Computer Modeling and Numerical Techniques for Quantifying Microwave Interactions with Materials

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COMPUTER MODELING AND NUMERICAL TECHNIQUES FOR QUANTIFYING MICROWAVE INTERACTIONS WITH MATERIALS MAGDY F. ISKANDER* "* University of Utah, Department of Electrical Engineering, Salt Lake City, Utah, 84112

ABSTRACT Computer modeling and numerical techniques provide an attractive, accurate, fast, and cost-effective means for calculating power deposition patterns and temperature distributions in materials during and after their processing using microwaves. Besides giving information on heating rates and patterns, numerical modeling and computational techniques may provide valuable information that may result in better control and optimization of the heating process. The optimum material/insulation combination for improved uniformity and efficiency of microwave sintering of ceramics and the development of procedures that may prevent problems such as temperature runaways are typical examples of attainable benefits from numerical modeling and computational techniques. In this paper, several available numerical techniques suitable for modeling 3D objects of complex geometries are described. Procedures for accurately modeling dielectric interfaces are described. Taking into account complex-incident field configurations will also be discussed. Examples illustrating the advantages, limitations, and the complementary nature of three numerical techniques based on the method of moments, finite-difference time-domain, and the spherical-wave expansion techniques are presented. It is hoped that the developed procedures and solution techniques will be beneficial to those of us involved in the complex process of microwave heating of materials and sintering of ceramics.

1. INTRODUCTION Microwave processing of materials provides several advantages that in many cases help improve the products quality, uniformity of grain structure, and yield. The ability of the microwave energy to penetrate and, hence, heat from within the product, helps reduce processing time, costs, and in some cases of ceramic processing, reduce the sintering temperature. There is also some evidence that microwave processing of materials actually provides improved microstructure and other properties of interest to the development and processing of new materials. Other reported advantages of microwave processing of ceramics include removal of water, binders, and gases without rupture or cracking, reduction of internal stress, lowering of thermal gradients, and the possibility of controlling the state of oxidation [1].

Mat. Res. Soc. Symp. Proc. Vol. 189. 01991 Materials Research Society

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There are several ongoing R & D activities in the area of microwave processing of materials. These activities clearly show that much progress has been made. Some experiments and studies that support some of the anticipated advantages of microwave processing have been successfully completed [1,2]. However, these same studies indicated that the microwave heating of materials and sintering of ceramics is a complex process and that there are many remaining problems that still ne