Carbon-nanotube loaded antenna-based ammonia gas sensor

Carbon nanotubes (CNTs) have been researched extensively for gas-sensing applications due to their unique electrical, chemical, and structural properties. Single-walled carbon nanotubes (SWNTs) have been predominantly used due to their superior electrical conductivity and higher sensitivity relative to multiwalled CNTs. This paper presents the design and characterization of a novel planar sensor fabricated on paper substrate to detect small concentrations of ammonia gas, using the shift in resonance frequency of a patch antenna as the discriminator. We have investigated three main design issues in depth. First, functionalization of the SWNTs with a polymer is studied in order to enhance the gas detection sensitivity. Second, a thin film of the functionalized SWNT is characterized to create a surface impedance model for the explanation and prediction of the resonance shift due to different gas concentrations. Finally, as a proof of concept, functionalized SWNTs are integrated into a patch antenna design and the return loss is measured in a closed-system environment to show high sensitivity for low concentrations of ammonia gas. The proposed antenna-based wireless gas sensor can be utilized in several applications, given its small form factor, light weight, and little to no power requirements.