Novel gaseous phase ethanol sensor implemented with underloaded RF resonator for sensor-embedded passive chipless rfids

This paper presents a novel gaseous phase ethanol resonant sensor implemented with underloaded LC-resonator. The device exhibits large variations in S₁₁ and Group Delay under ethanol exposures. By operating the OV-225 and OV-275 polymer-coated chemi-capacitors at RF frequencies, the E-field confined around the conductor surface sees a maximized polymer exposure surface, thereby improving both the response time and sensitivity. Under exposures of various ethanol concentrations, the OV-225 sensor showed a transient response time constant of ~60s, an frequency shift of 24.5MHz, and respective S₁₁ and Group Delay sensitivities of 3.12e-2 mdB/ppm and 9.49e-2 ps/ppm across the 0-5000ppm ethanol concentration span; the OV-275 version exhibited transient time constant of ~30s, a frequency shift of 22.5MHz, an S₁₁ and Group Delay sensitivities of 3.71e-1 mdB/ppm and 1.94 e-1 ps/ppm, respectively.