Gas analyzer based on the microwave electrodynamic resonator

A gas analyzer based on an electrodynamic resonator made on a section of a rectangular waveguide is presented. On one side, the resonator was limited by a capacitive pin with an adjustable gap. The other side was loaded with a 0.5 mm thick lithium niobate plate onto which various gas-sensitive films were applied. The resonator is characterized by two resonances at frequencies of ~5.9 and 7.3 GHz, at which measurements were performed. One end of the waveguide containing a lithium niobate plate with a gas-sensitive film was located in a sealed chamber with the gas being studied. The other side of the resonator was connected to an S-parameter meter of the E5071C type, operating in the mode of measuring the frequency dependence of the reflection coefficient S11. A mixture of air and ammonia was used as the gas under study. The dependence of the reflection coefficient on the ammonia concentration was plotted for each resonance for all the gas-sensitive films under study. It was shown that when the ammonia concentration changed from 0 to 0.16%, the reflection coefficient changed within 33 – 50%. The resonance frequencies remained practically unchanged.