Springer advances in microwave and rf processing m willert porada (ed) (springer 2006) ww

Advances in Microwave and Radio Frequency Processing


Monika Willert-Porada (Ed.)

Advances in Microwave
and Radio Frequency Processing
Report from the 8th International Conference
on Microwave and High Frequency Heating
held in Bayreuth, Germany, September 3 – 7, 2001
With 469 Figures

*

P

E

*

*
M

R

*

E * A

*

Professor Dr. M. Willert-Porada
Chair of Materials Processing
University of Bayreuth
Universitätsstraße 30
D-95447 Bayreuth
Germany

Library of Congress Control Number: 2005934302
ISBN-10
ISBN-13

3-540-43252-3 Springer-Verlag Berlin Heidelberg New York
978-3-540-43252-4 Springer-Verlag Berlin Heidelberg New York

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is
concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,
broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication
of this publication or parts thereof is permitted only under the provisions of the German Copyright
Law of September 9, 1965, in its current version, and permission for use must always be obtained
from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law.
Springer-Verlag is a part of Springer Science+Business Media
springer.com
© Springer-Verlag Berlin Heidelberg 2006
Printed in the Netherlands
The use of general descriptive names, registered names, trademarks, etc. in this publication does not
imply, even in the absence of a specific statement, that such names are exempt from the relevant
protective laws and regulations and therefore free for general use.

Production: SPI Publisher Services

Typesetting: SPI Publisher Services
Cover Design: E. Kirchner, Heidelberg
Printed on add free paper

SPIN 10850172

30/3100/SPI - 5 4 3 2 1 0


Preface
Prometheus brought fire to mankind
Arthur R. von Hippel “Dielectrics and Waves”, 1954
Our contribution?
There are only few areas of research and development of a comparable scientific
and technological extension as microwave and high frequency processing. “Processing” means not only application of radiation of 300 MHz to 300 GHz frequency to synthesis, heating or ionisation of matter but also generation, transmission and detection of microwave and radio frequency radiation.
Microwave and high frequency sources positioned in the orbit are the foundation of modern satellite telecommunication systems, gyrotron tubes being presently developed in different countries all over the world will most probably be the
major devices to open up a new era of energy supply to mankind be means of fusion plasma. Although initiated by military purposes during the Second World
War (RADAR, Radio Detection and Ranging), microwave and high frequency
utilisation has spread over almost every important aspect of normal day life since
than, from individual mobile phones and kitchen microwave ovens to industrial
food processing, production of composites as sustainable building materials, green
chemistry, medical applications and finally infrastructure installations like GPS
and Galileo, to name only few examples.
These different areas of microwave and high frequency radiation application
can not be unified within one group of scientists and technologists. There are several distinguished communities active e.g., in the area of telecommunication systems, strong microwaves for fusion plasma or plasma based materials processing.
Research to improve fundamental knowledge leading to new non-military applications of high frequency technology, to support necessary regulations and to provide long term development of commodity and industrial applications as well as to
improve the knowledge about these new technologies within the society is less
well covered by scientific or professional organizations. In order to close this gap
and provide a forum for fruitful discussions a group of researchers from academia
and industry started to organize Microwave and High Frequency Heating Conferences in 1986, which take place every 2 years in a different European country. In

1993 AMPERE, Association for Microwave Power in Europe for Research and
Education (www.ampereeeurope.org) was established and the conferences were
organized on behalf of AMPERE since than. In addition to the regular conference
schedule Microwaves in Chemistry meetings were added 1998 and 2000.
Conference activities in the field of microwave and RF-applications show a remarkable growth: up to mid-80 of the 20th century IMPI (International Microwave
Power Institute, USA) almost exclusively covered the organized activities in the
field. The widespread availability of kitchen microwave ovens as well as the development of powerful microwave sources within national fusion programmes fa-


VI

Preface

cilitated use of this “cold” radiation for chemical syntheses and materials processing, with often quite unexpected results. Therefore professional organizations
like e.g., the American Ceramic Society and the Materials Research Society established Microwave Symposia within their regular conferences in the period
1988-1996. Numerous Symposia Proceedings volumes came out of theses conferences (e.g., MRS Proc. Vol. 124, 189, 269, 347, 430 and Ceram. Trans. Vol. 21,
36, 59, 80), including publications from the 1st and 2nd World Congress on Microwave and Radio Frequency Processing. New professional associations enter the
scene, like e.g., the Microwave Working Group in the USA, and different Societies in Japan and China.
The overview and technical papers contained in this book reflect the major areas
of activity not only of AMPERE members but also of a representative group of
other researchers worldwide. The topics were selected from contributions of the
8th International Conference on Microwave and High Frequency Heating, organised by AMPERE and held in September 2001 in Bayreuth, Germany. The papers
were referred by major specialists in the respective field.
The book is intended to provide non-specialists an overview of the State of the
Art in the field of microwave and high frequency hardware, measurement and
modelling as well as to give the specialists insight into the most advanced R&D
topics of microwave and high frequency radiation application in different disciplines.
Many experts and colleagues contributed to this book. I am particularly indebted to (in alphabetical order):
J.P. Bernard, France; J. Binner, UK; J. Booske, USA; S. Bradshaw, South Africa; A. Breccia, Italy; M. Brito, Japan; J.M. Catalá -Civera, Spain; T. Gerdes,
Germany; J. Gerling, USA; W. Jansen, Netherlands; W. Van Loock, Belgium; R.

Metaxas, UK; A. Mavretic, USA; T. Ohlsson, Sweden; P. Püschner, Germany; E.
de los Reyes, Spain; A. Rosin, Germany; G. Roussy, France; A. Schmidt, Germany; V. Semenov, Russia; M. Thumm, Germany; N. Tran, Australia.
My deep thanks go to the authors for their patience and effort to collect excellent papers; to colleagues for valuable suggestions and to my co-workers for many
hours of work to fit the individual contributions into a book.
Hopefully this book will facilitate further development of the fascinating field of
microwave and high frequency processing, in a synergetic effort of many groups
all over the world.

