Microwave gas sensor based on graphene aerogel for breath analysis

Exhaled breath can be used for early detection and diagnosis of diseases, monitoring metabolic activity, and precision medicine. In this work, we design and simulate a microwave sensor in which thin graphene aerogels are integrated into rectangular microwave waveguides. Graphene aerogels are ideal sensing platforms for gases and volatile compounds as they combine extremely high surface-to-volume ratio and good electrical conductivity at RF and microwave frequencies. The latter is modified by exposure to different gases, and -when integrated into a waveguide- these changes result in significant shifts in transmission and reflection scattering parameters. We model the aerogel as a graphene grid with hexagonal openings of size 22.86×10.16×0.1 mm3, characterized by an air volume equal to about 90 % of its entire volume. This grid is used as a building block for modeling thicker samples (up to 9 mm), To simulate the variation in the dynamic conductivity of the graphene sheets as a consequence of the absorption of gaseous molecules, a sweep of the chemical potential from 0.0 e V to 0.5 e V with steps of 0.1 e V was used. The results show a significant variation of the waveguide transmission scattering parameters resulting from the gas-induced modification of the graphene conductivity, and hence the potential of the proposed sensor design for breath analysis

Microwave gas sensor based on graphene aerogels

— In this article, the experimental demonstration of a novel microwave gas sensor based on graphene aerogel is presented. This device makes use of a highly porous structure of the aerogel in combination with the modulation of graphene AC conductivity upon exposure to vacuum and ambient air. As a proof of concept, we integrate the graphene aerogel into rectangular waveguides and measure its scattering parameters by a Vector network Analyzer (VNA). The aerogel is characterized by a combination of scanning electron microscopy and four-probe DC measurements. The aerogel is integrated into WR-90 waveguides by custom-designed support and wave propagation is tested over the 8-12 GHz frequency range (Xband). By exposing the aerogel to either air or a moderate vacuum, clear shifts in the waveguide scattering parameters are observed. In particular, changes of ≈ 3 dB and ≈ 1 dB in the transmission and reflection parameters of the waveguide are obtained, respectively. Moreover, the sensor exhibits excellent reproducibility when exposed to alternating cycles of air and vacuum, proving that the shifts in microwave transmission and reflection are caused by changes in the conductivity of the graphene aerogel due to the absorption and desorption of gas molecules. These proof-of-concept results pave the way for the development of a new class of gas sensors for applications such as breath analysis

High-sensitivity narrow-band CSRR-based Microwave Sensor for Monitoring Glucose Level

In this paper, a high-sensitivity narrow-band microwave sensor based on a complementary split-ring resonator (CSRR) to detect glucose concentrations in an aqueous solution is presented. The sensor consists of three CSRR cells engraved on the bottom level of a 59 mm x 20 mm x 0.8 mm FR4 (εr=4.3) dielectric substrate with a sensing area of 36 x 20 mm2. The cells operate over the 2.3 - 2.4 GHz band and are powered by a 50 Ω microstrip waveguide at the bottom of the substrate. A sensitivity analysis, starting from an optimization of the thickness of the glass layer added to the cells to avoid short circuits between the sample solution and the CSRRs rings, is performed. The sensitivity analysis is carried out by varying the concentration of glucose in the range of 40-150 mg/dl dissolved in aqueous solution. The simulations performed by 3D CST Studio Suite 2021 with an optimum value of the glass layer thickness of 10 µm and a 38 x 20 mm2 area show a sensitivity value equal to 5.72 MHz/mg/dl which represents the highest sensitivity value compared to previously published works

Microwave gas sensor based on graphene aerogels

In this article, the experimental demonstration of a novel microwave gas sensor based on graphene aerogel is presented. This device makes use of a highly porous structure of the aerogel in combination with the modulation of graphene AC conductivity upon exposure to vacuum and ambient air. As a proof of concept, we integrate the graphene aerogel into rectangular waveguides and measure its scattering parameters by a Vector network Analyzer (VNA). The aerogel is characterized by a combination of scanning electron microscopy and four-probe DC measurements. The aerogel is integrated into WR-90 waveguides by custom-designed support and wave propagation is tested over the 8-12 GHz frequency range (Xband). By exposing the aerogel to either air or a moderate vacuum, clear shifts in the waveguide scattering parameters are observed. In particular, changes of ≈ 3 dB and ≈ 1 dB in the transmission and reflection parameters of the waveguide are obtained, respectively. Moreover, the sensor exhibits excellent reproducibility when exposed to alternating cycles of air and vacuum, proving that the shifts in microwave transmission and reflection are caused by changes in the conductivity of the graphene aerogel due to the absorption and desorption of gas molecules. These proof-of-concept results pave the way for the development of a new class of gas sensors for applications such as breath analysis