Microwave gas sensing with a microstrip interDigital capacitor: Detection of NH3 with TiO2 nanoparticles

This work presents new developments in the microwave transduction and its application to gas sensors. Microwave measurements were extended to reflection/transmission coefficients through the use of a microstrip interdigital capacitor design. A sensitive layer composed of commercial TiO2 nanoparticles was deposited on the sensor surface, in order to detect the ammonia target gas. A complete analysis methodology is proposed. It allows to identify without ambiguity all the sensor frequencies of interest, as well as a full characterization of usual gas sensor parameters such as reproducibility, stability, response time, etc. Furthermore, it involves a new method of representation which significantly limits the amount of unexploited data collected during microwave measurements. The proposed sensor exhibits a strong correlation between response values and injected ammonia concentration between 100 and 500 ppm, with a good reversibility and stability of the measure.