt. On the contrary theresearcher has to listen to nature’s general principles by recognizing general patterns thatcan be formulated strictly in large complexes of empirical facts. (Translation by the author)

These abilities mentioned by Einstein first to find the principles underlying thephenomena and then to develop the conclusions from there characterize WolfgangHoefer impressingly and are the basis not only of his extraordinary scientific cre-ativity but also of his exceptional aptitude as an educator. In his scientific work

xii P. Russer

Professor Hoefer has shown remarkable creativity up to the present. His scientificachievements are extraordinary by any standard. His name stands for pioneeringcontributions to the theory of electromagnetic waves and their applications overa period of more than forty years. In the theory of electromagnetic waves, theirtechnological application and academic teaching, he is an outstanding internationalscientific figure.

For our faculty the bestowal of the honorary doctorate on Professor WolfgangHoefer is an event of great significance and pleasure.

References

1. W. Hoefer, “The transmission line matrix method-theory and applications,” IEEE Trans.Microw. Theory Techn., vol. 33, pp. 882–893, Oct. 1985.

2. W. Hoefer, “The transmission line matrix (TLM) method,” in Numerical Techniques for Mi-crowave and Millimeter Wave Passive Structures (T. Itoh, ed.), pp. 496–591, New York:J. Wiley., 1989.

3. H. Hertz, Gesammelte Werke, Bd. 2, Untersuchungen uber die Ausbreitung der elektrischenKraft. Johann Ambrosius Barth Leipzig 1894.

4. F. Wilczeck, “A piece of magic – the Dirac equation,” in It must be Beautiful – Great Equationsof Modern Science (G. Farmelo, ed.), London, New York: Granta, 2002.

5. A. Einstein, “Antrittsrede des Herrn Einstein,” Sitzungsberichte der koniglich preußischenAkademie der Wissenschaften, vol. SB II, pp. 739–742, July 1914.

Contents

Laudatio on Professor Wolfgang J.R. Hoefer . . . . . . . . . . . . . . . . . . . . . . . . . ixPeter Russer

In Search of the Intangible – 43 Years of Research in Electromagnetics . . 1Wolfgang J.R. Hoefer

Full-Wave Simulation of Integrated Circuit Packages on a ParallelArchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Erion Gjonaj, Andreas Barchanski, Peter Thoma and Thomas Weiland

Recent Progress in Unifying the Time- and Frequency-Domain Methods . 31Zhizhang (David) Chen and Michel M. Ney

Time-Domain Neural Network Approaches to EM Modeling ofMicrowave Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Qi-Jun Zhang and Yi Cao

Modeling of Curved Boundaries in the Finite-Difference Time-DomainMethod using a Lagrangian Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Johannes A. Russer, Prasad S. Sumant and Andreas C. Cangellaris

Computing the Transmission Line Parameters of an On-chipMulticonductor Digital Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Hristomir Yordanov and Peter Russer

Two Decades of SCN Modelling and Beyond . . . . . . . . . . . . . . . . . . . . . . . . . 79Dr. Poman So, P. Eng.

Calculation of Instantaneous Power and Energy Quantities in TLMSimulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91John Paul, Christos Christopoulos, and David W. P. Thomas

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The Combined Schrodinger-Maxwell Problemin the Electronic/Electromagnetic Characterization of Nanodevices . . . . . 105Luca Pierantoni, Davide Mencarelli and Tullio Rozzi

Recent Advances in the Combination of the Unscented Transform (UT)with the Transmission Line Modeling Method (TLM) . . . . . . . . . . . . . . . . . 135Leonardo R.A.X de Menezes, Ajibola Ajayi, Christos Christopoulos,Phillip Sewell and Geovany A. Borges

Bandwidth Optimization using Transmission Line Matrix Modeling andSystem Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147Nikolaus Fichtner, Uwe Siart, Yury Kuznetsov, Andrey Baev and PeterRusser

