IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 42, NO. 5, MAY 1994 793

FDTD Simulation of Microwave Sintering of Ceramics in Multimode Cavities

Magdy F. Iskander, Fellow, IEEE, Ray L. Smith, Student Member, IEEE, A. Octavio M . Andrade, Member, IEEE, Hal Kimrey, Jr., and Lee M. Walsh

Abstract-Microwave sintering of ceramics in multimode cav- ities, particularly the use of picket-fence arrangements, has re- cently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique “microwave effect” has been observed.

At present, various aspects of the sintering process such as preparation of sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as Sic rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide an improved understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process.

In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a ceramic loading plate placed at the base of the cavity. The FDTD simulation thus provides realistic representation of a typical sintering experiment. Aspects that have been successfully simulated include the effects of various types of insulation, the role of Sic rods on the uniformity of the resulting microwave fields, and the possible shielding effects that may result from excessive use of Sic. These results as well as others showing the electromagnetic fields and power-deposition patterns in multiple ceramic samples are presented.

I. INTRODUCTION ECENTLY, there have been reports of a unique charac- R teristic known as the “microwave effect” that may result

from microwave sintering of ceramics [ I 1-[3]. Specifically, lower sintering temperatures, smaller grain size, and lower activation energies were reported. With the significant interest and continued publication of results infemng advantages of us- ing microwaves rather than conventional sintering of ceramics, there has been a significant need to better model a microwave sintering process and simulate realistic sintering experiments. There is no doubt that before the full commercial utilization of this technology, a detailed understanding of the basic nature of the microwave interactions as a function of frequency, geometry, and temperature must be developed, and tradeoffs between the use of single- and multimode cavities should be understood. Furthermore, the effect of the sample sizes and

Manuscript received April 10, 1992; revised July 19, 1993. The first three and the last authors are with the Department of Electrical

Engineering, University of Utah, Salt Lake City, UT 84112. Mr. Hal Kimrey is with Oak Ridge National Laboratory, Oak Ridge, TN 37831.

IEEE Log Number 9216815.

shapes of the effectiveness of the microwave sintering must be analyzed and the use of stimulus such as S ic rods in a picket-fence arrangement must be understood and optimized.

In this paper, we used the finite-difference time-domain (FDTD) technique to model and simulate realistic microwave sintering experiments using multimode cavities. Although the FDTD method has been previously used to analyze eigenvalue and dielectric resonator problems [4]-[6], the contribution discussed in this paper is different than those reported ear- lier. Differences include: l ) this paper deals with sintering experiments in multimode cavities rather than in single-mode resonant structures; 2) a realist multimode structure that in- cludes the feed waveguide and a ceramic base plate used for sample placement were used in the FDTD model; and 3) the field distribution in an empty cavity was initially adjusted so as to provide reasonably accurate representation of experimentally measured data using liquid crystal sheets. These, as well as the fact that the prime interest of this paper is to model EM absorption patterns in realistic sintering experiments, make the contribution of this paper different from previously reported ones.

11. NUMERICAL BACKGROUND Throughout this paper, results will be presented that were

produced using an FDTD code available at the University of Utah [7], [8]. Although this code was developed to model both interstitial antennas and noninvasive applicators for hy- perthermia applications, it required simple modifications to successfully model realistic microwave sintering experiments [7]. The FDTD code was chosen for its ease of operation and the ease at which it can be adapted to different geometries. Furthermore, the assumed highly conducting cavity walls naturally limit the computation domain and hence minimize computational problems associated with absorbing boundaries. For high Q cavities, however, the convergence of the FDTD code is rather slow and the solution may take a long time to reach steady state.

