Six-port microwave system for volatile organic compounds detection

Abstract

An interdigital capacitor with resonant frequency fres ≈ 8.6GHz coated by comb polymer Pc-based thin film as a sensitive layer was investigated under exposure to different concentrations of various VOCs, such as: acetone, ethanol, methanol, isopropanol, butanol and ethylbenzene in a 0–25ppm concentration range. The measurement system has been significantly simplified due to measurement of the reflection coefficient at a single frequency f0=8GHz, at which the sensor exhibits the largest change in reflection coefficient's magnitude. For the reflection coefficient's measurement a new six-port reflectometer has been developed, which provides an enhanced measurement accuracy for the measurements of reflection coefficients having small magnitudes. The developed detector based on microwave measurements can be utilized in a portable exhaled breath analyzers.