Study of Single and Dual Band Wearable Metallic Button Antennas forPersonal Area Networks (PANs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Benito Sanz-Izquierdo, Fengxi Huang, John C. Batchelorand Mohammed I. Sobhy

Fast and Efficient Methods for Circuit-based Automotive EMCSimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Martin L. Zitzmann and Robert Weigel

Equivalent Circuit (EC) FDTD Method for Dispersive Materials:Derivation, Stability Criteria and Application Examples . . . . . . . . . . . . . . . 211A. Rennings, A. Lauer, C. Caloz and I. Wolff

A 3D Isotropic Left-Handed Metamaterial Based on the Rotated TLMScheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239M. Zedler, C. Caloz and P. Russer

Connection Subnetworks for the Transmission Line Matrix (TLM)Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263Petr Lorenz and Peter Russer

RFID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283Li Yang, Amin Rida, Anya Traille and Manos M. Tentzeris

Numerical Modeling of Car Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303Stefan Lindenmeier and Joachim Brose

Time-Domain Modelling of Group-Delay and Amplitude Characteristicsin Ultra-Wideband Printed-Circuit Antennas . . . . . . . . . . . . . . . . . . . . . . . . 321Hung-Jui Lam, Yinying Lu, Huilian Du, Poman P.M. So and Jens Bornemann

On the Modeling of Ultra Wide Band (UWB) Radiating Structures . . . . . . 333Bruno Biscontini, Uwe Siart and Peter Russer

Contents xv

An Efficient Electromagnetically Optimized Design and Realization ofPseudo-Elliptic All-Metal Cavities Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . 345Dr. Savvas Kosmopoulos and Nikolaos Sidiropoulos

Simulation of Coplanar Devices Accessing Nano Systems . . . . . . . . . . . . . . 361F. Peretti, G. Csaba and P. Lugli

Time-Domain Measurements of Electromagnetic Interference . . . . . . . . . . 375Stephan Braun, Arnd Frech and Peter Russer

Space Mapping Optimization and Modeling of Microwave Devices withMEFiSTo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393Slawomir Koziel and John W. Bandler

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

List of Contributors

Ajibola AjayiThe George Green Institute for Electromagnetics Research, University Park,Nottingham, NG7 2RD, UK, e-mail: eezks@gwmail.nottingham.ac.uk

Andrey BaevMoscow Aviation Institute (State Technical University) Volokolamskoe sh. 4, A-80,GSP-3, Moscow, 125993, Russia, e-mail: baev@mai-trt.ru

John W. BandlerMcMaster University, Hamilton, ON, Canada L8S 4K1,e-mail: bandler@mcmaster.ca

Andreas BarchanskiInstitut fur Theorie Elektromagnetischer Felder, Technische Universitat Darmstadt,Schlossgartenstr. 8, 64289 Darmstadt, Germany, e-mail: barchanski@temf.de

John C. BatchelorDepartment of Electronics, The University of Kent, Canterbury, Kent, UK,CT2 7NT, e-mail: j.c.batchelor@kent.ac.uk

Bruno BiscontiniMunch University of Technology, Institute for High Frequency Engineering,Arcisstr. 21 80333, Munich Germany, e-mail: bicontini@mytum.de

Geovany A. BorgesDep. de Eng. Eletrica - Universidade de Brasılia, CEP 70910-919 – Brasılia – DF,Brazil

Jens BornemannDepartment of Electrical and Computer Engineering, University of Victoria,P.O. Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada

Stephan BraunInstitute for High-Frequency Engineering, Technische Universitat Munchen,Germany, e-mail: stephan.braun@tum.de

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xviii List of Contributors

Joachim BroseInstitute for High Frequency Technology, Faculty for Electronics and InformationTheory, Bundeswehr University, Munich, 85577 Neubiberg, Germany