The code uses Yee’s cells [8], [9] to discretize the compu- tational domain and is, in fact, similar to the code developed originally in [lo]. Since the code was developed for use in unbounded space, it included the usual radiation boundary conditions as described in [ 1 11. The extent of the modifications made to the available code are centered around the removal of the majority of the radiation boundary conditions (RBC’s) (except at one end of the waveguide feed region where first- order Mur boundary conditions are used) and replacing them

0018-9480/94$04.00 0 1994 IEEE

194 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 42, NO. 5 , MAY 1994

Microwave Oven /

rofoam Supports

Front View \ Liquid Crystal S h e e t

Fig. 1. Experimental arrangement used to map power distribution pattern in a sintering microwave oven. Color temperature pattem in liquid crystal sheets is proportional to EM power distribution pattem when short (typically 10 s at 700 W) heating time is used. The dimensions of the microwave sintering oven are 40 x 30 x 40 c d .

with metal boundaries of varying conductivities. The program was also modified to allow for the use of a waveguide source to feed the multimode sintering cavity. By removing the RBC’s and replacing them with conducting walls, the overall FDTD code was greatly simplified, thus allowing for savings in both computational time and storage requirements. These savings were helpful in that some of the cavities have a large Q when left unloaded, which increases the time required to reach a steady-state condition. Besides these aforementioned modifications, the used FDTD code was basically similar to the one reported in earlier publications [7], [ 8 ] .

The majority of simulation cases were run at 2.450 GHz with a cell size, A, of 1 cm or about 1/12th of the free-space wavelength. Although this limited the resolution of the model, it was helpful in identifying trends before large computational resources were brought to bear on the model. The accuracy of this assumption will be discussed in Section IV. The time steps were taken to be A/2c where c is the speed of light in free space. This led to a time step in regular computer runs of approximately 6.67 ps. As trends became apparent, the cell size could then be reduced to allow further investigation of the individual phenomena. The code was run on an IBM 3090 computer and a typical cpu time averaged 1800 s.

111. OVERVIEW OF THE SOLUTION PROCEDURE

An important consideration in the modeling process de- veloped in this paper is to provide useful information on the relationship between different parameters that critically influence the microwave sintering process. Many experimental measurements were made at Oak Ridge National Laboratory [l], [3], and the developed numerical model is expected to confirm these observations and hopefully lead to optimized designs in future sintering experiments.

The first step in the simulation process was to determine the EM power distribution pattern in a microwave cavity typically used for sintering in our laboratory. To this end, liquid crystal sheets were placed horizontally using Styrofoam supports to map the power distribution pattern at successive planes throughout the cavity. Fig. 1 shows the experimental arrangement used in making the temperature distribution pat- terns while Fig. 2 shows a typical result of the sintering oven available in our laboratory. For short heating times (less than 10 s), the temperature distribution is linearly proportional to the EM power pattern desired in our simulation. It should also

Fig. 2. Typical temperature distribution pattern obtained from color patterns measured using liquid crystal sheets. The relationship between the measured color pattern and the shown temperature distribution was calibrated separately using temperature-controlled water path.

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Fig. 3. Typical steady-state electric-field distribution pattem in an empty cavity obtained by assuming several possible modes on the excitation planes placed within the cavity. The relative amplitudes of the various modes are varied so as to obtain a field distribution pattern that resembles measured values. Reported results were obtained when six modes of equal amplitude were used on the excitation planes.

be noted that this arrangement was not intended to produce actual field values, but only qualitative results to help in developing a simulation with initial field-distribution values in an empty cavity that reasonably resemble measured data.

