Six-port microwave system for volatile organic compounds detection

An interdigital capacitor with resonant frequency fres N 8.6 GHz 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 0-25 ppm concentration range. The measurement system has been significantly simplified due to measurement of the reflection coefficient at a single frequency f(o) = 8 GHz, 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. (C) 2017 Elsevier B.V. All rights reserved.