Abstract
A microstrip highly sensitive differential sensor for complex permittivity characterization of urine samples was designed, fabricated and tested. The sensing area contains two pairs of open-stub resonators, and the working frequency of the unloaded sensor is 1.25 GHz. The sensor is easily implemented on an affordable substrate FR-4 Epoxy with a thickness of 1.6 mm. A Teflon beaker is mounted on the sensor without affecting the measurements. Numerically, liquid mixtures of water and urine at different percentages were introduced to the proposed sensor to evaluate the frequency variation. The percentage of water content in the mixture varied from 0% (100% urine) to 100% (0% urine) with a step of 3.226%, thus giving 32 data groups of the simulated results. Experimentally, the mixtures of: 0% urine (100% water), 20% urine (80% water), 33% urine (66% water), 50% urine (50% water), 66% urine (33% water), and 100% urine (0% water) were considered for validation. The complex permittivity of the considered samples was evaluated using a nonlinear least square curve fitting in MATLAB in order to realize a sensing sensitivity of about 3%.
Highlights
Resonating sensors are widely used in different applications such as: solid dielectric characterization [1,2,3], biomedical application [4,5], permittivity measurements for liquid mixtures [6,7,8], or even characterization of soil water content [9,10]
The results were used to determine the complex permittivity of the liquid mixtures, including pure water and pure urine
Due to starting with different mixture sample that are supplied in the simulation, the data range of water content that was used in the simulation was recalibrated to match the same data range of the measured samples
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. When loading the sensor with samples on one side, the symmetry is interrupted, and two resonant frequencies appear [19]. One limitation of these frequency-splitting sensors may be caused by the possible coupling between resonant elements, which is unavoidable when these elements are too close [22]. To avoid this phenomenon and to obtain the advantages of differential sensors, in this paper a sensor consisting of two identical parts is considered. The beaker is used to pour liquids in it and to make precise measurements
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