Contents 1 Introduction
The study of the dielectric properties of high-loss liquids and powders is of great importance in applications like radar absorbing material design, remote sensing, and powder technology. However, noncontact evaluation and characterization of liquids, especially chemically active reagents is a problem for many industries, and currently there is no method available to characterize such liquid samples [1]. In recent years, there has been increasing interest in using free- space techniques for measurement of electrical properties of materials which can be solids or liquids. Ghodgaonkar et al [2], [3] have reported that free-space methods are nondestructive and noncontact; hence, they are especially suitable for measurement of the complex permittivity under high-temperature conditions. Therefore, in this paper, we present a method for measurement of dielectric properties of lossy liquids which is modification of reflection- transmission method reported by Ghodgaonkar et at [2]. The inaccuracies in free-space microwave measurement system [2] is due to diffraction from the sample which is minimized by using spot focusing horn lens antennas. Also, errors due to multiple reflection between antennas were minimized by using free-space LRL (Line, Reflect, Line) calibration technique and time domain gating which is a feature of VNA. The liquid is contained in a Plexiglas container which has two plates of material with known dielectric properties. In this method, the free-space reflection (S11) and transmission coefficients (S21) are measured for Plexiglas container filled with liquid. Complex permittivity is evaluated by the reflection-transmission method after removing effect of Plexiglas container. Complex permittivity values are reported for lossy liquids such as ethanol, methanol, ethyl glycol and N-Propyl Alcohol.