A model of the cavity is then developed using FDTD to produce an EM field pattern similar to the measured data. Two FDTD modeling procedures were adopted for this purpose. The first model simply consisted of choosing a set of modes that could exist independently and simultaneously within a small band of frequencies centered around the cavity operating frequency of 2.45 GHz. The cavity is then forced to converge to this set of modes at the excitation planes and the solution is allowed to reach a steady-state condition elsewhere in the cavity. The resulting field pattern was observed and the amplitudes of the modes are adjusted to help match the measured field patterns. Typical results using this method are shown in Fig. 3, which was produced using six different modes of equal amplitude. The second procedure involves the modeling of the feed waveguide in the cavity. The waveguide

ISKANDER et al.: FDTD SIMULATION OF MICROWAVE SINTERING OF CERAMICS IN MULTIMODE CAVITIES 195

I I I -----.. A Insulation I

- 40cm h’( Half Hei ht WR 340 Waveguide

Fig. 4. Model used in the FDTD simulation of the sintering experiments. Although a typical mode stirrer was not included in the simulation, the geometry, dimensions, and location of the feed waveguide were changed to adjust the field patterns in the empty cavity so as to correlate with measured results.

feed is placed horizontally along the bottom of the cavity in an arrangement that is similar to the feed arrangement used in the construction of the microwave oven used for sintering. A ceramic base plate was included above the feed waveguide first to simulate the experimental arrangement where the ceramic plate provides a place where the sample location is well defined and also to help improve the computational efficiency of the FDTD code, since having additional losses in the cavity helps shorten the time required to converge to steady state. The feed waveguide dimensions were varied and discontinuities (flares and posts) were introduced to provide some degree of mode-stirring capabilities that help reproduce the measured field-distribution pattern. Reflections at one end of the waveguide feed were minimized by introducing a first- order Mur absorbing boundary condition at roughly a half guide wavelength behind the excitation plane. Fig. 4 shows the model used in the numerical simulation, while Fig. 5(a) shows the obtained steady-state result for the EM field distribution in an empty cavity when a straight length of a waveguide is used as a feed at one end and terminated at the other. Fig. 5(b) shows the resulting steady-state EM field pattern when the feed waveguide includes a flared transition to the empty cavity. From Fig. 5 it may be seen that adjusting the feed waveguide geometry and dimensions provide variables suitable for adjusting the field patterns in the empty cavity. The results from Fig. 5(b) also reasonably resemble the measured liquid crystal temperature pattern shown in Fig. 2.

IV. RESULTS

After obtaining an EM field pattern in the empty cavity that correlates well with measured data, realistic microwave sintering experiments in a multimode cavity were simulated using the FDTD code described above. Ceramic samples and surrounding insulations are basically placed in the cavity as shown in Fig. 4, and the steady-state EM power deposition pattern is calculated in both the sample and the insulation. The parameters expected to play critical roles in microwave sintering experiments are then varied to determine their effect on the steady-state EM field distribution pattern. After an extensive number of simulation runs, observations were made

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(b)

Fig. 5. Steady-state electromagnetic field patterns inside an empty cavity (a) when a straight section of the feed waveguide was used and (b) when a flared section of the feed waveguide was used. The difference in results of (a) and (b) illustrate the ability to modify field patterns in an empty cavity so as to correlate with experimentally measured results using liquid crystal sheets. The dimensions of the sintering microwave oven are 40 x 30 X 40 cm3.

and guidelines were developed towards the optimization of the sintering process.

Before presenting numerical results, however, it is important that we show that the FDTD solution has converged and does provide adequate resolution when a 1 cm FDTD cell size is used. It is very desirable to have a variable mesh size capability in the FDTD code so that finer mesh may be used in the sample and insulation regions and larger mesh in the empty cavity space. Since our code does not have the variable mesh size capability, we decided to use a similar but smaller 20 cmx20 c m x l 5 cm cavity model (half of the linear dimensions of the model shown in Fig. 4) to check the adequacy of the resolution that may be obtained from a 1 cm FDTD cell size. Specifically, the total electric-field distribution in the cavity was calculated when a 2 cm cube sample surrounded by a 6 cm-thick insulation was heated in the smaller cavity using four S ic rods as stimuli. Three different cell sizes were used in three separate runs, and the obtained results are shown in Fig. 6. From these results, it may be seen that while the 0.33 cm cell size (approximately 0.15 X inside the Sic) provides an improved resolution of the

