A design of an ultra-compact infrared gas sensor for respiratory quotient (qCO2) detection

[Display omitted] •The minimum size of the sensor is only 10% of the conventional NDIR gas sensors’ with the same gas detection resolution.•A new structure of gas-cell was designed with high coupling efficiency (61 %).•The sensor is characterized by simulation and experimental analysis.•The sensor's limit of the detection range is 0–20 % with ±30 ppm of the accuracy. We present an integrated non-dispersive infrared (NDIR) gas sensor for respiratory quotient (qCO2) detection with ultra-compact size and low-power consumption. The NDIR gas sensor consists of a MEMS emitter with broadband radiation, a special designed gas-cell with high optical coupling efficiency, and a MEMS thermopile detector. The minimum size of the sensor is 10 mm × 10 mm × 4 mm (length × width × height) which is only 10 % of the size of conventional NDIR gas sensors with the same gas detection resolution of around 65 ppm. The sensor is suitable for detecting gas (e.g. CO2) with concentrations in the range of 0.5 – 20 %. This sensor has potentials to be adopted by portable breath analyzers and indoor air quality monitoring systems, etc.