Monika Willert-Porada, Editor
Bayreuth, first half of the first decade of the 21st century


Contents
PART I: HARDWARE
UNDERSTANDING MICROWAVE HEATING SYSTEMS: A PERSPECTIVE ON
STATE-OF-THE-ART .................................................................................................3
H. C. Reader
MILLIMETER-WAVE-SOURCES DEVELOPMENT: PRESENT AND FUTURE.................15
Manfred Thumm and Lambert Feher
3.5 KW 24 GHZ COMPACT GYROTRON SYSTEM FOR MICROWAVE
PROCESSING OF MATERIALS ..................................................................................24
Yu. Bykov, G. Denisov, A. Eremeev, M. Glyavin, V. Holoptsev,
I. Plotnikov, V. Pavlov
DESIGN GUIDELINES FOR APPLICATORS USED IN THE MICROWAVE
HEATING OF HIGH LOSSES MATERIALS..................................................................31
Juan V. Balbastre, E. de los Reyes, M. C. Nuño and P. Plaza
DESIGN PARAMETERS OF MULTIPLE REACTIVE CHOKES FOR OPEN
PORTS IN MICROWAVE HEATING SYSTEMS ............................................................39
J. M. Catalá-Civera, P. Soto, V.E. Boria, J. V. Balbastre and
E. de los Reyes

MICROWAVE HIGH-POWER FOUR POST AUTO-MATCHING SYSTEM ......................48
Pedro Plaza, Antoni J. Canós, Felipe L. Penaranda-Foix and
Elias de los Reyes
DESIGN OF AN APPLICATOR FOR PROCESSING OF NANOSCALE
ZEOLITE/POLYMER COMPOSITES WITH SUPERPOSED STATIC MAGNETIC
FIELD .....................................................................................................................56
Ralph Schertlen, Stefan Bossmann, Werner Wiesbeck

PART II: MEASUREMENT TECHNIQUES AND REGULATIONS
MEASUREMENT TECHNIQUES FOR MICROWAVE AND RF PROCESSING ..................65
Georges Roussy
DIELECTRIC CHARACTERISATION OF HIGH LOSS AND LOW LOSS
MATERIALS AT 2450 MHZ .....................................................................................77
Andrew Y.J Lee and V. Nguyen Tran
EUROPEAN REGULATIONS, SAFETY ISSUES IN RF AND MICROWAVE
POWER ...................................................................................................................85
Walter Van Loock


VIII

Contents

FUTURE PROSPERITY OF INDUSTRIAL, SCIENTIFIC AND MEDICAL (ISM)
APPLICATIONS OF MICROWAVES ...........................................................................92
David Sánchez-Hernández and José M. Catalá-Civera
ELECTRIC FIELD MEASUREMENTS FOR COMMERCIALLY-AVAILABLE
MOBILE PHONES ..................................................................................................103
Antonio Martínez-González, Ángel Fernández-Pascual and
David Sánchez-Hernández

USE OF THE DIELECTRIC PROPERTIES TO DETECT PROTEIN
DENATURATION ...................................................................................................107
S. A. Barringer and C. Bircan
SANDALWOOD MICROWAVE CHARACTERISATION AND OIL EXTRACTION ...........119
V. Nguyen Tran
DIELECTRIC SPECTROSCOPY AND PRINCIPAL COMPONENT ANALYSIS AS
A METHOD FOR OIL FRACTION DETERMINATION IN OIL-IN-WATEREMULSIONS WITH VARYING SALT CONTENT........................................................129
M. Regier, X. Yu, S. Ghio, T. Danner, H. Schubert
MICROWAVE NON-DESTRUCTIVE EVALUATION OF MOISTURE CONTENT
IN LIQUID COMPOSITES IN A CYLINDRICAL CAVITY AT A SINGLE
FREQUENCY .........................................................................................................138
J. M. Catalá-Civera, A. J. Canós, F. Peñaranda-Foix and E. de
los Reyes
MILLIMETER WAVE SPECTROSCOPY OF ALUMINA-ZIRCONIA SYSTEM ................149
Saburo Sano, Akihiro Tsuzuki, Kiichi Oda, Toshiyuki Ueno,
Yukio Makino and Shoji Miyake
A MODIFIED CAVITY PERTURBATION TECHNIQUE FOR MEASUREMENT
OF THE DIELECTRIC CONSTANT OF HIGH PERMITTIVITY MATERIALS. .................155
Sheila Oree
PART III: MODELLING
FINITE ELEMENTS IN THE SIMULATION OF DIELECTRIC HEATING
SYSTEMS ..............................................................................................................167
G.E Georghiou, R.A Ehlers, A. Hallac, H. Malan, A.P.
Papadakis and A.C. Metaxas
EXAMINATION OF CONTEMPORARY ELECTROMAGNETIC SOFTWARE
CAPABLE OF MODELING PROBLEMS OF MICROWAVE HEATING ...........................178
Vadim V. Yakovlev
A HYBRID APPROACH FOR RESOLVING THE ELECTROMAGNETIC FIELDS
INSIDE A WAVEGUIDE LOADED WITH A LOSSY MEDIUM .....................................191
Viktor Vegh, Ian W. Turner

Contents

IX

A NOVEL FDTD SYSTEM FOR MICROWAVE HEATING AND THAWING
ANALYSIS WITH AUTOMATIC TIME-VARIATION OF ENTHALPYDEPENDENT MEDIA PARAMETERS .......................................................................199
Malgorzata Celuch-Marcysiak, Wojciech K.Gwarek,
Macie Sypniewski
SIMULATION OF MICROWAVE SINTERING WITH ADVANCED SINTERING
MODELS ...............................................................................................................210
Hermann Riedel, Jiri Svoboda
FINITE ELEMENT MODELLING OF THIN METALLIC FILMS FOR
MICROWAVE HEATING .........................................................................................217
R.A. Ehlers and A.C. Metaxas
ANALYSIS OF COUPLED ELECTROMAGNETIC AND THERMAL MODELING
OF PRESSURE-AIDED MICROWAVE CURING PROCESSES ......................................226
J. M. Catalá-Civera, J. Monzó-Cabrera, A. J. Canós, F. L.
Peñaranda-Foix
SELECTIVE HEATING AND MOISTURE LEVELLING IN MICROWAVEASSISTED DRYING OF LAMINAR MATERIALS: AN EXPLICIT MODEL ....................234
J. Monzó-Cabrera, A. Díaz-Morcillo, J. M. Catalá-Civera,
E. de los Reyes
MICROWAVE HEATING OF READY MEALS – FDTD SIMULATION TOOLS
FOR IMPROVING THE HEATING UNIFORMITY ........................................................243
B. Wäppling-Raaholt, P. O. Risman and T. Ohlsson
PART IV: FOOD PROCESSING AND ENVIRONMENTAL
ENGINEERING APPLICATIONS
NOVEL AND TRADITIONAL MICROWAVE APPLICATIONS IN THE FOOD
INDUSTRY ............................................................................................................259

H. Schubert and M. Regie
MICROWAVE DRYING: PROCESS ENGINEERING ASPECTS ....................................271
SM Bradshaw
QUALITY OF MICROWAVE HEATED MULTICOMPONENT PREPARED
FOODS ..................................................................................................................282
Suvi Ryynänen
SENSORY EVALUATION OF DRIED BANANAS OBTAINED FROM AIR
DEHYDRATION ASSISTED BY MICROWAVES.........................................................289
Sousa, W.A.; Pitombo, R.N.M.; Da Silva, M.A.A.P.;
Marsaioli, Jr., A.
MICROWAVE METHOD FOR INCREASING THE PERMEABILITY OF WOOD
AND ITS APPLICATIONS ........................................................................................303
G. Torgovnikov and P. Vinden


