RESUMEN
We present a radio-frequency (RF) sensor and its measurement results of three volatile organic compounds (VOCs) at multiple frequency points from â¼ 2 to â¼ 11 GHz, which is a convenient range in our examination. The sensor is based on a simple RF interferometer and uses two coplanar waveguides (CPWs), A and B of 5 and 25 mm length, respectively, as VOC sensing electrodes. Approximately 70-nm-thick poly copolymer films are coated on CPW surfaces for VOC adsorption and concentration. It is shown that ethanol, acetone, and isopropyl (IPA) induce frequency-dependent RF responses, which are also VOC-dependent. Thus, the frequency-dependent properties provide a possible new approach for better VOC sensing selectivity. With CPW A, the limit-of-detections (LODs) are â¼ 600 ppm for ethanol, â¼ 270 ppm for acetone, and â¼ 330 ppm for IPA at 9.29 GHz. With CPW B, the LODs are roughly four times better. These LODs are also better than most of other RF VOC sensor results. In the future work, it is promising to further improve RF sensitivity and selectivity significantly.
RESUMEN
We propose to exploit filter stopband for high sensitivity radio frequency (RF) interferometer operation by utilizing reflection scattering parameters. Combined with passband filter operation, the modified RF interferometer effectively expands its frequency coverage. A simple model is described to analyze and predict interferometer performance. A high-pass filter and a low-pass filter are designed and built to demonstrate the interferometer operation as well as to verify the model over a frequency of 1-4 GHz. Lossy materials are shown to significantly degrade filter sensitivity enhancement effects due to reduced group delay and lower RF fields. Further work is needed to address the issue.