Passive Coupled Microwave Resonators for VOC Monitoring Using Flexible PDMS Beam

Microwave monitoring methods are promising gas/polymer interaction monitoring tools. This paper outlines a microwave investigation into the interaction between a polydimethylsiloxane flexible (PDMS)-coated split ring resonator (SRR) and a volatile organic compound (VOC) using a reader SRR. The SRR, resonating at ~~2.6 GHz, was mounted on an RT5880 Rogers substrate with a thickness of 0.51mm, backed by a ground plane. When Tetrahydrofuran (THF) was exposed, the PDMS-coated SRR interacted with the gas molecules and underwent a swelling phenomenon. This physical swelling, significantly impacted the PDMS structure, leading to a vertical deflection of the PDMS-coated SRR beam and altering the resonant profile (S21) properties of the coupled microwave resonators. The experimental findings revealed that when subjected to VOC concentrations in the range of 1–3 ml Tetrahydrofuran in the chamber, the sensor exhibited a 40 MHz shift in the resonant frequency and a 30 dB change in the resonant amplitude. This finding underscores the potential of this detector for VOC monitoring and, notably, opens an avenue for in-depth exploration of the interaction between polymers and gases.