C. CalozEcole Polytechnique, Montreal, Canada, e-mail: christophe.caloz@polymtl.ca

Andreas C. CangellarisDepartment of Electrical and Computer Engineering, University of Illinois atUrbana-Champaign, USA

Andreas C. CangellarisDepartment of Electrical and Computer Engineering, University of Illinois atUrbana-Champaign, USA

Yi CaoDept of Electronics, Carleton University, 1125 Colonel By Dr., Ottawa, CanadaK1S 5B6

Zhizhang (David) ChenDepartment of Electrical and Computer Engineering, Dalhousie University,Halifax, Canada, e-mail: z.chen@dal.ca

Christos ChristopoulosThe George Green Institute for Electromagnetics Research, School of Electrical andElectronic Engineering, University of Nottingham, University Park, Nottingham,NG7 2RD, UK, e-mail: eezks@gwmail.nottingham.ac.uk

G. CsabaInstitute for Nanoelectronics Technical University of Munich, D-80333 Munich,Germany

Leonardo R.A.X de MenezesDep. de Eng. Eletrica – Universidade de Brasılia, CEP 70910-919 – Brasılia - DF,e-mail: Brazil,leonardo@ene.unb.br

Huilian DuDepartment of Electrical and Computer Engineering, University of Victoria,P.O. Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada

Nikolaus FichtnerInstitute for High-Frequency Engineering, Technische Universitat Munchen,Arcisstr. 21, 80333 Munchen, Germany, e-mail: fichtner@tum.de

Arnd FrechInstitute for High-Frequency Engineering, Technische Universitat Munchen,Germany, e-mail: frech@tum.de

Erion GjonajInstitut fur Theorie Elektromagnetischer Felder, Technische Universitat Darmstadt,Schlossgartenstr. 8, 64289 Darmstadt, Germany, e-mail: gjonaj@temf.de

List of Contributors xix

Wolfgang J. R. HoeferDepartment of Electrical and Computer Engineering, University of Victoria,Victoria, BC V8W 3P6 Canada, e-mail: whoefer@ece.uvic.ca

Fengxi HuangFormerly with the Department of Electronics, The University of Kent, Canterbury,Kent, UK, CT2 7NT

Dr. Savvas KosmopoulosSpace Engineering S.p.A., via dei Berio No.91, 00155, Rome, Italy

Slawomir KozielMcMaster University, Hamilton, ON, Canada L8S 4K1,e-mail: koziels@mcmaster.caNow with Reykjavik University, Reykjavik, Iceland, e-mail: koziel@ru.is

Yury KuznetsovMoscow Aviation Institute (State Technical University) Volokolamskoe sh. 4, A-80,GSP-3, Moscow, 125993, Russia, e-mail: kuznetsov@mai-trt.ru

Hung-Jui LamDepartment of Electrical and Computer Engineering, University of Victoria,P.O. Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada

A. LauerIMST GmbH, D-47475 Kamp-Lintfort, Germany

Stefan LindenmeierInstitute for High Frequency Technology, Faculty for Electronics and InformationTheory, Bundeswehr University, Munich, 85577 Neubiberg, Germany

Petr LorenzRohde&Schwarz GmbH & Co. KG, Muhldorfstr. 15, 81671 Munchen, Germany,e-mail: petr.lorenz@ieee.org

Yinying LuDepartment of Electrical and Computer Engineering, University of Victoria,P.O. Box 3055 STN CSC, Victoria, B.C., V8W 3P6, Canada

P. LugliInstitute for Nanoelectronics Technical University of Munich, D-80333 Munich,Germany

Davide MencarelliDipartimento di Elettromagnetismo e Bioingegneria - Universita Politecnica delleMarche, Ancona 60100, Italy, e-mail: d.mencarelli@univpm.it

Michel M. NeyTelecom Breta Institute, Brest, France, e-mail: michel.ney@telecom-bretagne.eu

