For an abrupt transition from a coaxial to circular waveguide with a dielectric interface in the plane of discontinuity, the input admittance has been calculated as a function of frequency and of relevant geometrical and electrical quantities. The calculations have been performed applying a mode matching technique. A simple lumped-element representation has been derived from the theoretical considerations which was found to provide an excellent description of the input admittance of the discontinuity over a wide range of values of the parameters of interest. Network parameters are discussed for transitions that are most suited as sample cells for dielectric measurements in both the time domain and the frequency domain. Results from test measurements are reported to show the agreement of our numerical predictions with precise capacitance values of other authors and also to demonstrate the sensitivity and accuracy attainable with such cells.

Complex dielectric constants of aqueous solutions of nonionic linear polymers have been measured at 10-18 frequencies in the range 0.4-40 GHz at 25 °C by an interferometric transmission method. The solutes were polyethylene oxide) and poly(vinyl alcohol) polymers of different molecular weight ( = 3400-600 000) and one sample of poly (vinyl methyl ether). To the observed data were fitted a sum of Debye relaxation functions to yield the hydration number and reorientation time of the hydration water on one hand and the relaxation strength and relaxation time of the solute on the other hand. The values of the former parameters are compared with those for poly(vinylpyrrolidone) samples and for dioxane and other monomers in order to obtain insight into the effect of macromolecular size, shape, and flexibility upon the dynamics of the surrounding water.

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