Microstrip Spiral Resonator For Microwave-Based Gas Sensing

This paper presents the design of a new microstrip gas sensor based on a trapezoidal spiral resonator covered by a titanium dioxide nanoparticle layer. Reflection and transmission coefficient measurements between 1 and 8GHz revealed multiple resonances that can be used in the context of gas detection. The sensor response upon ammonia adsorption has been evaluated on the whole frequency span with a simple spectral analysis. Kinetic parameters such as response time, reversibility, and measurement stability have been determined with a monofrequential temporal analysis. The sensor showed at each resonance a good sensitivity to ammonia for concentrations between 50 and 300ppm, with a response time less than 1 min. The maximal response was reported at 7.76GHz with a reflection coefficient variation of 0.45dB after the injection of 300ppm of ammonia, which is 3.5 times higher than previously reported.