A gas sensor using double split-ring resonator coated with conducting polymer at microwave frequncies

In this research, a gas sensor using double split-ring resonator (DSRR) incorporated with conducting polymer (CP) is proposed at microwave frequencies (K_u-band). The DSRR fabricated on printed circuit board (PCB) is excited by a high-impedance microstrip line, and the CP is coated inside of an inner circle of the DSRR. Electrical characteristics of the CP can be deviated by an interaction between CP and a target gas, and then this deviation of electrical characteristic is demonstrated by S21 frequency response of the DSRR. To examine the performance of the proposed sensor, 100 ppm ethanol (C₂H₅OH) gas is exposed at room temperature. According to the measured result, the S₂₁ resonance frequency of the DSRR is shifted by 220 MHz and simultaneously, the resonance amplitude is changed by 0.79 dB level. It is clearly found that the DSRR with CP material can be a good candidate for a sensitive gas sensor operating at microwave frequencies.