796 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 42, NO. 5, MAY 1994

Fig. 7. Steady-state electric-field (magnitude) pattern in an unsintered (green) ceramic sample surrounded by 3-cm-thick insulation. The dielectric constant and conductivity of the sample are F, = 4.13 and u = 6.2 x l o p 6 S/m, respectively, while those of the surrounding insulation were assumed t7. = 1.537 and o = 15.374 x l o p 6 S/m, respectively. The ceramic sample is of cylindrical shape of 2-cm radius and 6 cm long. The dimensions of the microwave oven are the same as those of Fig. 5 .

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Fig. 6. Electric-field (magnitudc) distribution in a 20 cmx20 cmx 15 cm multimode cavity loaded with a 2 cm3 sample surrounded by 8 cm-diameter insulation. Four I cmx 1 c m x 4 cm S i c rods were used in this simulation. (a) FDTD cell size is 1 cm. (b) FDTD cell size is 0.5 cm. (c) FDTD cell size is 0.33 cm, which is approximately 0.15 X in S i c at the simulation frequency of 2.450 MHz. It may be observed that the field distributions in the sample and inwlation are generally the same.

electric-field distribution, the field-distribution results obtained from the three cases are generally the same, particularly in the sample and insulation regions. In other words, the 1 cm cell-size results provide a useful general description of the desired information. Therefore, the remaining simulation of

Fig. 8. Steady-state electric-field (magnitude) distribution pattem in an un- sintered (green) ceramic sample surrounded by 3-cm-thick insulation. The dimensions and dielectric properties of the sample are the same as those of Fig. 7, while the dielectric constant of the insulation was changed from cr = 1.537 to F, = 10.

the various parameters of interest will be based on a 1 cm cell size since it provides a substantial savings on the memory requirements of our FDTD code.

First, the effect of the type of insulation material and its dimensions on the resulting EM field pattern in the sample was examined. Figs. 7 and 8 show the steady-state EM field distri- bution in a cavity in which a green (unsintered) ceramic sample was placed surrounded by an insulation of a different value of E,.. In many of these sintering experiments, the insulation plays a valuable role in containing the heat and hence enhancing the sintering process. The dimensions and complex permittivities of the sample and the insulation used in this simulation run are given in Figs. 7 and 8. In some cases, such as in Fig. 8, it may be seen that the fields were actually drawn into the sample while in others, such as Fig. 7, fields were concentrated just outside the sample. This change in the field pattern was clearly caused by the change in the value of the dielectric

ISKANDER et al.: FDTD SIMULATION OF MICROWAVE SINTERING OF CERAMICS IN MULTIMODE CAVITIES

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Fig. 9. Steady-state electric-field (magnitude) distribution pattern in the unsintered ceramic sample of Fig. 7. All dielectric parameters and dimensions are the same as those of Fig. 7 except that the conductivity of the insulation was changed from o = 1.537 x lop5 S/m to 0.09 S/m.

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1 E46 o.oO01 0.01 1 E-05 0.001 0.1

Conductivlty of insulation (S/m)

Insulation -.-----. ceramic sample - Fig. 10. Steady-state total power absorbed in sample and insulation vs. change in conductivity of the insulation. Changing the insulation conductivity to values near 0.001 S/m does not affect the total power absorbed by the sample. Further increase in the conductivity of the insulation effectively shields the sample and results in a reduction in the total power absorbed by it. The dimensions and other electrical properties of the sample and insulation are the same as those of Fig. 7.

constant of the insulation from 1.537 to 10. The different locations of the field maxima and minima in the green sample result in nonuniform heating of the sample and can result in undesirable mechanical properties or even thermal runaway problems which may result in the destruction of the sample.