John PaulGeorge Green Institute for Electromagnetics Research, School of Electrical andElectronic Engineering, University of Nottingham, Nottingham, NG7 2RD, UK,e-mail: john.paul@nottingham.ac.uk

xx List of Contributors

F. PerettiInstitute for Nanoelectronics Technical University of Munich, D-80333 Munich,Germany

Luca PierantoniDipartimento di Elettromagnetismo e Bioingegneria – Universita Politecnica delleMarche, Ancona 60100, Italy, e-mail: l.pierantoni@univpm.it

A. RenningsIMST GmbH, D-47475 Kamp-Lintfort, Germany, e-mail: A.Rennings@ieee.org

Amin RidaGeorgia Electronic Design Center, School of Electrical and Computer Engineering,Georgia Institute of Technology, Atlanta, GA 30332-0250, USA

Tullio RozziDipartimento di Elettromagnetismo e Bioingegneria - Universita Politecnica delleMarche, Ancona 60100, Italy, e-mail: t.rozzi@univpm.it

Johannes A. RusserDepartment of Electrical and Computer Engineering, University of Illinois atUrbana-Champaign, USA

Peter RusserMunich University of Technology, Institute for High Frequency Engineering,Technische Universitat Munchen, Arcisstr. 21, 80333 Munich, Germany,e-mail: russer@tum.de

Benito Sanz-IzquierdoDepartment of Electronics, The University of Kent, Canterbury, Kent, UK,CT2 7NT, e-mail: b.sanz@kent.ac.uk

Phillip SewellThe George Green Institute for Electromagnetics Research, University Park,Nottingham, NG7 2RD, UK, e-mail: eezks@gwmail.nottingham.ac.uk

Uwe SiartMunch University of Technology, Institute for High Frequency Engineering,Technische Universitat Munchen, Arcisstr. 21 80333, Munich Germany,e-mail: uwe.siart@tum.de

Nikolaos SidiropoulosSpace Engineering S.p.A., via dei Berio No.91, 00155, Rome, Italy

Poman P.M. SoDepartment of Electrical Engineering, Department of Electrical and ComputerEngineering, University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC,Canada, V8W 3P6, e-mail: Poman.So@ECE.UVic.CA

Mohammed I. SobhyDepartment of Electronics, The University of Kent, Canterbury, Kent, UK,CT2 7NT

List of Contributors xxi

Prasad S. SumantDepartment of Electrical and Computer Engineering, University of Illinois atUrbana-Champaign, USA

Manos M. TentzerisGeorgia Electronic Design Center, School of Electrical and Computer Engineering,Georgia Institute of Technology, Atlanta, GA 30332-0250, USA

Peter ThomaInstitut fur Theorie Elektromagnetischer Felder, Technische Universitat Darmstadt,Schlossgartenstr. 8, 64289 Darmstadt, Germany; Computer Simulation TechnologyGmbH, Bad Nauheimerstr. 19, 64289 Darmstadt, Germany,e-mail: peter.thoma@cst.com

David W. P. ThomasGeorge Green Institute for Electromagnetics Research, School of Electrical andElectronic Engineering, University of Nottingham, Nottingham, NG7 2RD, UK

Anya TrailleGeorgia Electronic Design Center, School of Electrical and Computer Engineering,Georgia Institute of Technology, Atlanta, GA 30332-0250, USA

Robert WeigelInstitute for Electronics Engineering, University of Erlangen-Nuremberg,Cauerstrasse 9, 91058 Erlangen, Germany, e-mail: weigel@lfte.de

Thomas WeilandInstitut fur Theorie Elektromagnetischer Felder, Technische Universitat Darmstadt,Schlossgartenstr. 8, 64289 Darmstadt, Germany, e-mail: thomas.weiland@temf.de

I. WolffIMST GmbH, D-47475 Kamp-Lintfort, Germany

Li YangGeorgia Electronic Design Center, School of Electrical and Computer Engineering,Georgia Institute of Technology, Atlanta, GA 30332-0250, USA

