Microwave Gas Sensor Based on Graphene Aerogels
Yang Wu, Gabriele Restifo Pecorella, Gianluca Verderame, Daniele Annicchiarico, Thanuja Galhena, S.A. Hodge, Hannah J. Joyce, Patrizia Livreri, Antonio Lombardo
Abstract
In this article, the experimental demonstration of a novel microwave gas sensor based on graphene aerogel (GA) 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 GA into rectangular waveguides and measure its scattering parameters with a vector network analyzer (VNA). The aerogel is characterized by a combination of scanning electron microscopy (SEM) 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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band). By exposing the aerogel to either air or a moderate vacuum, clear shifts in the waveguide scattering parameters are observed. In particular, changes of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\approx } {3}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\approx } {1}$ </tex-math></inline-formula> 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 GA 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.