The conductivity of the insulation can have a significant ef- fect on the EM field distribution pattern in a typical microwave sintering experiment. Fig. 9 shows the effect of increasing the conductivity of the insulation from 1.537 x S/m to 0.09 S/m, while leaving the other properties the same as in Fig. 7. From these results it is clear that the conductivity of the insulation plays an important role and, in particular, the increase of the conductivity results in an increase in the scattered fields from the sample and insulation arrangement. The effect of changing the conductivity of the insulation is further investigated in Fig. 10, which shows the variation

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Fig. 11 . Steady-state electric-field (magnitude) distribution pattern in a green ceramic sample surrounded by 3-cm-thick insulation when four S i c rods were placed in the insulation to stimulate the sintering process at lower temperatures. The dimensions of the sample and the insulation are the same as those of Fig. 7. The S i c rods are of 0.6 cm radius and 10 cm long. The dielectric constant and conductivity u of the S i c rods are 29.363 and 0.9 S/m, respectively.

of the total power absorbed in the ceramic sample and the insulation versus the increase in the conductivity of insulation. From Fig. 10 it may be seen that increasing the conductivity of the insulation up to values of 0.001 S/m may help draw more power from the feed waveguide while maintaining the total amount of EM power absorbed by the sample constant. If the conductivity of the insulation exceeds 0.001 S/m, on the other hand, the absorbed EM power by the sample is reduced while the power absorbed by the insulation continues to increase.

One of the more successful microwave sintering experi- ments involves the use of S ic rods in a picket-fence ar- rangement to help the heating process, particularly at lower temperatures. In some sintering experiments, the number and arrangement of these S ic rods is critical to the success of the experiment. The developed FDTD code was used to examine various aspects of the use of S ic rods to stimulate sintering of ceramic samples. Fig. 11 shows the obtained results for the EM field distribution pattern when 4 Sic rods were used as a stimulus in the same arrangement as in Fig. 7. It can be seen that the EM fields tend to concentrate around the S ic rods. However, as more Sic rods are added to the model, as in Fig. 12 where 12 rods were used, the electric-field distribution in the sample decreases as the energy is mostly absorbed in the S ic instead of the ceramic sample. Although such a trend may be difficult to see by comparing Figs. 11 and 12, careful examination of numerical values shows that the electric-field value at the center of the sample is 4.9 x V/m in Fig. 12 as compared with 11.05 x

A drawback of the use of the stimulus arrangement is, therefore, related to the fact that an excessive use of S ic rods and the fact that they have high electrical conductivity may hinder the penetration of the EM energy to the ceramic samples. If such reduction occurs, the sintering will be mainly due to conventional heating (heat transfer from Sic rods to sample), and this may in turn result in the reduction in the often-desirable “microwave effect.” Another drawback of using Sic rods is related to the lowering of the Q’s of the

V/m in Fig. 11.

798 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 42, NO. 5 , MAY 1994

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Fig. 12. Steady-state electric-field (magnitude) distribution pattern in the same sintering arrangement as that of Fig. 11 except that 12 (instead of 4) Sic rods were used as stimuli.

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Fig. 13. Steady-state electric-field (magnitude) distribution in four ceramic samples placed in the microwave sintering cavity of Fig. 7. Each sample is cylindrical in shape with a radius of 2 cm and 6 cm long. The insulation is 2 cm thick. No S i c rods were used in this simulation. The dielectric properties of the sample and insulation are the same as those in Fig. 7.

various cavity modes in the multimode microwave sintering cavity. This will clearly result in reduced electric-field intensity and to a reduction of the efficiency of the sintering process. It is, therefore, suggested that a balance should be observed and the number of S i c rods should be kept to a minimum, say 4 to 6 rods, depending on the size of the sample.

