Computer Simulation on the Relations between the Porosity and the Microwave Properties in Dielectric Ceramics
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Computer Simulation on the Relations between the Porosity and the Microwave Properties in Dielectric Ceramics Jae-Hwan Park, Jae-Gwan Park and Yoonho Kim Division of Materials, Korea Institute of Science and Technology 39-1, Hawolkok-dong, Seongbuk-ku Seoul, 136-791, South Korea ABSTRACT Effects of porosity on the microwave properties in dielectric ceramics were studied by the electromagnetic simulation. Scattering matrix S21 obtained from the network analyzer was compared to the S21 obtained from the simulation. From electric field distribution, the dominant resonant TE01δ mode could be easily determined. The effects of the porosity inside the dielectrics on the microwave properties were investigated. Quality factor decreased with the porosity and the pore size. INTRODUCTION Ceramic dielectrics have been widely studied and applied for the microwave applications such as resonators and filters [1-4]. Recently, the miniaturization of microwave circuit have strongly required high-permittivity low-loss dielectrics with good temperature stability. The tight requirements in communication bandwidth require high quality factor in microwave ceramics. As the measurements of microwave properties become more important, many studies have been reported regarding on the measurement area such cavity and field excitation method. However, the correlations between the microstructure of the dielectrics and the quality factor have been rarely considered. Generally, the microwave ceramic dielectrics are fabricated by solid state sintering process with oxide powders. Eventually, imperfections such as pore, grainboundary, and inclusions appear in the microstructure after sintering process. Although there seems to be close relations between the microwave properties and the imperfections in the microstructure, it is difficult to know the quantitative relations between microstructure and their properties. For example, it is expected that the microwave quality factor decrease with increasing porosity. However, it is difficult to correlate the decrease of quality factor with porosity quantitatively because porous ceramic bodies are likely to have not only physical pores but also imperfect second phases which have different permittivity and dielectric loss. In this study, we are to study the correlations between the microstructure and the microwave properties in dielectric ceramics by computer simulation. From this study, it might be possible to predict the influence of porosity and pore size on the microwave quality factor in more quantitative manner. EXPERIMENTS There are several methods of determining the dielectric permittivity and the quality factor of microwave dielectrics [3, 5]. Among them, cavity resonator method is very useful for the measurement of quality factor of the dielectrics. Figure 1 shows the schematic diagram of cavity R3.15.1
resonator method. By measuring RF power from port 1 and port 2, scattering matrix S21 can be determined. From the plot of S21 in frequency domain, the microwave quality factor can be determined by ca
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