Measurement of the reflectivity and absorptivity of liquids, powders, and solids at millimeter wavelengths using dielectric detection by a resonator-post fixture between parallel conducting plates

摘要

The appearance of a material viewed in millimeter wavelength is a function of its reflectivity and absorptivity. These optical properties can be derived from measurement of the complex dielectric constant. Knowledge of the imaginary component is particularly important to assess the brightness of transparent or semi-transparent materials, in which the return from the back surface contributes to the overall reflection. The method presented here is well-suited to determine the dielectric constant of small samples of low-loss materials, and uses a modification of the dielectric-post resonator technique in which the sample fits into a larger, solid post fixture. The measurement frequency varies only slightly among different sample materials because the electromagnetic properties of the resonance are largely set by the supporting fixture. The method can be used to measure liquids and powders, as well as solid materials. The design and electromagnetic theory of the resonant technique are described, and the precision is discussed in context of sample measurements