X

Contents

SELECTIVE HEATING OF DIFFERENT GRAIN PARTS OF WHEAT BY
MICROWAVE ENERGY ..........................................................................................312
E. Pallai-Varsányi; M.Neményi; A.J.Kovács; E.Szijjártó
MICROWAVE IN SITU REMEDIATION OF SOILS POLLUTED BY VOLATILE
HYDROCARBONS ..................................................................................................321
D.Acierno, A.A.Barba, M.d'Amore ,V.Fiumara, I.M.Pinto,
A.Scaglione
BIO-DIELECTRIC SOIL DECONTAMINATION ..........................................................329
J.P.M. Janssen-Mommen, W.J.L. Jansen
WASTE TREATMENT UNDER MICROWAVE IRRADIATION .....................................341
A. Corradi, L. Lusvarghi, M. R. Rivasi, C. Siligardi, P. Veronesi,

G. Marucci, M. Annibali, G. Ragazzo
ENVIRONMENTAL ASPECTS OF MICROWAVE HEATING IN
POLYELECTROLYTE SYNTHESIS ...........................................................................349
E. Mateescu, G. Craciun, D. Martin, D. Ighigeanu, M. Radoiu,
I. Calinescu and H. Iovu
PART V: MICROWAVE APPLICATIONS IN CHEMISTRY
ROLE OF MICROWAVE RADIATION ON RADIOPHARMACEUTICALS
PREPARATIONS.....................................................................................................359
Enrico Gattavecchia, Elida Ferri, Biagio Esposito,
Alberto Breccia
FAST SYNTHESIS OF BIODIESEL FROM TRIGLYCERIDES IN PRESENCE OF
MICROWAVES ......................................................................................................370
C. Mazzocchia, A. Kaddouri, G. Modica, R. Nannicini
ALTERATION OF ESTERIFICATION KINETICS UNDER MICROWAVE
IRRADIATION........................................................................................................377
L. A. Jermolovicius, B. Schneiderman and J. T. Senise
MULTISTEP MICROWAVE-ASSISTED SOLVENT-FREE ORGANIC
REACTIONS: SYNTHESIS OF 1,6-DISUBSTITUTED-4-OXO-1,4-DIHYDROPYRIDINE-3-CARBOXYLIC ACID BENZYL ESTERS ................................................386
Mauro Panunzio, Maria Antonietta Lentini, Eileen Campana,
Giorgio Martelli, Paola Vicennati
RECENT APPLICATIONS OF MICROWAVE POWER FOR APPLIED ORGANIC
CHEMISTRY ..........................................................................................................390
Bernd Ondruschka and Matthias Nüchter
LIQUID PHASE CATALYTIC HYDRODECHLORINATION OF
CHLOROBENZENE UNDER MICROWAVE IRRADIATION .........................................398
Marilena T. Radoiu, Ioan Calinescu, Diana I. Martin,
Rodica Calinescu


Contents

XI

CONVENTIONAL AND NEW SOLVENT SYSTEMS FOR MICROWAVE
CHEMISTRY ..........................................................................................................405
Jens Hoffmann, Antje Tied, Matthias Nüchter and
Bernd Ondruschka
PART VI: INDUSTRIAL MICROWAVE APPLICATIONS
STATE OF THE ART OF MICROWAVE APPLICATIONS IN THE FOOD
INDUSTRY IN THE USA.........................................................................................417
Robert F. Schiffmann
MICROWAVE VACUUM DRYING IN THE FOOD PROCESSING INDUSTRY ................426
G. Ahrens, H. Kriszio, G. Langer
DEVELOPMENT OF AN INDUSTRIAL SOLID PHASE POLYMERIZATION
PROCESS USING FIFTY-OHM RADIO FREQUENCY TECHNOLOGY..........................436
Joseph W. Cresko, L. Myles Phipps, Anton Mavretic
RF WORLD TOUR .................................................................................................445
Jean-Paul Bernard
PART VII: FUNDAMENTALS OF MICROWAVE APPLICATION TO
MATERIALS PROCESSING
HOW THE COUPLING OF MICROWAVE AND RF ENERGY IN MATERIALS
CAN AFFECT SOLID STATE CHARGE AND MASS TRANSPORT AND RESULT
IN UNIQUE PROCESSING EFFECTS .........................................................................461
John H. Booske and Reid F. Cooper
ENHANCED MASS AND CHARGE TRANSFER IN SOLIDS EXPOSED TO
MICROWAVE FIELDS ............................................................................................472
V.E. Semenov, K.I. Rybakov
THERMAL RUNAWAY AND HOT SPOTS UNDER CONTROLLED
MICROWAVE HEATING .........................................................................................482
V.E. Semenov, N.A. Zharova

DENSIFICATION AND DIFFUSION PROCESSES IN THE BA,SR-TITANATE
SYSTEM UNDER MICROWAVE SINTERING ............................................................491
O.I. Getman, V.V. Panichkina, V.V. Skorokhod,
E.A. Shevchenko, V.V. Holoptsev
OBSERVATION OF THE MICROWAVE EFFECT ON THE DIFFUSION
BEHAVIOR IN 28 GHZ MILLIMETER-WAVE SINTERED ALUMINA .........................498
Toshiyuki UENO, Yukio MAKINO and Shoji MIYAKE, Saburo
SANO
DILATOMETER MEASUREMENTS IN A MM-WAVE OVEN .......................................506
G. Link, S. Rhee, M. Thumm


XII

Contents

IN SITU DETERMINATION OF SHRINKAGE UNDER MICROWAVE
CONDITIONS .........................................................................................................514
J. Bossert, C. Ludwig, J.R. Opfermann
MULTISTABLE BEHAVIOUR IN MICROWAVE HEATING OF CERAMICS ..................521
J. R. Thomas, Jr., Xiaofeng Wu, W. A. Davis
PART VIII: MICROWAVE SINTERING OF CERAMICS AND METALS
MICROWAVE SINTERING OF SILICON NITRIDE CERAMICS ....................................533
Kiyoshi Hirao, Mark I. Jones, Manuel E. Brito and M. Toriyama
NOVEL MATERIALS PROCESSING BY MILLIMETER-WAVE RADIATION PRESENT AND FUTURE .........................................................................................541
Shoji Miyake
CORRELATION BETWEEN DENSIFICATION AND E - PHASE FORMATION AT
MICROWAVE SINTERING OF SI3N4 CERAMICS ......................................................553
O. I. Getman, V. V. Panichkina, V. V. Skorokhod, I. V. Plotnikov,
V. V. Holoptsev