Hristomir YordanovMunich University of Technology, Institute for High Frequency Engineering,Arcisstr. 21, 80333 Munich, Germany, e-mail: yordanov@tum.de

M. ZedlerTechnische Universitat Munchen, Germany, e-mail: michael.zedler@tum.de

Qi-Jun ZhangDepartment of Electronics, Carleton University, 1125 Colonel By Dr., Ottawa,Canada K1S 5B6

Martin L. ZitzmannBMW Group, Development Ignition Systems, Hufelandstrasse 4, 80788, Munich,Germany, e-mail: Martin-Ludwig.Zitzmann@bmw.de

In Search of the Intangible – 43 Yearsof Research in Electromagnetics

Wolfgang J.R. Hoefer

Magnifizenz, Spektabilitat, Professor Russer, Honored Guests, Ladies andGentlemen:

This is a day of great honor and deep emotions. Receiving this honorary doctoratefrom the prestigious Technische Universitat Munchen is not only a splendid profes-sional accolade, but also a deeply gratifying and humbling distinction, bestowed onme by one of the leading academic institutions of my native country.

1 Words of Appreciation and Gratitude

I wish to open this lecture with heartfelt words of appreciation and gratitude. Firstand foremost, I thank the academic leaders of this university, President Herrmann,Dean Wagner, and the distinguished members of Faculty Council, for honoring mebeyond all expectations. My sincere gratitude and admiration go to my colleagueand friend, Professor Peter Russer, not only for initiating and promoting the be-stowal process, but also for being my trusted colleague, inspiring fellow researcher,loyal friend and gracious host at his Institute of High Frequency Engineering forover twenty years. Speaking of divine justice – I was delighted to learn that hehimself received a well-deserved honorary doctorate from the renowned MoscowUniversity of Aerospace Technologies (MAI) less than a month ago.

This is the right time to pay tribute to all those who, through their love, sup-port, friendship and collaboration have sustained and enriched my life and career.They deserve a significant share of the honor and recognition I receive today. Mymother, in spite of her 91 years, did not hesitate to travel all the way from Koblenzto Munchen so she could celebrate this event with us. After my father perished inthe war in 1944, she single-mindedly and at considerable personal sacrifice, ensuredthat my sister and I received the best possible education. Without her unfailing love

Wolfgang J.R. HoeferDepartment of Electrical and Computer Engineering, University of Victoria, Victoria, BC V8W3P6 Canada, e-mail: whoefer@ece.uvic.ca

P. Russer, U. Siart (eds.), Time Domain Methods in Electrodynamics, 1c© Springer-Verlag Berlin Heidelberg 2008

2 W.J.R. Hoefer

and determination this bestowal would not have taken place. I am also indebtedto my sister Marlies and her family for their unconditional support. My dear wifeDiana has redefined my life in more than one way and deserves a special doctorateof her own – amoris causa! My children Christian and Elise who cannot be with ustoday, have always been loving and supportive, even though I had to be away onmany of their birthdays or special school events. So many colleagues, associates,students and friends have shared their talents and insights with me over all theseyears that it is impossible to mention them all, but I would like to single out Profes-sor Poman So who has been the keystone of my research team for more than twentyyears. His exceptional talent for bringing electromagnetic fields alive on a computerhas significantly shaped and enabled the evolution of our research and was critical tothe development of the commercial electromagnetic simulator MEFiSTo. To Pomanand to all my former students and associates, several of them present among us to-day, go my sincere feelings of gratitude and appreciation. I am delighted to sharethis honor with all of you!

2 The Intangible

Let me preface the account of my search for the Intangible with these mysticalwords:

Durch alle Tone tonetIm bunten ErdentraumEin leiser Ton gezogenFur den, der heimlich lauschet.

Beneath the thousand soundsOf Earth’s colorful dreamThere rings a constant gentle toneFor all who secretly listen.

