Coaxial Re∞ection Probe for Measurements of Temperature and Frequency Dependent Dielectric-properties of Low-loss Liquids

An existing measurement coaxial re∞ection probe suitable for measurements of frequency dependent dielectric properties of low-loss liquids was adapted here. A number of modiflcations made here led to an improved measurement performance in terms of signiflcantly easier evaluation of LUT dielectric properties as well as easier probe handling. Furthermore, the probe was equipped here with a heat exchanger. Therefore, it is possible to measure dielectric properties of LUT at difierent temperatures. Measurements of difierent liquids with known dielectric properties, so called standard liquids were performed as well. A comparison of the here evaluated values of dielectric properties of the standard liquids with data published in professional literature verifled here presented probe geometry and measurement procedure. Results of laboratory and fleld tests have shown that the high-power MW-fleld-induced separation of Oil and Water (O-W) emulsions has a potential to become a chemical-free alternative to con- ventional separation processes (1). The separation mechanism of this process has not been fully understood yet and there is a need for further research. In the separation mechanism tempera- ture and frequency dependent dielectric properties of the two main emulsion components, of water and oil, play an important role. While the temperature and frequency dependent model of dielec- tric properties of water already exists (2), a lack of in professional literature published dielectric properties of oils was found out. An existing measurement coaxial re∞ection probe (3) suitable for measurements of frequency dependent dielectric properties of low-loss liquids was adapted here. It consists mainly of a coaxial transmission-line section fllled with the measured liquid and short circuited at one end. Instead of the evaluation of dielectric properties of the Liquid Under Test (LUT) for every frequency point, the general model of dielectric properties of liquids, the Cole-Cole model (4) consisting of four real parameters, was used and these parameters were extracted directly. A number of modiflcations made here led to an improved measurement performance in terms of signiflcantly easier evaluation of LUT dielectric properties as well as easier probe handling. Furthermore, the probe was equipped here with a heat exchanger and therefore, it is possible to measure dielectric properties of LUT at difierent temperatures. Subsequently, it is possible to create temperature and frequency dependent models of the LUT's dielectric properties. 2. MEASUREMENT PROBE AND PROCEDURE Compared with (3), the main difierences in geometry, equivalent circuit and the measurement method used in this project are: 1. The cross-section dimensions of the probe used here are given by the 7/16 coaxial standard instead of SMA. Here, the inner and the outer radii of the measurement coaxial probe are 3.5 and 8mm, respectively. This simplifles fllling and emptying of the probe with high viscosity liquids and it also makes removal of possible air bubbles in the liquid before measurement easier.