SINTERING BEHAVIOUR AND MECHANICAL PROPERTIES OF MICROWAVE
SINTERED SILICON NITRIDE .................................................................................562
Mark I Jones, Maria-Cecilia Valecillos, Kiyoshi Hirao, Manuel
E. Brito, Motohiro Toriyama
MILLIMETER-WAVE SINTERING OF HIGH PURE ALUMINA –
MICROSTRUCTURE AND MECHANICAL PROPERTIES .............................................570
Yukio Makino, Shoji Miyake, Saburo Sano, Hidenori Saito,
Bunkei Kyoh, Hideki Kuwahara and Akinobu Yoshikawa
MICROWAVE SINTERING OF LARGE-SIZE CERAMIC WORKPIECES .......................577
S. V. Egorov, N. A. Zharova, Yu. V. Bykov, V. E. Semenov
MICROWAVE ASSISTED SINTERING OF AL2O3 ......................................................583
S. Leparoux, G. Walter; Th. Lampke, B. Wielage
ABSORPTION OF MILLIMETER WAVES IN COMPOSITE METAL-CERAMIC
MATERIALS ..........................................................................................................591
A. G. Eremeev, I. V. Plotnikov, V. V. Holoptsev, K. I. Rybakov,
A. I. Rachkovskii
MICROWAVE SINTERING OF PM STEELS ..............................................................598
F. Petzoldt, B. Scholz, H. S. Park, M. Willert-Porada
FORMATION OF FUNCTIONALLY GRADED CEMENTED CARBIDES BY
MICROWAVE ASSISTED SINTERING IN REACTIVE ATMOSPHERES ........................609
R. Tap, M. Willert-Porada, K. Rödiger, R. Klupsch


Contents

XIII

PART IX: SYNTHESIS AND MICROWAVE PROCESSING OF
POWDERS
MICROWAVE PLASMA SYNTHESIS OF CERAMIC POWDERS ...................................619

Dieter Vollath, D. Vinga Szabó
MICROWAVE AND CONVENTIONAL HYDROTHERMAL SYNTHESIS OF
ZIRCONIA DOPED POWDERS .................................................................................627
F. Bondioli, C. Leonelli, C. Siligardi, G.C. Pellacani,
S. Komarneni
MICROWAVE DECOMPOSITION OF METAL ALKOXIDES TO NANOPOROUS
METAL OXIDES – A MECHANISTIC STUDY ..........................................................633
F. Bauer, T. Schubert, M. Willert-Porada
CHARACTERIZATION OF SIC PRODUCED BY MICROWAVES ..................................645
Juan Aguilar, Zarel Valdez, Ubaldo Ortiz, Javier Rodríguez
MICROWAVE ASSISTED SYNTHESIS OF CATALYST MATERIALS FOR PEM
FUEL CELLS .........................................................................................................651
T. Schubert, M. Willert-Porada
EXCITATION OF SODIUM IN POWDERLIKE SILICATES BY MICROWAVE
HEATING ..............................................................................................................661
M. Hasznos-Nezdei, E. Pallai-Varsányi, L. P. Szabó and S Szabó
PART X: NEW APPLICATIONS AND PROCESSES RELATED TO
MICROWAVE AND RF HEATING
RF AND MICROWAVE RAPID MAGNETIC INDUCTION HEATING OF
SILICON WAFERS .................................................................................................673
Keith Thompson, John Booske, Yogesh Gianchandani,
Reid Cooper
INDUSTRIAL HIGHER FREQUENCY MICROWAVE PROCESSING OF
COMPOSITE MATERIALS.......................................................................................681
Lambert Feher and Manfred Thumm
DRILLING INTO HARD NON-CONDUCTIVE MATERIALS BY LOCALIZED
MICROWAVE RADIATION .....................................................................................687
E. Jerby and V. Dikhtyar
DESIGN OF AVIONIC MICROWAVE DE-/ANTI-ICING SYSTEMS .............................695
Lambert Feher and Manfred Thumm

APPLICATION OF MICROWAVE TO GLAZE AND CERAMIC INDUSTRY ....................703
C. Leonelli, C. Siligardi, P. Veronesi, A. Corradi
MICROWAVE ASSISTED BINDER BURNOUT ..........................................................710
J.Grosse-Berg, M. Willert-Porada, L. Eusterbrock, G.Ziegler


XIV

Contents

CVD-PROCESSES IN MICROWAVE HEATED FLUIDIZED BED REACTORS .............720
T. Gerdes , R. Tap, P. Bahke , M. Willert-Porada
PROCESSING OF CARBON-FIBER REINFORCED COMPOSITE (CFRP)
MATERIALS WITH INNOVATIVE MILLIMETER-WAVE TECHNOLOGY ....................735
Christian Hunyar, Lambert Feher and Manfred Thumm
BASIC RESEARCH AND INDUSTRIAL PRODUCTION USING THE SPARK
PLASMA SYSTEM (SPS) .......................................................................................745
Mamoru Omori
COMBINED PROCESSES: LASER ASSISTED MICROWAVE PROCESSING AND
SINTERCOATING ...................................................................................................755
M. Willert-Porada, T. Gerdes, Ch. Gerk, H.S. Park

AUTHOR INDEX .............................................................................................769
SUBJECT INDEX .............................................................................................773


Understanding Microwave Heating Systems:
A Perspective on State-of-the-Art
H. C. Reader
Department of Electrical and Electronic Engineering, University of Stellenbosch,

Private Bag X1, 7602, South Africa

Introduction
An interesting picture emerges when published literature on state-of-the-art in microwave heating is studied over the last five-year period. A search using engines
such as ScienceDirect and ISI Web of Science finds only 4 such papers bold
enough to make the claim. The two papers relevant to the present discussion,
[1, 2], reveal opposite extremes. [1] reviews research on high power microwave
sources, some of which can be regarded as exotic. [2] examines microwave heating of milk, using a domestic oven, where concerns focus on milk proteins, enzymes, vitamins, micro-organisms and hazardous over-heating. Interestingly, researchers seem reluctant to make dramatic claims in terms of applicator design,
computational methods, control methods and combinational sources of energy. If
the search is broadened to “state-of-the-art in heating”, 61 papers are found of
which 3 are relevant. It would seem that workers in our discipline become bolder
if “state-of-the-art” is softened to novel. 66 papers can be found containing the
words novel and microwave and heating.
What are the reasons for this? One simple answer is that perspectives on how
people regard state-of-the-art vary considerably. Another is that manufacturers,
who for obvious commercial reasons need to emphasise high-tech features, do not
publish freely in academic literature. A more detailed analysis is likely to reveal
that general researchers making use of microwave heating are uncertain as to what
“state-of-the-art” might be. Novel, on the other hand, suggests incremental improvements with particular features coming to the fore. It may also be found that
after the initial introduction of commercial microwave ovens in the late 1940's [3],
and after our understanding of applicator and source physics fundamentals reached
a certain level, little room exists for significant developments.
A more specific technical survey can be obtained from members’ millennium
statements appearing in the Ampere Newsletters of January and April 2000. A
sample of hopes and predictions include:


