Determination of Electromagnetic Parameters of Liquid Substances in the Microwave Range
Authors:   Omsk State Technical University (OmSTU), Bogachkov I.V. 
Published: December 2024

The experimental researches of the electrodynamic properties of liquids in the microwave range is described in this work. The calculation formulas within the framework of a single-wave model and the results of trial experiments are presented. Currently, the study of the use of electromagnetic waves in the microwave range (from 0.3 GHz to 30 GHz – UHF (ultra-high frequencies) and SHF (super-high frequencies)) for heating various substances with suitable electrodynamic properties is continuing. Liquid substances are of particular interest in this field. Microwave radiation treatment can be used to solve the problems of disinfection of water, milk, and so on. Microwave heating can be used in the oil industry. An experimental measuring device was assembled to determine the electrodynamic properties of liquid substances. To measure the electrodynamic parameters of substances, a hollow segment of a coaxial line was constructed, which has a disassembly structure and can be completely filled with the test substance before measurements. The dimensions of the coaxial segment are chosen so that, in the absence of filling, its characteristic resistance (impedance) would be 50 ohms, which corresponds to the characteristic resistance (impedance) of the connecting segments of the coaxial lines, and at the same time higher types of waves would be absent in the transmission line. After calibration the measuring object was connected to the system. The frequency characteristics of the VSWR (voltage standing wave ratio) and attenuation were measured using a measuring system. In the absence of filling, the segment is coordinated with the cables of the measuring system, therefore, the reflected wave will be practical ly absent, and the signal attenuation will be determined by losses in the conductors and contact connections of the segment. When filling the line segment with the liquid substance under testing, both the VSWR and the attenuation will change. From this information, it is possible to determine the electrodynamic characteristics of the filling: the tangent of the dielectric loss angle and the complex relative permittivity. To obtain quantitative characteristics, it is convenient to use the D-matrix Keywords: microwave heating, liquid dielectric media, reflection factor, loss coefficient, microwave range, method of D-matrixes method. A scheme of the measuring installation, devices and their connections for experimental research is presented. In the range from 2 GHz to 18 GHz, experimental studies of two segments in waveguide and coaxial designs without filling with dielectrics, as well as with water filling, were carried out. The paper presents the frequency dependences of VSWR, reflection coefficient, attenuation averaged for two-line segments without filling. These data allow us to identify the systematic error of the experiment, which will allow us to correct the result for the filled segment. The analysis shows that in the unfilled segment, losses in contact connections prevail over losses in conductors. The frequency dependences of the reflection coefficient, the relative absorption power in the dielectric and the tangent of the dielectric loss angle for the experiment with water are presented. The results obtained are consistent with those published. Thus, using the considered technique, it is possible to determine the electromagnetic parameters of various liquid substances in the microwave range. Currently, the study of the use of electromagnetic waves in the microwave range (UHF (ultra-high frequencies) – 0.3-3 GHz, SHF (super-high frequencies) – 3-30 GHz) for heating various substances with suitable electro dynamic properties is continuing. Liquid substances are of particular interest in this field. Microwave radiation treatment can be used to solve the problems of disinfection of water, milk, and so on. Microwave heating can be used in the oil industry (reducing the viscosity of oily materials when pumping through pipes, melting asphalt paraffin plugs and polluting deposits in the pipes of oil wells, and so on). Most often, to determine the electrodynamic parameters of sub stances, a method of measuring characteristics is used when the sub stances under study are located inside a volumetric resonator. Despite the good accuracy, the disadvantage of this approach is obvious - it is impossible to adjust the measurement frequency parameters in a sufficiently wide operating range during experimental studies.