Gas sensing, as a typical application in intelligent systems, is receiving increasing attention in both industry and academia. It has widespread and common applicationsin the areas such as: industrial production (e.g., methane detection in mines); automotive industry (e.g., detection of polluting gases from vehicles); medical applications (e.g., electronic nosessimulating the human olfactory system); indoor air quality supervision (e.g., detection of carbon monoxide); and environmental studies (e.g., greenhouse gas monitoring). Recently much effort has been made to improve traditional metal oxide gas sensors and also to design new gas sensor structures. The extremely high surface-to-volume ratio and hollow structure of nanomaterialsis ideal for gas molecules adsorption. Therefore, gas sensors based onnanomaterials, such as carbon nanotubes (CNTs), nanowires, nanofibers, and nanoparticleshave been investigated widely. On the other hand studies show that metal oxide material modified by nanostructures has significant gas sensing properties. This study with the main purpose of methane detection isdivided in two sections. In the first section, the sensitivity enhancement of tin oxide gas sensor as one the popular gas sensorsbyusing carbon nanotube and silver nanocluster is investigated theoretically and experimentally. Also it is aimed to find an electrical circuit model based on obtained results. In the second section, study and simulation of carbon nanotube as one of the new attractive materials in gas sensor designs is investigated. Quantum Espresso software is used for simulations. Through the simulations the effect of gas molecule (O 2 , H 2 and CH 4 ) adsorption on electrical properties of (8,0) SWCNTis investigated. Also the effect of metallic atoms (Rh, Ni, Ag) adsorption on CNT surface in methane detection is examined. After finding the best additive, thin film structure of metal decorated CNTis fabricated and experimental results are compared with simulation results. Keywords Gas sensor, Tin oxide, Carbon nanotube, Silver nanoparticle, Modeling, Density functional theory
