Numerical Modelling of Fringing Fields and Their Use for Complex Permittivity Measurements at High Frequencies.

摘要

A technique was developed to measure the complex permittivity of materials using an open-ended coaxial probe in contact with a semi-infinite sample. It is based on a rigorous theoretical formulation of the admittance of the probe and was tested by measurements on standard solutions at frequencies of up to 20 GHz. The technique was further used to perform measurements on aqueous ionic solutions. The data were analysed and used to the develop models to predict the dielectric parameters of NaCl and KCl solutions at a given temperature as a function of concentration with the concentration range extending from pure water to saturated salt solutions. The theoretical study and techniques were adapted to the measurement of thin samples in contact with the probe provided they are backed by a metallic plane. The success and range of applicability of the thin sample technique was tested with measurements on standard solutions. Expressions were derived for the electric field in the medium terminating the probe. These expressions were used to determine the pattern of power deposition in the medium terminating the probe. Examples are given to illustrate this statement. Complex permittivity, Ionic solutions, Thin sample, Power dissipation.