In some sintering experiments, multiple samples might be used. Fig. 13 shows the steady-state electric-field distribution when four samples were used. From Fig. 13 it may be seen that for such an arrangement, excessive electric field is localized in the insulation layer and that the inclusion of appropriately located S i c rods may result in more favorable distribution of the electric-field pattern. From Figs. 13 and 14, we conclude that S i c rods may play a role in the sintering experiment both by absorbing EM power and subsequently conventionally heating the sample until sufficiently higher conductivity of the sample is achieved at elevated temperatures, and also by modifying the field distribution in the sintering cavity so as to provide better uniformity in the field values at the locations of the ceramic samples.

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Fig. 14. Steady-state electric-field (magnitude) distribution in the four ce- ramic samples of Fig. 13. Four S i c rods were used in this case and a significant change in the field distribution pattern was observed.

V. CONCLUSIONS

An FDTD code was developed and successfully used to model some of the many factors that influence a realistic microwave sintering process in multimode cavities. The sim- ulation procedure is based on an initial field distribution in an empty cavity that is similar to an experimentally measured pattern using liquid crystal sheets. The dimensions of the waveguide feed were adjusted and discontinuities were added to provide some controls on the resulting EM field distribution pattern in the empty cavity so as to resemble the measured data. The accuracy and adequacy of the 1 cm cell size used in the calculations were also checked by making calculations for 1 cm, 0.5 cm, and 0.33 cm cell sizes.

The developed FDTD code was then used to simulate and examine several parameters of interest in a typical microwave sintering experiment. This includes the conductivity of the insulation surrounding the sample and the role of the S ic rods in modifying the EM field distribution pattern in the sample. It is shown that while an increase in the conductivity of the insulation may stimulate the sintering process by raising the temperature of the insulation and subsequently the sample, excessive increase in the conductivity on the insulation decreases the penetration of the EM fields to the sample and hence reduces the desirable “microwave effect.” It is also shown that a similar effect may result from an excessive use of S ic rods as a stimulus.

The above obtained results as well as others including the simulation of multiple samples in a microwave sintering experiment certainly helped in identifying some trends that are important in understanding and optimizing the microwave sintering process. Future plans include the continued use of the FDTD code to develop guidelines regarding the optimization of the sintering process in multimode cavities. Additional efforts to integrate the FDTD code with a heat-transfer com- puter program to calculate the temperature distribution pattern in a sintering experiment are also underway. This latter ef- fort should also help make quantitative comparison between simulated and experimental results.

ISKANDER rr a/: FDTD SIMULATION OF MICROWAVE SINTERING OF CERAMICS IN MULTIMODE CAVITIES 799

REFERENCES M. A. Janney and H. D. Kimrey, “Microwave sintering of alumina at 28 GHz,” in G. L. Messing, E. R. Fuller, and H. Hausner, Eds., Ceramic Power Science I I , Westerville, OH, American Ceramic Society, 1988, pp. 919-924. Y. L. Tian, D. L. Johnson, and M. E. Brodwin, “Ultrafine microstructure of A1203 produced by microwave sintering,” in G. L. Messing, E. R. Fuller, and H. Hausner, Eds., Ceramic Power Science 11, American Ceramic Society, Westerville, Ohio, 1988, pp. 925-932. H. D. Kimrey and M. A. Janney, “Design principles for high frequency microwave cavities,” Proc. Mater. Res. Soc., vol. 124, p. 367, 1988. D. H. Choi and W. J. R. Hoefer, “The finite difference time domain method and its application to eigenvalue problems,” IEEE Trans. Mi- crowave Theory Tech., vol. MTT-34, pp. 1464-1469, 1986. A. Navarro, M. J. Nunez, and E. Martin, “Finite difference time domain FFT method applied to axially symmetrical electromagnetic resonant devices,” IEE Proc., vol. 137, Part H, pp. 193-195, 1990. -, “Study of TEo and TI10 modes in dielectric resonators by a finite difference time domain method coupled with the discrete Fourier transform,” IEEE Trans. Microwave Theory Tech., vol. 39, pp. 1 4 1 7 , 1991. M. F. Iskander, “Computer Modeling and Numerical Techniques for Quantifying Microwave Interactions with Materials,” in W. B. Snyder, W. H. Sutton, M. F. Iskander, and D. L. Johnson, Eds., Microwave Pro- cessing of Materials II. Published by the Materials Research Society, vol. 189, 1990, pp. 149-171. P. C. Cherry and M. F. Iskander, “FDTD analysis of power deposition patterns of an array of interstitial antennas for use in microwave hyperthermia,” IEEE Trans. Microwave Theory Tech., Aug. 1992. K. S. Yee, “Numerical solution of initial boundary value problems in- volving Maxwell’s equations in isotropic media,” IEEE Trans. Antennas Propagat., vol. AP-14, p. 302, 1966. A. Taflove and K. R. Umashankar, “The finite-difference time-domain method for numerical modeling of electromagnetic wave interactions with arbitrary structures,” in M. A. Morgan, Ed., Finite Element and Finite-Difference Methods in Electromagnetic Scatter. Amsterdam: El- sevier, 1990. G. Mur, “Absorbing boundary conditions for the finite-difference ap- proximation of the time-domain electromagnetic field equations,” IEEE Trans. Electromag. Compat., vol. EC-23, p. 377, 1981.

