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.