4

Reader

x using RF 50 Ohm technology (no adjustments necessary for different load conditions)
x converting long-standing laboratory research into industrial applications
x developing on-line process validation tools with non-invasive sensors
x using microwave developments to improve the quality of our environment
x developing numerical and optimization methods with attention to the userinterface
x accepting that microwave applicators have reached maturity - use them as they
are!
Further insights on the matter are derived from feedback in the Ampere April
2000 letter on the 7th International Conference on Microwave and High Frequency
Heating where delegates ask for more on food and industrial applications,
EMC/EMI and health, medical applications, modelling relevance, measurement
techniques, optimisation and control tasks, and microwave sources.
A direct question on “state-of-the-art” to a wide variety of active workers [4] in
the field elicits the following responses:
x Bernard Krieger declares: “in my opinion the best applicator is the simplest applicator and the best overall system is a hybrid system that uses the minimum
amount of microwave energy and the maximum amount of conventional heating”. Krieger adds further that customers are often subtly presented with the
weaknesses of microwave units (this applicator DOES deal with nonuniformity!) and not their strengths.
x R F (Bob) Schiffmann, after 40 years of experience, finds that in most cases
applicators have been multimode cavities - big boxes. The reason? For successful processes the load has to be quite lossy; in such cases the multimode cavities are cheap, easy to build, forgiving to variations in the load and provide
good enough coupling efficiency. He argues, for a variety of reasons, that
where loads have low loss the likelihood of commercial success is small.
Schiffmann [5] reviews the spectacularly poor predictions on the success of
domestic microwave ovens and criteria for successful microwave systems (eg.
product cannot be produced any other way). He also considers barriers, one of
which is the lack of understanding of microwave heating and unrealistic expectations of what can be done.
x A C (Ricky) Metaxas suggests that the specific application one is considering
determines whether RF or microwave, and which type of applicator, is selected.
If it is large, planar, broadloom material requiring drying, then a balanced or
stray-field applicator at RF is the answer. If, on the other hand, it is a small liquid one is processing, then a TM010 applicator, etc.

x R V (Bob) Decareau applied lateral thought to the question and raised the consideration of harnessing power gathered in space (solar space power, or SPS),
international space stations, space agriculture and microwave freeze drying in
space. J M (John) Osepchuk touched upon this theme in a JMPEE guest editorial in 1998 (Vol 33 (3)) entitled “Predictions and Breakthroughs”, where he
stated that there has not been a major breakthrough in the field of microwave
power since the microwave oven of the 1960s. The editorial offers “candidate


Understanding Microwave Heating Systems

5

breakthroughs” which include microwave lighting, SPS (it appears that Japan
has committed to developing an SPS before 2040 [4]), a new microwave power
source (solid-state [4]), and a microwave clothes dryer.
With all the preceding material as quite contrasting background, what criteria
could be applied reasonably to define a high frequency heating system to be stateof-the-art? To explore this question, some general characteristics should be
sketched.

EM Properties of High Frequency Heating Systems
This paper is concerned with microwave heating systems, but it is most important
to emphasise that these frequencies are not always the sensible choice for this
class of heating. Consideration must be given to frequencies in other ISM (industrial, scientific and medical) allocated bands, which can be found between
6.78 MHz and 245 GHz [6]. Some of these bands are narrow and others relatively
broad. Metaxas and Meredith [7] define the microwave band between 300 MHz
and 30 GHz (representing wavelengths of 1 m and 0.01 m respectively). Osepchuk
[4] suggests an alternative where microwaves for heating refer to any source
wavelength with similar dimensions to the object of interest. The latter highlights
the distinction between quasi-static or dynamic system properties. Roughly
speaking, if an applicator is a tenth of a wavelength or smaller than the source
wavelength, quasi-static conditions hold. Electric and magnetic fields can then be

thought of separately. If the applicator is larger, electromagnetic variations will
become evident. For practical purposes the definition in [7] is used here. In the
microwave band where an applicator has a dimension of the order of 0.5 m, field,
current and heating nonuniformity must be considered. The two most commonly
used microwave heating frequencies are around 915 MHz and 2.45 GHz. Excellent accounts of these microwave heating frequencies, with historical background,
are given by Osepchuk [3] and Thuéry [8].
The lower end of the ISM bands, which includes frequencies of 6.78 MHz,
13.56 MHz, 27.120 MHz and 40.68 MHz (wavelengths of 44.2 m down to
7.37 m), is spoken of as the RF band. Apart from dimensional aspects, power absorption, arcing and energy penetration into an object are pertinent issues. In
chapter 2 of [9] and elsewhere it is shown that the power absorbed per unit volume
(power loss density) is proportional to the frequency and to the square of the electric field (E-field). This remark must be qualified. Assumptions are that: 1) load
dielectric properties do not change with frequency and processing conditions; 2)
frequencies are above those where ionic conduction dominates. Water’s dielectric
properties, for example, change significantly with frequency. At microwave frequencies, where the assumptions are reasonable for illustrative purposes, to
achieve the same absorbed power, a twenty-five-fold increase in the source frequency would lead to a five-fold decrease in the E-field strength. As breakdown in
air is seen at a value of 30 kV/cm, at standard temperature and pressure (STP), any
lowering in field strength reduces arcing problems. The breakdown level is af-


6

Reader

fected by load dielectric conditions and would also occur at a lower E-field values
if pressure is reduced; vacuum is sometimes preferred for various processes. From
this perspective, higher microwave frequencies may be better. Higher frequencies
also promote heating uniformity in multimode applicators. Energy penetration into
a product, however, is inversely proportion to frequency. The same twenty-fivefold increase frequency would lead to a five-fold decrease in penetration depth.
Before proceeding with microwave applicators alone, the discussion should be
balanced with a consideration of RF and microwave frequency, or high frequency

(HF), heating systems generally. Material displacement currents (dipolar polarisation) and conductive currents occur; conductive currents usually dominate at RF
and displacement currents at microwave frequencies. RF heating is loosely associated with drying (textiles, fibre-glass bales, paper and board), heating and welding; microwave heating with food processing (including tempering and defrosting), curing and drying [10]. The advantages of HF heating over purely
conventional approaches are widely described. Thuéry [8] and Roussy and Pearce
[11] cite rapid heating, volumetric deposition of energy, economy of energy due to
specific heat deposition, space and human resource savings, reduced pollution,
ease of application, instantaneous on and off operation, adaptation to existing operations, possible product quality improvement, and automation possibilities.
In the field of drying, Metaxas [10], discusses mechanisms and makes the point
that purely HF drying applications are unlikely. This is best illustrated in Figure 1.
The dimensions of the object or volume to be treated, and load thermal and electrical properties, are significant factors in applicator design. The frequency choice
is influenced by the total required power. Microwaves are commonly employed at
low powers (1 - 20 kW). Higher powers (> 200 kW) usually make use of RF. In
the food industry, Schiffmann [4] indicates that several hundred microwave installations exist for tempering and bacon cooking that reach up to 500 kW. Finances must also be considered; however RF and microwave are remarkably
similar when considered en toto on a per watt basis [11].
In terms of RF generators, there are two classes [10, 11]: 1) Crystal controlled
frequency oscillators with power amplifiers. RF transmitter technology can be
used to generate large powers for industrial heating applications. This is channelled via a matching network (in coaxial cable of 50 Ohm) to the applicator or
load; 2) Power oscillators (class C) in which the load is a part of the tank resonant
circuit - variable matching is an implicit part of the design. The load greatly influences the operating frequency and high harmonic generation requires filters which
must be designed to allow for frequency drift. In regions, such as the US, where
the operating RF frequency may vary, the power oscillator is preferred as it is
much cheaper - it also achieves higher efficiencies. In Europe with electromagnetic compatibility (EMC) requirements it is usually necessary to use the first option.
In very broad terms, basic RF applicators include the through-field (eg. parallel
plate), the stray-field or fringe-field and variations thereof. Because of the wavelengths involved, these are very much quasi-static systems. Matching circuits are
required. The parallel plate suffers from E-fields normal to the upper workpiece
surface. In high loss materials, the air gap E-field must be high to obtain heating;


