Passive Reference Reflectometry for Determining Multilayer Media Levels and Parameters

This paper proposes a method of passive reference reflectometry based on the use of references with known localization and constant reflection coefficients within the transmission path. A comparison of different approaches to implementing passive references is presented. To enhance identification reliability, paired inhomogeneities are introduced as references, generating responses with opposite polarities. Model and experimental studies are carried out with the use of a 519-mm in length coaxial probe, with diameters of the screen and central conductor of 12 and 5 mm, respectively, with the inclusion of five equidistant paired references. The applicability of the passive reference reflectometry method for determining the relative permittivity along the path length is concluded. For this probe, when measuring a multilayer medium consisting of air, technical oil, and distilled water, the experimental error of the relative permittivity was less than 7.9% and that in the cases when the interface boundaries are located near the references is up to 34.7%. Thus, the application of the proposed method allows for determining or refining the relative permittivity of layers. This can be useful in the problems of level measurement to improve the accuracy of level determination and to obtain information about the qualitative characteristics of layers of multilayer media.