Radiowave technology of resonant gas-sensor microwave telemetry

The possibility of using microstrip reflector microwave resonators in solving problems of resonant gas-sensor telemetry on layered dielectric substrates with gas-sensitive sputtering was investigated. It is noted that the use of chemically active sputtering, for example, on the basis of zeolites having a high selective gas adsorbent kinetics in terms of speed, makes it possible to create radiosensor materials capable of changing the dielectric constant in the process of absorbing gases, as well as of sublimated vapors of solid and liquid phases of various compounds. As an alternative approach in the field of dosimetric gas monitoring, a modification of radiosensor applications based on microwave sensors is proposed, which allows using microwave solutions based on microstrip microwave resonators with active gas-sensitive sorption zeolite sputtering on a dielectric substrate to conduct gas analysis in real time. The radio-wave principle of the microstrip gas sensor analyzer was formulated. An electrodynamic model of a microstrip gas sensor analyzer in the Altair Feko environment was developed. An experiment was planned, and gas-sensor telemetry tests of ammonia vapors  dissolved  in  water were carried out. It was established that the amount  of sorbed water and ammonia in the zeolite unambiguously conforms both to the absolute value of the reflection coefficient at resonance and to the resonant frequency itself. Using  the example of recording hydrogen nitride vapors it was shown that the reflection coefficient and frequency shift in the resonator, which depend on the concentration of the adsorbed gas, correspond to the saturation characteristics of the gas sensor and make it possible to repeatedly measure small concentrations of a gas that can be absorbed by zeolite at a temperature corresponding to the condition of rapid evaporation of controlled gas from the active dielectric layer, which guarantees desorption of the sensor. It was established that in order to increase the speed of the gas sensor response it is advisable to create a microstrip resonator for the resonance region of 8...10 GHz and to use a microstrip sensor substrate material with a high dielectric constant. This is due to the fact that the transition to the upper microwave frequencies will allow reducing the size of the topology of the microstrip resonator and reducing the effective area of the zeolite deposition, and, consequently, increasing the adsorption rate of the gas-sensitive layer of the active dielectric.

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