Development of a mid-infrared early fire detection system based on dual optical path nonresonant photoacoustic cell

A mid-infrared carbon dioxide (CO2) sensor system was developed for early fire detection based on photoacoustic spectroscopy. A miniaturized nonresonant photoacoustic gas cell was optimized by means of finite element method (FEM). A cylindrical cell was optimized with a radius of 12.7 mm and a length of 32 mm. An approximately proportional relationship between the optical path length and the amplitude of the photoacoustic signal was observed by theoretical analysis. The optimal modulation frequency was determined to be 44 Hz. A dual optical path was adopted to gain a low limit of detection (LoD) and a high sensitivity. The amplitude of the photoacoustic signal was increased by 1.8 times compared to single optical path. The LoD of the sensor system was measured to be 4.1 ppmv at an averaging time of 84 s.