Understanding Microwave Heating Systems

7

Mean Moisture Content

arcing is then a consideration, requiring careful electrode design. Thin objects are
also difficult to heat. Stray-field and staggered though-field rods can be used both resulting in fields that are nearly parallel to load upper surface [11].

Constant
drying rate

Falling drying
rate
1. Conventional
2. HF only

2

Mc
3

4

3. Simultaneous
4. Sequential
combination
1
Time

Fig. 1. Moisture removal through conventional, HF and combinational systems (after [10])

Main Classes of Microwave Applicators and Sources

The focus now falls on microwave systems where there are three main classes of
applicator: travelling wave, near field (often lightly-resonant) and resonant.
Choice depends on the nature and dimensions of the material to be heated, subject
to constraints of matching, field uniformity, safety aspects, industrial factors, etc.
For high volume materials, the applicator is usually a multimode cavity whose
dimensions are large compared to those of the material and wavelength. For small
volume loads, energy coupling to an oversized cavity is particularly inefficient single mode cavities are used instead [8].
Travelling wave applicators make use of a matched waveguide which sustains a
propagating wave in a well-defined fundamental mode. Material is then judiciously inserted into sections of the guide so as to intercept the propagating energy. Sheet and filamentary materials are commonly heated in this way.
Near-field applicators can be open-ended waveguides, a variety of antennas, or
slotted waveguide feeds. They are found in the processing of rock ores at very
high power, through the heating of wood, foods etc., at medium power, right down
to the treatment of cancers by heat (hyperthermia, see [12], for example).
Resonant applicators, single or multimode, usually exist in rectangular and cylindrical form. Various polygonal shapes have been attempted, mainly with efforts
made to affect mode distributions. Single mode cavities are often required for


8

Reader

higher value, smaller volume products, where processing speed is not the main
variable. In general, for the same power applied, single mode resonant heaters will
establish much higher electric field strengths and thus power densities
(107 kW/m3) [7]. Under resonance, heating is very rapid. The multimode cavity is
used for bulkier items in batch or continuous processes - they are the “big boxes”
associated with Schiffmann earlier [4].
Whatever the intended purpose, the microwave heater has two essential components, an energy source and an applicator and then other system components, as
depicted in Figure 2. The principal concern of a batch multimode applicator is
heating uniformity. Computational studies and measurement can be helpful in this

regard. Given the theoretical possibility of the number of modes that can exist
within a cavity, it would be natural to expect more modes to exist within increasing dimension applicators. The theoretical possibility of modes existing and the
excitation of those modes should not be confused. Mode stirrers and randomises
improve heating non-uniformity in batch ovens, while in continuous or conveyorbelt multimode ovens, product movement accomplishes the same purpose.

Applicator
(e.g., waveguide, antenna,
multimode, single mode
or slotted feed cavities)
Conventional heating
(e.g., hot air, infrared)

Control

Circulator/
isolator/
matching

Microwave
source
and power
supply

Fig. 2. Generic microwave heating system blocks - not all may be present (after [9]).

In a single-mode applicator, concerns of heating uniformity are replaced with
interest in whether enough material can be processed. Analytical design is more
likely with this cavity. In single-mode circular waveguide geometries, the TM01p
(TM010 typically) are the most popular because of the coaxially placed load. TM11n
can deal with larger workloads because it has two eccentric heating locations.

When dealing with real loads, hybrid modes are established, and this should be
considered if careful design is attempted. Impedance matching (iris, automatic
stub tuners, etc) in single mode cavities is important. The most common rectangular equivalent form of this applicator is the TE01n. There are some interesting
variations reported: a spherical cavity for water droplet treatment; different
waveguide input angles for matching into cylindrical applicators; grooved rectangular cavity TE113 for fusing alumina or glass rods 30 mm diameter in 3 minutes;
cylindrical waveguide TM01 mode and internally divided into cavities by metal
disks (each disk is simply an iris) [8].
Near-field applicators, such as slotted waveguide feed, are often constructed for
conveyor-belt applications. They are designed to be weakly frequency dependent
and are thus fairly insensitive to slight changes in dielectric properties of the materials. This lowered dependency gives more freedom in the parameters associated


Understanding Microwave Heating Systems

9

with the load, but in units such as slotted feeds, this comes at a price - that of design complexity. In the slotted waveguide feed, the slot interrupts the normal current flow on the waveguide walls in a specific manner, yielding a chosen radiation
profile. The interslot spacing is forced by the wavelength of the source, but precise
slot position, with respect to an imaginary central line drawn along the wall, determines the radiation and ultimately load’s heating contours [9].
Understanding the field distribution and modal formations within applicator
classes can assist in their proper choice and usage. Examples can be found in [9]
and some of these will be discussed at the conference presentation.

Measurement and Design Methods
Power meters, diode detectors, multimeters, oscilloscopes, spectrum analyzers
(SAs), automatic network analyzers (ANAs), S-parameters, voltage standing wave
ratio (VSWR), field measurement and probing methods, material dielectric property determination (a significant field in its own right) and temperature measurement are all part of a basic toolbox available to people involved in microwave
heating. Neophytou and Metaxas [13] refer to the ANA as the single most important advance in recent years in the design of HF processing systems.
Roussy and Pearce [11] discuss microwave measurements broadly. Power
measurement is the most fundamental measurement and is accomplished by bolometers (thermally sensitive), diodes (power sensitive) or calorimetric methods.

Forward and reverse power, a sign of load energy absorption, is determined by a
directional coupler. Frequency measurements are made with frequency counters
and spectrum analysers. Field measurements are made with electric and magnetic
antennas (also can use optical devices). Several common and ingenious temperature measurement schemes are available and will not be pursued here.
The usage of SA’s, ANA’s, S-parameters (relatable to VSWR and impedance
parameters) and field evaluation is extensively examined in [9]. Application of
this knowledge, and practical, analytical and computational methods, forms the
basis of design. Attention will be given to this during the conference presentation
with pictorial support. Due to space restrictions, these illustrations will only be
available from the author on request.