Magdy F. Iskander is Professor of Electrical En- gineering at the University of Utah He is also the Director of the Engineering Clinic Program, which he established in 1986 He is also the Director of the NSFOEEE Center for Computer Applications in Electromagnetic Education and Director of the State Center of Excellence for Advanced Computer- Aided Science and Engineering Education He has received the Curtis W McGraw ASEE National Research Award for outstanding early achievements by a univmity faculty member, the ASEE George

Westinghouse National Award for innovation in Engineering Education, and the 1992 Richard R Stoddard Awad from the IEEE EMC Society

He edited two special issue\ of the Journal of Microwave Power, one on “Electromdgnetics and Energy Applications,” M a c h 1983, and the other on “Electromagnetic Techniques in Medical Didgnosis and Imaging,” September 1983 He also edited a special issue of the ACES Journal on computer-aided electromagnetics education He authored one book on Electrornagnetic Fields and Waves, (Prentice-Hall, 1992), edited the CAEME Software Book, Vol I , 1991, and coedited two book$ on Microwave Processing of Materials, both published by the Materials Research Society in 1991 and 1992 He ha5 published over 100 paper\ in technical journdls and made numerous presentdtions in technical conferences

Dr lskdnder is the editor of the Joumal Computer Applications in Engi- neering Education, publi5hed by Wiley He is a member of the National Resedrch Council Committee on Microwave Processing of Materials His research intere3t include the use of numerical techniques in electromagnetics

Ray L. Smith (S’92) was born in Salt Lake City, Utah. He received B.S. and M.E. degrees in electri- cal engineering from the University of Utah in 1991 and 1993, respectively.

From 1991 to 1993, Mr. Smith worked as a Re- search Assistant. His research interests are numer- ical techniques for solving engineering problems, particularly as applied to electromagnetics.

A. Octavio M. Andrade (S’70-M’72) was born in Sao Paulo, Brazil, on May 23, 1945. He received the B.Sc. degree in Electrical Engineering from Escola de Engenharia Maua, Sao Paulo, Brazil, in 1969. He received the M.Sc. in Electrical Engineering degree in 1972 and the D.Sc. degree in 1981, both from the Polytechnic School of the University of Sao Paulo, Brazil.

