An mmWave Sensor for Real-Time Monitoring of Gases Based on Real Refractive Index

We propose a millimeter-wave (mmWave) sensor to monitor gases and aerosols based on time-of-flight (ToF), thus, on the real refractive index. It utilizes an ultrawideband frequency-modulated continuous-wave (FMCW) radar operating from 72 to 92 GHz at a sampling rate of 500 Hz. Also, we introduce a model for simulation of the refractive index of arbitrary gases at mmWave frequencies using molecular spectroscopic data. Simulations then allow the identification of the respective gas under test. We characterized the performance of the sensor regarding the refractive index within various experiments. The precision is 0.027 ppm, and the 20-h long-term stability is better than 0.2 ppm. The linearity is at least 1.5 ppm. Due to sophisticated temperature compensation, the temperature drift is less than 10 ppm for 30 K. Since the sensor is accurate, precise, and robust, it is perfect for in-process real-time monitoring and classification of gases or aerosols in the industry.