This motto, taken from a poem by the romantic philosopher and poet Friedrichvon Schlegel (1722–1829), is usually cited in connection with one of RobertSchumann’s most ambitious piano works, the Fantasy in C Major, Op. 17. Likemany works of poetry, these lines transcend their immediate context and convey amuch deeper insight. Clearly, they capture the essence of romanticism and appearto relate more to the esoteric than to the scientific. However, I could not think ofa more fitting way to describe the secret attraction that entices not only the artistbut also the scientific researcher to reach for the Intangible. Research is not merelya professional occupation but a life-long passion and commitment. Its evolution istherefore closely intertwined with the phases of the human existence. Again I havechosen a rather romantic aphorism – not entirely without tongue-in-cheek – namelya series of four paintings by Thomas Cole (1801–1848) titled “The Voyage of Life”to paraphrase this evolution. I leave it to you to make your own connections betweenThomas Cole’s paintings and my journey as we go along.

In Search of the Intangible 3

The Voyage of Life series is an allegory of the four stages of life: childhood,youth, adulthood, and old age. In each painting, accompanied by a guardian angel,the voyager rides in a boat on the River of Life. The landscapes, depicting the sea-sons of the year, play a major role in telling the story. In childhood, the infant glidesfrom a dark cave into a rich, green pasture full of promise (Fig. 1). As a youth(Fig. 2), the voyager takes control of the boat and aims for a shining castle in thesky, a vivid symbol of the Intangible that exerts an irresistible attraction upon thevoyager and propels him forward. The attentive viewer will note that the river soontakes an ominous turn towards distant cliffs and treacherous rapids. In adulthood,(Fig. 3) the voyager relies on prayer, faith and steadfastness to sustain him throughrough waters and a threatening landscape. As the voyager reaches old age, the angelguides him to heaven across the waters of eternity (Fig. 4). He is still reaching forsomething intangible, which is now more meta-physical in nature than the shiningcastle of youth.

Fig. 1 The Voyage of Life – Childhood

Fig. 2 The Voyage of Life – Youth

4 W.J.R. Hoefer

Fig. 3 The Voyage of Life – Adulthood

Fig. 4 The Voyage of Life – Old Age

In spite of their religious and moral intent, these allegoric paintings strongly res-onate with anyone who contemplates the human condition. On a lighter note, theyremind us gently but firmly that we are inevitably approaching that fourth phase inour lives by the time we receive an honorary doctorate.

3 First Steps

My own “Voyage of Life” began in 1941 in Urmitz, a small village on the westernborder of the river Rhine. I still remember posing for the picture Fig. 5 at age sevenwith my sister Marlies. We were given something to do, so the picture would lookmore natural. While my sister was occupied with weaving two-dimensional patterns,

In Search of the Intangible 5

Fig. 5 First attempts at 3D modeling

I am shown here making my first attempts at three-dimensional modeling usinguniform finite building blocks. Obviously, this picture turned out to be somewhatprophetic.

4 Studies at the RWTH Aachen

In October 1959 I began my studies of Electrical and Communications Engineeringin Aachen, the former Imperial City of Charlemagne. From early on I felt very muchattracted by the intangible nature of electric and magnetic fields and their ability totransmit information and energy. I wrote my engineering diploma thesis in ProfessorDoring’s Institut fur Hochfrequenztechnik, on a project to fabricate rotational ferriteellipsoids of various aspect ratios, and to predict and measure their interaction withelectromagnetic fields in rectangular waveguide components.

The bottles on the table in Fig. 6a suggest a chemistry lab rather than a microwavelab, but since my lab coat is not white but grey, I cannot be a chemist. The liquidsare simply fluids for cleaning the tiny ferrite samples I am making, and the verticaltubes at the back of the table form part of a home-made differential control systemto stabilize the air pressure for the grinding mill shown in Fig. 7. The drawing on thewall, reproduced again in Fig. 6b, shows the magnetic coupling between a standingTE10 wave in the horizontal guide and the two vertical guides through couplingslots via the magnetized ferrite sample. This was the arrangement to be calculated,realized and measured.