Computational Tools and the Role They Should Play
In purely design terms, a widely published view is that simulation, combined with
experimental and analytical evaluation of microwave cavities, forms an integral
part of microwave heating studies. A defendable view is that most microwave
heating applications simply require a box with suitably applied microwave energy.
Computers can also be thought of on a wider front, for example in knowledgebased systems to aid design of system specification, or neural networks for on-line


10

Reader

process control. The following presents facets of what can be obtained through
computation and measurement.
In some applicators, single-mode being a good example, analytical expressions
can be processed to yield a good description of heating operation. In other cases,
analytical expressions are most awkward or even impossible to formulate, and
here simulation is an invaluable tool allowing users to see what is happening inside cavities [9]. Main published methods applied to this field are the finite element method (FEM) in the frequency (FEFD) and in the time domains (FETD),
the finite difference time domain method (FDTD), the transmission line matrix

method (TLM), the method of moments (MOM), and the method of lines (MOL).
Several pictorial examples of loaded and unloaded cavities can be found in [9]
which demonstrate the properties of analytical, computational (FEM) and measurements studies. Metaxas [10] provides a helpful summary of techniques applied
to microwave heating. Attention to validation of codes should always be given, as
it is not uncommon to obtain plausible but quite inaccurate results.
Groups such as the Institute for High Frequency Techniques and Electronics in
Karslruhe Germany eg. [14] and others are coupling electromagnetic and thermal
modelling within codes such as FDTD to simulate conventional, microwave and
combined heating. This is no mean task and will certainly make significant contributions to optimised systems as the research matures. An important requirement
will be knowledge of varying load dielectric properties with temperature.
Knowledge based systems (KBS) can be thought of as the use of databases and
specialist knowledge to emulate the thought process of an expert. An example
quoted [10] is EHEAT: A package which examines options available to customers
when considering applications which involve solely the use of HF. Apart from advising on the choice of equipment to be used, the package includes an economic
assessment based on a cost-benefit analysis which gives payback periods for the
various options.
On-line process control is, and will be, an area significantly affected by computers. The development of advanced sensors (for example giving reliable indications of either localised or volumetric moisture content in wood), coupled with sophisticated control techniques has much scope. In this regard, approaches such as
the use of neural networks, which can be trained, may be of assistance particularly
under nonlinear conditions. An interesting example of neural networks is the determination of full penetration in laser welding [10].

Comments on Safety and EMI/EMC, and Practical Matters
As this paper has an element of “state-of-the-art” the question of safety and electromagnetic interference (EMI) and EMC will be introduced with reference to related issues associated with SPS (solar space power), a concept first proposed in
1968 by Glaser (see [15]). In his well-referenced policy review article on the subject, Osepchuk [15] presents an account of electromagnetic energy safe usage and
interference and sketches the worldwide towards international harmonization of


Understanding Microwave Heating Systems

11

standards. Osepchuk stresses the need for international standard setting, which
must now be regarded as inevitable. In terms of safety, published recommendations in the microwave band mostly vary between 1 and 10 mW/cm2 and should
be checked by a competent body in any given application. In terms of interference,
the most recent out-of-band emission limits are found in the latest edition of
CISPR 11 (see [6]), which is the standard on ISM equipment generated by the
special committee under the auspices of the International Electrotechnical Commission (IEC). In safety and EMI/EMC terms, manufacturers and users of microwave heating equipment must expect to comply with more tightly defined legislation.
Apart from source harmonic content, conducted emissions, applicator unintentional leakage (for example through seams), the design of chokes at product entry
ports must enjoy specific attention. Vale, Meyer and Palmer [16, 17] have applied
some advanced computational and measurement techniques to this subject.
Shielding in general is an important constraint with financial implications.
Meredith [18] provides useful sections on procedures for testing high power installations and equipment safety, and on economics and specification of industrial
microwave equipment.
When industrialising equipment, choice of material bears consideration. For
applicator and waveguide walls, Metaxas and Meredith [7] suggest that for fairly
heavily loaded conditions (Q-factor < 100), non-magnetic stainless steel is an excellent material - hard and basically free of corrosion problems. For lightly loaded
conditions (Q-factor > 200), wall currents are such that stainless steel heats significantly. Materials of lower resistivity such as aluminium or copper should then
be considered. Thuéry [8] states that it is imperative that supports, conveyor-belts,
partitions, water seals, joints, etc., be made from very low loss dielectrics. The list
of acceptable materials is in fact very restricted: polyethylene, polypropylene,
polytetraflourethylene (PTFE, Teflon) and silicones [8]. Osepchuk [4] adds that
under some circumstances, for example elevated temperatures, materials such as
ULTE, polysulfone and composites, could be included.
Where localised high power density conditions prevail, electric arcing and corona discharges are possible. Vacuum conditions exacerbate the problem. Precautions include: sharp angles and metals objects are to be avoided, quarter-wave
traps can be used to reduce current to zero at critical points, soldered surfaces
must be smooth and the enclosure must be free of traces of iron filings or dust. Industrially, sources and applicators usually exist in hostile environments and may
need to be dust-proof, waterproof, resistant to corrosion by salt and acid, wide
variations in temperature, shocks, and vibrations. Safety cut-outs to guard against
mis-use are also needed [8].

State-of-the-Art and the “Best Applicator for the Job”

Intimated in the preceding discussion is that the physics governing the behaviour
of HF heating systems is really quite well understood and that no new dramatic


12

Reader

discoveries should be expected. This does not mean that new systems, through insightful and lateral application of thought, will not continually be found. Metaxas
suggests that a state-of-the-art system making use of an RF or microwave applicator would certainly be a hybrid system where hot air, steam or other conventional heat is used, pressure or vacuum control may be provided, a cooler device
may be used, and perhaps some kind of heat recovery process may be involved in
the input or output of the system [10]. Thuéry [8] cautions that microwaves do not
provide a universal solution, but should be considered whenever all other processes fail to solve an industrial problem - microwaves then become unique and offer considerable savings compared to other processes. Osepchuk and Decareau
predict quite new developments (section 1).
My own perspective is that there is scope within each element of the whole
system for state-of-the-art features to be advanced. By way of illustration, consider the blocks of Figure 2, beginning with the source. This was originally the
domain of tube devices. Thuéry [8] identifies that solid-state oscillators in microwave appliances has been the subject of a number of patents since the seventies.
The power outputs of silicon transistors are of the order of 100 W at 950 MHz and
15 W at 2.45 GHz. These powers are likely to double in the near future [8] and
should lead to an increase in the use of solid-state sources particularly in the medical and domestic applications. Power combiners could be used to obtain sufficient
source levels. The cellular phone industry requirements have driven many of the
developments in the field. This would fall directly in line with EMC trends requiring improved emission control and stability.
In terms of the applicator and control blocks, there are several developments
that are presently reported and that will continue to take place. Energy distribution
within the load can always be optimised through computational and empirical
study for a specific purpose. For the computational investigations, the determination of load constitutive properties as a function of temperature will need to be refined. With this knowledge, coupled electromagnetic and thermal codes will yield
valuable information for process control. The work at Karlsruhe [14] is an example. In addition to this knowledge, clever control methodologies can be applied.
One such method is the phase control method of Meier and de Swardt [19]
whereby low power injection locking of magnetrons permits energy deposition to
be actively moved through a load. Concerning overall system construction some

novel work has been published by Vale, Meyer and Palmer [16, 17] on optimised
choke design. Here mode cancellation principles and mode-matching analysis
combined with generic algorithms are employed. 2.45 GHz chokes have been built
and recently tested. This will be reported at the conference.
Modern developments also include available industrial combinational heating
such as the Microwave-Assisted Gas Firing (MAGF) unit reported by Bond [4],
where applications in the ceramics field, requiring roughly 15% of microwave
(896 MHz in industrial units) energy, result in faster throughputs, improved product quality and reduced flourine emissions. Krieger’s remark at the beginning of
this paper [4] adds weight to these combinational approaches, emphasizing the
minimum usage of microwave energy. Krieger provides further prudent counsel
[4] that the critical items are related to what the customer must live with, including


