In this paper, we present the design of a compact and highly sensitive microwave sensor based on a metamaterial complementary split-ring resonator (CSRR), for liquid characterization at microwave frequencies. The design consists of a two-port microstrip-fed rectangular patch resonating structure printed on a 20 × 28 mm² Roger RO3035 substrate with a thickness of 0.75 mm, a relative permittivity of 3.5, and a loss tangent of 0.0015. A CSRR is etched on the ground plane for the purpose of sensor miniaturization. The investigated liquid sample is put in a capillary glass tube lying parallel to the surface of the sensor. The parallel placement of the liquid test tube makes the design twice as efficient as a normal one in terms of sensitivity and Q factor. By bending the proposed structure, further enhancements of the sensor design can be obtained. These changes result in a shift in the resonant frequency and Q factor of the sensor. Hence, we could improve the sensitivity 10-fold compared to the flat structure. Subsequently, two configurations of sensors were designed and tested using CST simulation software, validated using HFSS simulation software, and compared to structures available in the literature, obtaining good agreement. A prototype of the flat configuration was fabricated and experimentally tested. Simulation results were found to be in good agreement with the experiments. The proposed devices exhibit the advantage of exploring multiple rapid and easy measurements using different test tubes, making the measurement faster, easier, and more cost-effective; therefore, the proposed high-sensitivity sensors are ideal candidates for various sensing applications.

In the present work, a study of a metamaterial complementary split ring resonator (CSRR) microwave planar sensor for dielectric liquid characterization is carried out using HFSS software. The design consists in a CSRR-loaded two ports rectangular patch microstrip-fed grounded planar structure. The investigated liquid sample is put in a capillary glass tube lying parallel to the surface of the sensor. The liquid test tube is deposited horizontally parallel to the surface of the planar sensor. The advantage of the design lies on the fact that it allows different orientations and multiple size possibilities of the test tube. This makes it possible to explore different resonant frequencies in the 2.1 GHz frequency band. Moreover, an optimization study is carried out to achieve a high sensitivity and a high-quality factor of the proposed sensor. To better understand the operation and to further verify the feasibility of the equivalent circuit, a parallel RLC resonant circuit is used to obtain the desired Z parameter responses Z₁₁, Z₂₂, Z₂₁. A T-shaped electrical model of the proposed sensing structure is established using Advanced Design System (ADS) software. This latter constitutes one of the principal novelties of this work, which has never been addressed so far.

This paper introduces a microwave sensor utilizing metamaterials designed for liquid characterization. It is a complementary split ring resonator (CSRR). The liquid samples are placed inside a glass tube. The interaction of electromagnetic between the resonator and the liquid to be tested modifies the resonance frequency, which changes for each complex permittivity of different samples. The proposed sensor is optimized to have consistent quality factor and a high sensitivity using the HFSS software. The measurement results are used for the validation of these results.