The mill for grinding the ferrite samples was a cylindrical pillbox covered insidewith fine sandpaper (Fig. 7). Compressed air enters tangentially through a narrowhole and exits through the perforated side walls of the mill. A small cylindricalferrite sample would normally be ground down to a sphere in about an hour, butin order to obtain an oblong ellipsoid, I placed the mill between the poles of astrong electro-magnet. Careful control of air pressure, field strength and grindingtime yielded an ellipsoid of desired aspect ratio.

6 W.J.R. Hoefer

(a) (b)

Fig. 6 (a) Making gyromagnetic ferrite ellipsoids; (b) Waveguide cross-coupler with ferriteellipsoid

Fig. 7 A mill for grinding perfect ellipsoids. A DC magnetic field determines the ellipticity

In the early 1960’s most of the electronic and mechanical components of an ex-perimental arrangement had to be hand-made. For this project I needed to controlthe pressure of the air at the ferrite mill to ensure consistent results. In Fig. 8 I ambuilding my own air pressure control unit. Some interesting examples of electronicand microwave equipment available at the time can be seen here as well. In the end,everything worked perfectly, and I got my engineering diploma. But what should Ido next?

In Search of the Intangible 7

Fig. 8 Building the air pressure control unit

5 Doctoral Studies at the Universite de Grenoble

I was not yet ready for a nine-to-five job. My idea was to continue the free life of astudent, but with a different dimension. So I explored the possibility of a graduatescholarship in France, and ended up in Grenoble on February 9, 1966, just three daysafter turning 25. I really liked my new environment and had a great time in France,but I still needed to decide on a topic of study. I first looked into computer engi-neering and informatics, a field that was in full expansion at that time, but I finallygravitated towards the “Laboratoire d’Electromagnetisme” which was linked to thereputed “Institut Joseph Fourier”, where I could conduct research on my favoritetopic of electromagnetics and microwaves.

Researchers at the French National Scientific Research Center (CNRS) had de-veloped a technology for fabricating Yttrium-Iron Garnet (YIG) spheres of excep-tional purity and surface quality. The resonant bandwidth of these spheres was sonarrow that it could not be measured with available instrumentation. My task was tocreate a measurement system that was sensitive enough to measure resonant band-widths as narrow as several tenths of an Oersted. I first needed to build a very stableX-band source, shown in Fig. 9 against a blackboard with a drawing of the RF partof the stabilizer, that included a high-Q cavity discriminator driving a differentialcontrol amplifier. All components, from the cavity to the amplifier, were to be de-signed and made in-house (Fig. 10).

The complete measurement system required a cart with three shelves, and itworked perfectly: it down-converted the swept microwave response of a cavity con-taining the YIG sphere to 30 MHz and compared it to the response of a calibratedresonant circuit of adjustable Q-factor. The experimental technique was based on theanalysis of coupling between an electromagnetic cavity and a YIG sphere of verynarrow bandwidth, described in my first paper titled Couplage d’une cavite electro-magnetique avec un echantillon de grenat a raie tres etroite (Coupling between anelectromagnetic cavity and a garnet sample of very narrow resonant bandwidth). It

8 W.J.R. Hoefer

Fig. 9 A stabilized klystron X-band source

Fig. 10 Complete Q-factor measurement system

In Search of the Intangible 9

was published in the Transactions of the French Academy of Sciences. Each transac-tion paper must be sponsored and transmitted by one of the members of the FrenchAcademy. My sponsor was Professor Louis Neel who, three years later, receivedthe Nobel Prize in Physics for his work on the nature and properties of ferrites.Naturally, I was very proud of this paper and the prestigious circumstances of itspublication (Fig. 11).