Understanding Microwave Heating Systems

13

issues such as: how well conveyor-belts track in the oven; ease of loading products; cleaning; dealing with condensation, dust, fumes and hot air re-circulation;
preventing fires and arcing (a tough issue). Schiffmann [5] examines criteria for
successful adoption of new microwave applications, barriers to their adoption and
improving the likelihood of success. His adage of “why microwaves?” rather than
“microwaves!” suggests a sensible starting point.
As to the question of “what is the best applicator for the job?”, academic interests of careful understanding of applicator behaviour must be offset with the industrial savoir-faire of the previous paragraph. Where microwaves can be demonstrated to provide unique advantages, trade-offs between product field profiles,
economics and quality must guide the designer.

Conclusion
It was suggested to me that more might be said by way of conclusion. This indeed
would be appropriate in a defined area of dielectric heating. My view is that in
some of these areas one best solution will be apparent and in others, several good
choices may be made. I have thus presented perspectives on the subject. We must

apply our minds appropriately, mindful of the physics and practicalities, to develop “state-of-the-art” microwave heating systems.

Acknowledgements
J Binner for first contacting me to suggest this paper, M Willert-Porada, A C
Metaxas (Ampere President) and J Binner for commenting on the paper’s development throughout, and J M Osepchuk, R V Decareau, R F Schiffmann, B
Krieger, J von Hagen, N Tran, John Zimmerly and M Bond for substantial inputs
and correspondence. Present and past colleagues and students in the Stellenbosch
Electro-Heat Group including J B de Swardt, S M Bradshaw, T V Chow Ting
Chan (co-author of recent book, [9]), J W Gerber, P Siebritz, I M Meier, M Rimbi,
E van Wyk; Colleagues in our EEM Group including J H Cloete, D B Davidson,
K D Palmer and P Meyer; Technical Colleagues W Croukamp, J C J Greyling, P
Kruger and U Buttner.

Literature
[1] S H Gold and G S Nusinovich, “Review of High-Power Microwave Source Research”,
Rev. Sci. Instrum, 68 (11), Nov. 1997, pp. 3945 - 3974.
[2] R Sieber, P Eberhard and P U Gallmann, “Heat Treatment of Milk in Domestic Microwave Ovens”, Int. Dairy Journal, 6 (3), Mar. 1996, pp. 231 - 246.


14

Reader

[3] J M Osepchuk, “A History of Microwave Heating Applications”, IEEE Trans. MTT,
32 (9), Sept. 1984, pp. 1200 - 1223.
[4] Private communications with: J Binner, M Bond, R V Decareau, B Krieger, A C
Metaxas, J M Osepchuk, R F Schiffmann, N Tran and M Willert-Porada.
[5] R F Schiffmann, “Microwave Processes for the Food Industry” in “Handbook of Microwave Technology for Food Applications” edited by A K Datta and R C Anantheswaran, Marcel Dekker, New York (2001).
[6] IEC CISPR 11, Industrial, Scientific and Medical (ISM) Radio-Frequency Equipment Electromagnetic Disturbance Characteristics - Limits and Methods of Measurement,
3rd edition, 1997, p. 13.

[7] A C Metaxas and R Meredith, "Industrial Microwave Heating", Peter Peregrinus Ltd.,
London, UK, ISBN: 0-906048-89-3, 1988.
[8] J Thuéry, edited by E H Grant, “MICROWAVES: Industrial, Scientific and Medical
Applications”, Artech House Publishers, Boston and London, ISBN: 0-89006-448-2,
1991.
[9] T V Chow Ting Chan and H C Reader, “Understanding Microwave Heating Cavities”,
Artech House Publishers, Boston and London, ISBN: 1-58053-094-X, June 2000.
[10] A C Metaxas, “Foundations of Electroheat: A Unified Approach”, Wiley, Chichester,
UK, ISBN: 0-471-95644-9, 1996.
[11] G Roussy and J A Pearce, “Foundations and Industrial Applications of Microwaves
and Radio Frequency Fields: Physical and Chemical Processes”, Wiley, Chichester,
UK, ISBN: 0 471 93849 1, 1995.
[12] A W Guy, “History of Biological Effects and Medical Applications of Microwave Energy,” IEEE Transactions on Microwave Theory and Techniques, 32 (9), Sept. 1984,
pp. 1182-1200.
[13] R I Neophytou and A C Metaxas, “Characterisation of Radio Frequency Heating Systems in Industry Using a Network Analyser”, IEE Proc. Sci. Meas. Technol., 144 (5),
Sept. 1997, pp. 215 - 222.
[14] J Haala, J v. Hagen and W Wiesbeck, “Fast Implementation of Heat Radiation in a
Self-Consistent FDTD Analysis Tool for Microwave and Hybrid Ovens”, Applied
Computational Electromagnetics Society Journal, March 2001, pp. 215 - 222.
[15] J M Osepchuk, “Microwave Policy Issues for Solar Space Power”, Space Policy, Vol.
16, Issue 2, May 2000, pp. 111-115.
[16] C A W Vale and P Meyer, “Waveguide Chokes for Microwave Heating Applications”,
MTT/EMC Section, SATCAM 2000, Lord Charles Hotel, Somerset West, Cape Town,
South Africa, Sept. 2000, 4 pages, CD-ROM ISBN: 0-620-26497-7.
[17] C A W Vale, P Meyer and K D Palmer, “A Design Procedure for Bandstop Filters in
Waveguides Supporting Multiple Propagating Modes”, IEEE Trans. Microwave Theory Tech., Boston, Vol. 48, No. 12, Dec. 2000, pp. 2496 - 2503.
[18] Roger Meredith, “Engineers’ Handbook of Industrial Microwave Heating”, IEE, London, UK, ISBN: 0-85296-916-3, 1998.
[19] I Meier and J B de Swardt, "Synthesis of Heating Patterns by Interference of Microwaves”, International Journal of Electronics, 87 (6), pp.725 - 734, 2000.