Microwave measurements of dielectric properties using a gap-coupled multi-mode coaxial resonator

• Published in: Measurement : journal of the International Measurement Confederation 2014-02, Vol.48, p.21-28
• Main Authors: Kapilevich, B., Litvak, B.
• Format: Article
• Language: English
• Subjects: Adjustable; Complex permittivity measurements; Coupling coefficient; Crude oil microwave characterization; Dielectric properties; Frequency ranges; Gap-coupled resonator; Mathematical models; Microwaves; Moisture content; Reflectance; Resonators
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2013.10.030

[Display omitted] •Gap-coupled multi-frequencies coaxial resonator.•Simple and accurate circuit model.•Simple and easy calibrating.•Curve-fitting approximation using non-linear optimization.•Wide band measurements of complex permittivity of liquids. The paper describes the measuring cell based on a gap-coupled multi-modes coaxial resonator. The role of coupling effect in forming the spectra of longitudinal odd modes has been analyzed using the circuit model of the gap-coupled resonator. The relative dielectric constant εr′ and the loss tangent tanδ of a material under test are derived from the measured input reflectance employing the least-square formulation and non-linear optimization. Experimental results are presented for the samples of crude oil with varying water content in the range 0–25%. The use of the gap-coupled configuration offers a possibility of easily adjustable coupling coefficient resulting in an application of the same measuring cells for microwave characterizations both low loss and lossy liquids and solids in a wide frequency range.