System for the dielectric evaluation of powders and liquids

A free-space broadband measurement technique is proposed to determine the dielectrics properties of powders and liquids [1]. Two techniques are presented based on horizontal and vertical propagation, both of which allow for a series of measurements to be taken where the varying parameter is thickness of material under test (to overcome the challenge of the unknown electrical length). The horizontal propagation measurements would require an extra containment layer for powders and liquids, which would have consequent mechanical and also computational difficulties. The vertical propagation measurements on the other hand show more promise, both in terms of mechanical containment and also in the inversion of the measured S-parameters to arrive at the complex electric permittivity. The measurements were performed in a large hall and also in an anechoic chamber. To minimise measurement errors a free-space Thru-Reflect-Line/Match (TRL/M) calibration technique was performed. The initial results reported here are for various glass thicknesses, of unknown chemical composition, in the frequency range of 0.8-6 GHz, although the application to powders and liquids will be apparent.