3D printed coaxial microwave resonator sensor for dielectric measurements of liquid

• Published in: Microwave and optical technology letters 2021-03, Vol.63 (3), p.805-810
• Main Authors: Mohammed, Ali Musa, Wang, Yi, Lancaster, Michael J.
• Format: Article
• Language: English
• Subjects: 3D printing; Acetone; Algorithms; Approximation; Broadband; Cavity resonators; coaxial resonators; Crude oil; Dielectric properties; liquids; Mathematical analysis; permittivity; Perturbation; Q factors; quality factor; Resonance; Systematic errors; Tangents; Three dimensional printing
• ISSN: 0895-2477; 1098-2760
• DOI: 10.1002/mop.32679

This paper presents a coaxial resonator for dielectric measurements of low and medium loss liquids at multiple resonance frequencies up to 8 GHz with the fundamental transverse electromagnetic (TEM) resonant mode at 2 GHz. The measurement is by filling the entire resonator cavity with the material under test and the permittivity of the material is readily extracted using simple equations. This technique provides an easy and accurate extraction method of dielectric properties without any analytical approximation and dedicated software algorithm as used in broadband open coaxial probes or the complex perturbation formula in resonator‐based methods. This significantly reduces the risk of systematic errors from the model approximation. The measured quality factor of the resonator is 2650 to 3500 depending on the resonant mode. This allows for the measurement of samples with loss tangents up to 0.05 (Acetone taken as a reference). The device was made by 3D printing and verified by measurements of several common solvents at all four resonance frequencies. The results obtained agree well with values reported in literature. Further measurements of crude oil samples were carried out and results confirmed with values obtained using other techniques.