Abstract
In this paper, an analytical method to estimate the complex dielectric constant of liquids is presented. The method is based on the measurement of the transmission coefficient in an embedded microstrip line loaded with a complementary split ring resonator (CSRR), which is etched in the ground plane. From this response, the dielectric constant and loss tangent of the liquid under test (LUT) can be extracted, provided that the CSRR is surrounded by such LUT, and the liquid level extends beyond the region where the electromagnetic fields generated by the CSRR are present. For that purpose, a liquid container acting as a pool is added to the structure. The main advantage of this method, which is validated from the measurement of the complex dielectric constant of olive and castor oil, is that reference samples for calibration are not required.
Highlights
This paper deals with microwave sensors based on transmission lines loaded with resonant elements
Three main sensing strategies in split ring resonators (SRRs) or complementary split ring resonator (CSRR)-loaded lines have been considered: (i) variation in the notch frequency and depth caused by resonator loading [3,4,5,6,7,8,9,10,11,12,13,14,15]; (ii) frequency splitting in transmission lines loaded with pairs of resonant elements, which is caused by asymmetric dielectric loading [16,17,18,19,20,21,22,23]; and (iii) coupling modulation sensors, where the notch depth is controlled by symmetry disruption [24,25,26,27,28,29,30,31,32,33,34]
Since the proposed method is based on the variation of the notch frequency and depth, sensor sensitivities are intimately related to the dielectric constant, εr, and the loss tangent, tanδ, of the substrate
Summary
This paper deals with microwave sensors based on transmission lines loaded with resonant elements. (ii) frequency splitting in transmission lines loaded with pairs of resonant elements, which is caused by asymmetric dielectric loading [16,17,18,19,20,21,22,23]; and (iii) coupling modulation sensors, where the notch depth is controlled by symmetry disruption [24,25,26,27,28,29,30,31,32,33,34]. The line and resonant element must be selected such that in the unperturbed state (perfect symmetry), line-to-resonator coupling is prevented
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