Design and FDTD analysis of open-ended coaxial probes for broadband high-temperature dielectric properties measurements

In conjunction with ongoing research in the area of microwave processing of materials and, in particular, in the microwave sintering of ceramics, the authors found it necessary to make dielectric properties measurements at temperatures as high as 1000/spl deg/C. The authors have developed a new metallized ceramic coaxial probe for broadband, high-temperature dielectric properties measurements. Initial experience with the probe showed good experimental results in the frequency range from 500 MHz to 3 GHz, and for temperatures up to 1000/spl deg/C. To help further optimize the design of the probe, its performance was numerically simulated using FDTD. A TEM mode is excited in the coaxial feed, and the propagation, fields penetration in the sample, and the reflection coefficients were calculated using FDTD. Several probe designs were examined and the ability to make accurate and broadband measurements were examined, based on the obtained numerical results. Numerical and and graphical results illustrating some the basic guidelines of probe design, and its effective and accurate use in making dielectric measurements are presented. Parameters such as bandwidth, sample thickness, probe length, probe sensitivity to various properties of materials, and methods to increase the penetration of fields into the sample under test are discussed.<
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