An ultra-small integrated CO₂ infrared gas sensor for wearable end-tidal CO₂ monitoring

Human physiological metabolic status can be obtained by monitoring exhaled CO2 concentration, but current CO2 sensors have disadvantages such as large size, high power consumption, and slow response time, which limit their application in wearable devices and portable instruments. In this article, we report a small size, good performance, and large range CO2 infrared gas sensor that integrates a high emissivity MEMS emitter chip, a high detectivity thermopile chip, and a high coupling efficiency optical chamber to achieve high efficiency optical-thermal-electrical conversion. Compared with typical commercial sensors, the size of the sensor can be reduced by approximately 80% to only 10 mm 3 10 mm 3 6.5 mm, with the advantages of low power consumption and fast response speed. Further, a monitoring system for end-tidal CO2 concentration installed on a mask was developed using this sensor, and good results were achieved.