Design and Characterization of Macroscopic Indirect Photoacoustic Gas Sensor

A macroscopic photoacoustic gas sensing (PAS) system, along with the design considerations, are presented in this paper. The system is based on the indirect PAS principle. The system consists of a black body IR emitter, suitable optical windows for radiation transmission and a highly sensitive detector in the form of a microphone. A first prototype and its optimized version, for the CO2 PAS measurements, are subsequently developed and characterized. The prototypes are used for CO2 concentration measurements in the range of 0–5000 ppm. The length of the whole system is 8–15 cm, with the length of the variable measurement volume 5–12 cm. With the 5 cm long measurement volume, 10 ppm resolution is achieved for the second prototype. With the lock-in integration time of 307 seconds, the theoretical limit of detection (LOD) of 37 ppb is achieved.