Development of a MEMS hotplate-based photoacoustic CO2 sensor

Instead of the conventional use of micro-electro-mechanical system (MEMS) hotplate for metal oxide semiconductor (MOS) or nondispersive infrared (NDIR) gas sensing, it was used for photoacoustic (PA) gas sensing. A low-cost MEMS microphone was used for the development of this MEMS hotplate PA carbon dioxide (CO₂) sensor. To the knowledge of the authors, this is the first time that a MEMS hotplate and a MEMS microphone are combined for use in gas sensing with high modulation frequency. NDIR sensors use much more expensive photodetectors compared to the MEMS microphone used in this work. The MEMS hotplate and MEMS microphone have the desired characteristics of low power consumption, small size and low cost. The hotplate as a blackbody is a good infrared emitter which is suitable for CO₂ detection around the 4.26 µm absorption band. Despite the significant radiation power loss due to high modulation frequency, the remaining/reduced power radiation power was still sufficient to excite CO₂ molecules for PA signal generation. Temperature analysis on the sensor showed that PA signal decreases with an increase in temperature, which implies that compensation must be provided for such temperature effects. This work provides alternative optical gas sensing that is comparatively inexpensive compared to the conventional NDIR sensors and by using components that can be easily mass-produced, thereby making a valuable contribution to the fight against air pollution and global warming.