In 1970 he was awarded a student fellowshio from the Foundation for Research Support of the State of Sao Paulo (FAPESP) for research work on

his M.Sc. Thesis. From 1970 until 1972, his work was concentrated on the design and construction of TEM-mode stripline directional couplers, as well as teaching undergraduate courses on Transmission Lines and Microwaves. Beginning in 1973, he has directed his research interests to the area of Power Applications of Microwaves, especially in developing novel techniques for the determination of the dielectric properties of materials, which led to his D.Sc. Thesis. In 1975, he was on a short stay at the University of Manitoba, Winnipeg, Canada, where he worked on the development of cavity resonator methods for the determination of complex dielectric constant of materials, and designed a partially-filled resonator technique for such measurements as a function of temperature. His research and teaching activities at Escola de Engenharia Maua until 1989 continued to be directed towards the implementation of dielectric constant measurement techniques, along with the design and construction of numerous high-power microwave applicators and components. From 1982 to 1984, he directed part of his research interests to the area of biological effects of microwave radiation. In 1984 he received a post-doctoral fellowship from the British Council and was on a short stay at the Cambridge University Addenbroke’s Hospital School of Clinical Medicine, England, where he followed the investigations being conducted on microwave hyperthermia for cancer treatment.

His present fields of interest include the use of numerical techniques in electromagnetics and the use of microwave methods for materials character- ization and processing, and he has published and co-authored many papers and made numerous presentations on the subject in technical conferences.

In 1989 Dr. Andrade was Chairman of the Steering Committee of the 1989 SBMO International Microwave Symposium held in Sao Paulo, Brazil, and sponsored by the Brazilian Microwave Society (SBMO), of which he is a founding Member. From 1990 to 1993 he was Visiting Professor at the Department of Electrical Engineering of the University of Utah, Salt Lake City, where he was engaged in numerous teaching and research activities in the areas of Antennas and Microwaves. He was advisor of the Oak Ridge National Laboratories and Hewlett-Packard Clinics of the Engineering Clinic Program for three consecutive years. He also coauthored a chapter on the first CAEME (Computer Applications in Electromagnetics Education) Book in 1991.

Dr. Andrade is also a member of the Review Board of the Joumal on Computer Applications in Engineering Education, published by Wiley. He is presently Professor of Electrical Engineering at Escola de Engenharia Maua, Sao Paulo, Brazil.

800 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL 42, NO. 5 , MAY 1994

Harold D. Kimrey, Jr. received the B.S. and M.S. degrees in electrical engineering from North Car- olina State University in 1980 and 1982, respec- tively.

From 1981 to 1991, he was with the research staff in the Fusion Energy Division at Oak Ridge National Laboratory, where he lead the efforts for developing microwave technology for ceramic pro- cessing. He was also involved in research on mod- eling of gyrotron ceramic output windows, devel- opment of microwave systems for several fusion

research machines including the Advanced Toroidal Facility, the Radio Frequency Test Facility, and the Elmo Bumpy Torus. He was involved in the National Gyrotron Development Program as technical monitor. In 1991, he joined the Metals and Ceramics Division at Oak Ridge National Laboratory as a Development Staff member. His responsibilities are focused on program development in the microwave processing area. He is the author of over 40 publications in journals, conferences, and symposium proceedings. He is the holder of four patents with seven pending in the area of microwave devices and applications. He is the principal investigator on a microwave diamond synthesis project using high-frequency microwaves at 28 GHz. He is the program manager for the ORNL Engineering Clinic at the University of Utah, where a modeling effort has begun to better understand microwave interactions with materials. He is the principal engineer for microwave equipment development in the division including a 5000 I, 2.45 GHz and 28 GHz microwave furnace.

In 1989, Mr. Kimrcy cofounded a new company, Microwave Materials Technology, which specializes in the application of microwave energy to materials processing. Products include conventional and custom microwave equipment, consulting, toll processing of materials, and contract research.

ii I

Lee M. Walsh was bom in Madison, Wisconsin, on October 14, 1956. He received his B.S.E.E. from the University of Utah in June 1993.

In June 1993, Mr. Walsh started his career in elec- trical engineering with Motorola’s Semiconductor Products Sector in Austin, Texas. He is a Product Engineer for the Customer Specified Integrated Cir- cuits division where he helps to characterize and market a brand new micro controller, the HC08.