A critical study of the open-ended coaxial line sensor technique for RF and microwave complex permittivity measurements

Abstract

An HP 8510 automatic network analyser and a six-port reflectometer have been used with a purpose-built calculable open-ended coaxial line sensor to measure the reflection coefficients of various materials, including dielectric reference liquids, in the frequency range 50 MHz-2.0 GHz. Factors crucial for calculable measurements have been identified including associated measurement uncertainties. The reference material measurements have been used in critical studies of (i) a commonly employed lumped equivalent circuit model of the fringing fields of the sensor, and (ii) a numerical point-matching theory of the propagating and evanescent modes at the termination of the sensor. The equivalent circuit model is shown, both theoretically and experimentally, to be generally inadequate for the full range of complex permittivities and frequencies which the sensor could otherwise cover. The point-matching theory has been used to predict the reference material reflection coefficients and the agreement with the expected behaviour measured for deionised water is to within 0.007 and 0.7" for the magnitude and phase of the reflection coefficient, respectively. An inverse solution based on the point-matching theory has been developed to derive complex permittivity from reflection coefficients and it has been used to measure various polar liquids. We conclude that the inverse point-matching theory should enable a more widespread and accurate exploitation of the sensor technique for various applications including those in biomedicine and industrial quality control.

Measurement techniques and application of electrical properties for nondestructive quality evaluation of foods—a review

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Electrical Conductivity and Dielectric Dispersion Phenomena of Concentrated TiO2 Suspensions

“…The order of magnitude of the relaxation frequency, approximated from Eq. [8], is about 10-100 MHz. Therefore, we used the impedance analyzer HP 4291A, in the 1 MHz-1.8 GHz frequency range.…”

Analysis of broadband microwave conductivity and permittivity measurements of semiconducting materials

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