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.

Different integrated photonic sensors are investigated for the detection in the mid-infrared region of the two gases namely CO ₂ and CH ₄ . The three studied structures are ridge waveguides, based both on chalcogenide films (ChG) or porous germanium (PGe) and slot waveguides based on ChG. Waveguide dimensions are optimized to obtain the highest power factor between guided light and gas while maintaining a single mode propagation in the mid-infrared wavelength range. The achievable power factor is 1% in case of ChG ridge-waveguide, 45% for PGe-ridge, and 58% in case of ChG-slot. Extremely low limits of detection (LOD), 0.1 ppm for CO ₂ at λ = 4.3 μ m and 1.66 ppm for CH ₄ at λ = 7.7 μ m are obtained for a ChG slot waveguide, due to the large gas absorption coefficients in the mid-infrared spectral range. For PGe waveguides, low LOD values are also computed: 0.12 ppm for CO ₂ at λ = 4.3 μ m and 1.89 ppm for CH ₄ at λ = 7.7 μ m. These results show that the proposed structures could achieve competitive performance required for generic spectroscopic detection on a chip for environment and health sensing.

A new compact UWB multiple-input–multiple-output (MIMO) antenna is presented in this paper. The proposed antenna, with a compact size of 30 × 20 × 1.6 mm³, consists of a two-element microstrip line-fed pentagonal-shaped patch associated with a parasitic element and a partial ground plane. Three complementary split-ring resonator (CSRR) structures are integrated into the defected ground with the aims of reducing the mutual coupling and enhancing the bandwidth. A UWB impedance bandwidth is achieved covering the FCC band (3.1–10.6 GHz), corresponding to a reflection coefficient below −10 dB and a reduced mutual coupling below −22 dB. Additionally, acceptable limits of the diversity performance parameters are obtained. Furthermore, all the simulated outcomes of the suggested antenna are convenient for UWB-MIMO wireless applications. Measures carried out on the fabricated prototype of the antenna demonstrate good agreement between both the simulation and measurement results of the optimized two-port MIMO antenna.

Porous germanium is a promising material for sensing applications in the mid-infrared wavelength range due to its biocompatibility, large internal surface area, open pores network and widely tunable refractive index, as well as its large spectral transparency window ranging from 2 to 15 μm. Multilayers, such as Bragg reflectors and microcavities, based on porous germanium material, are designed and their optical spectra are simulated to enable SF₆ gas-sensing applications at a wavelength of 10.55 µm, which corresponds to its major absorption line. The impact of both the number of successive layers and their respective porosity on the multilayer structures reflectance spectrum is investigated while favoring low layer thicknesses and thus the ease of multilayers manufacturing. The suitability of these microcavities for mid-infrared SF₆ gas sensing is then numerically assessed. Using an asymmetrical microcavity porous structure, a sensitivity of 0.01%/ppm and a limit of detection (LOD) around 1 ppb for the SF₆ gas detection are calculated. Thanks to both the porous nature allowing gases to easily infiltrate the overall structure and Ge mid-infrared optical properties, a theoretical detection limit nearly 1000 times lower than the current state of the art is simulated.

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.