Photoacoustic CO2-Sensor for Automotive Applications

Towards Integrated Mid-Infrared Gas Sensors

“…A reference detector is often used to compensate for changes in the emitted light [40,48,53,54,58,59,64]. Additional sensors can be used to compensate for environmental parameters such as temperature, pressure or humidity [44,51,59,63,66]. In this section, we review the performance of current topologies with a focus on miniaturized devices, based on both acoustic and optical detection.…”

“…Because of their simplicity, and highly reliable performance, PA gas sensors are widely used. They have been implemented for a variety of gases, including: CO2 [15,51,68,69,80,81], CH4 [44,68,69,70,71,81], acetylene (C2H2) [68,82], ethane (C2H6) [68], CO [68,83], ethylene (C2H4) [68], C3H6O [67] sulfur dioxide (SO2) [67], NO [84], hexane (C6H14) [7], oxygen (O2) […”

“…Sensitive methods down to few ppb trace gas detection have been reported [7,66]. Various designs have been proposed, based on both resonant (R) (i.e., by tuning the emitter modulation frequency to an acoustic resonance of the cell, thus amplifying the sound signal) [7,66,67,70,71,72,81], and non-resonant (NR) cells [15,44,50,51,69,80,82,84], with light sources including LEDs [15,44,50,67,72], MEMS heaters [51,69,80], QCLs [84], interband cascade lasers (ICLs) [7,71], or DFBs [81,83]. Various strategies have been used to implement the acoustic detector, Table 2.…”

“…Various strategies have been used to implement the acoustic detector, Table 2. These include designs based on gas-filled [15,44,50,51,69,80,85], or unfilled MEMS microphones [66,67,71,72], optical microphones based on Fabry–Pérot interferometers (FPIs) [68,82], or quartz tuning forks (QTFs) [83,84]. Table 2 summarizes representative operation performances.…”

“…Gas sensors based on optical detectors, have been demonstrated for various applications (e.g., breath analysis [19,47], indoor air quality (IAQ) [48], or pollution control [49]). Photoacoustic sensors, using highly-sensitive MEMS microphones, have also emerged as compact, low-cost sensors with high sensitivity and stable operation [44,50,51]. Nevertheless, current optical gas sensing technologies still suffer from drawbacks, e.g., QCLs are expensive complex heterostructures [37,38], LEDs have limited emission for λ > 5 μm [39], and MEMS micro-heaters suffer from poor emissivity [52].…”