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
$(S_{21})$
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.