The Determination of Complex Dielectric Constants of Absorptive Liquids by Microwave Interferometry

Abstract

This paper describes both a traveling-wave method and a standing-wave method for determining complex dielectric constants of liquids from measurements made at 10-cm wavelength with a traveling probe immersed in a dielectric-filled slotted line. An interferometric null technique was developed for improving the accuracy of the measurements, especially in highly absorptive media. In the traveling-wave method, absolute measurements of both wavelength and absorption index can be made simultaneously; from these two quantities the complex dielectric constant is readily computed. In the standing-wave method, the absorption index is determined graphically from the power-standing-wave ratio while the wavelength is obtained by a modified null technique. For low loss media, a simplified standing-wave method is practical whereby the absorption index is obtained from measurements of the breadths of successive minima of the standing wave. Corrections for the finite resistance of the short circuit used in the standing-wave method and for conductor losses along the slotted line are fully treated.