A system which enables fast and reliable measurements of the dielectric constant over continuous microwave frequency ranges for both solid and liquid low-loss materials is described. The main thrust of this work is the application of the open-ended coaxial-line probe technique, which has been used previously for soft biological materials, to low-loss solid samples. Using the instrumentation and procedure presented here, the dielectric constant for low-loss solids can be measured absolutely to ±2%–3% with routine care. The uncertainty can be reduced by about a factor of 2 by averaging several measurements. It is also smaller for liquid samples. This application features the use of relatively simple and readily available microwave components. Also, it is shown that a simple empirical relationship can be used to obtain the bulk dielectric constant from samples of a material in the form of thin slabs. The experimental results which are presented here for kapton, Teflon, Corning glass No. 0211, soda lime glass, magnesium oxide, sapphire, silicon, alumina, and lanthanum aluminate, as well as carbon tetrachloride, compare favorably with existing literature values.
Wong, W. H.; Raskovich, E. Y.; Clark, W. G.; Hines, W. A.; and Sanny, Jeff, "Measurement of the microwave dielectric constant for low-loss samples with finite thickness using open-ended coaxial-line probes" (1993). Physics Faculty Works. 56.This work addresses the effect of finite sample thickness on microwave dielectric constant measurements for thin, planar, low-loss samples using the open-ended coaxial-line probe method. Detailed measurements of the dielectric constant were carried out on a wide range of thicknesses of air samples which were backed by infinitely thick teflon and alumina dielectric media. The measurements were made at room temperature for various (50 fz) coaxial-fine dimensions, microwave frequencies 4-8 GHz, and power levels near a fraction of a mW. The results provide strong support for previously published theoretical calculations based on a boundary value problem which uses a spectral domain formulation for the aperture fields. From thin, planar samples, values of 10.4kO.5 and 25.9* 1.3 were obtained at 5 GHz and 300 K for the bulk dielectric constant of MgO and La.A1,03, respectively. The applicability of a simple empirical model based on an exponential fit is discussed.
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