The design of the cavities and the analysis of the field interaction between thecavities and the YIG samples required some advanced electromagnetic modeling,but the available computational tools of the day were just as elementary as the labo-ratory equipment and included the slide rule, tables of logarithms, trigonometric andhigher mathematical functions, and collections of formulae and integrals. A digitalcomputer could only be found in the computing center. A FORTRAN program waspunched into a stack of perforated cards and fed to the compiler. The results cameback a day or two later, printed on yards and yards of paper, that had a tendency toaccumulate into large piles in students’ offices. I remember submitting a program for

Fig. 11 Measuring theQ-factor of a high qualityYIG sphere

10 W.J.R. Hoefer

finding the first root of a transcendental equation that involved Bessel and Neumannfunctions. When I returned the next day I found my pile of perforated cards with anote that my job had been rejected because it required more than 12 K of RAM. Ineeded to get a special permission from the director of the computing center to runsuch a computationally intensive job.

6 Teaching and Research at the University of Ottawa

When I completed and defended my doctoral thesis in June 1968, France was inupheaval. Student protests and general strikes paralyzed the country. After one yearof postdoctoral research and teaching in Grenoble I was definitely ready to moveon. At that time, Canada had entered a phase of intense economic and social devel-opment which made it highly attractive to start an academic career in that country.So I decided to embark upon the big journey across the Atlantic, bought a one-wayairplane ticket, and on August 4, 1969, landed in Ottawa with two suitcases, an em-ployment contract with the University of Ottawa, and four hundred dollars in mypocket, just two weeks after the first landing of man on the moon. Unlike the Astro-nauts I wanted to stay at my destination for at least one year. As we know now, thatguess was very wrong.

7 New Challenges

The transition from the role of student to the role of teacher and researcher, fromthe well-established institutionalized European environment to the evolving andcompetitive North-American system, and from the old to the new world, presentednumerous challenges. In particular, when faced with the mandate to develop newcourses in microwaves and electromagnetics and to build an infrastructure for cut-ting edge research, questions arose that I had not given much thought before. Theyranged from philosophical questions about the physical nature of electromagneticfields to the computational requirements for real-world problem solving. My ambi-tion was to teach electromagnetics in a way that would engage not only the analyt-ical faculties of the brain but also its powerful processing abilities associated withvisual perception and intuitive integration of physical and mathematical relation-ships, abilities that are essential for innovation and the creative process.

One fundamental aspect that I had never considered seriously was the nature andrelationship of the electric and the magnetic fields. Yet, this became a key questionwhen I began teaching electromagnetics. Consider for example two identical posi-tive charges moving side by side at a constant velocity v, as shown in Fig. 12. Weknow that they are subject to a repulsive electric force Fe. However, they also expe-rience an attractive magnetic force Fm since moving charges represent an equivalentlocal current i, and parallel currents attract each other. Which force is greater?

In Search of the Intangible 11

Fig. 12 Forces between twomoving charges

Fig. 13 Classical electromagnetic analysis of moving charges

We can, of course, answer this question correctly with classical field theory. Letus use a slightly different configuration, shown in Fig. 13, that leads us to the answermore easily. We, as observers in the reference frame at rest, look at a line of equidis-tant charges that move at constant velocity v. A single charge q moves along withthe line of charges at the distance r. We can define a linear charge density λ (thenumber of positive charges per unit length) and an equivalent current I = λv. Theelectric force Fe acting upon the single charge will then be, according to Coulombslaw for line charges:

Fe = qE = qλ

2πεr(1)

For the magnetic force Fm we find

Fm = q(→v ×

→B)

= −qvμI

2πr= −qv

μελv2πεr

= −qλ

2πεrv2

c2 (2)

where we have introduced the velocity of light as c = (με)−0.5. We see immediatelythat these two opposing forces are proportional to each other, and that the magneticforce is always much smaller than the electric force for all realistic velocities v. Thenet force

Ft = Fe +Fm = qλ

2πεr

(1− v2

c2

)(3)