Miniaturized photoacoustic CO2 gas sensors - A new approach for the automotive sector

After the ban of R134a as a coolant for mobile applications and the dispute about R1234yf as its replacement, R744 as CO2 takes over an important role as an alternative and effective medium to transport the energy in air conditioning systems. Due to safety issues resulting from this change of medium as well as from the growing consciousness about air quality in the interior of vehicles, there is a rising demand for miniaturized and reliable CO2 sensors within the automotive market. The non-resonant, closed, photoacoustic system (PAS) which is presented in this paper is based on two chambers within a ceramic housing. The present system is a concept which carries potential in the areas of miniaturization and cost efficiency. The main aspects are the reduction of absorption distances to a minimal amount and a reliable system set up. Those aspects can be achieved by combining both a thermal MEMS-infrared emitter and a MEMS-microphone adapted to photoacoustics, which are each housed in a hermetically sealed ceramic enclosure. The sensor has been assembled in a measurement system and systematic measurements to characterize the system behaviour have been conducted.