| Quartz Enhanced Photoacoustic Spectroscopy（QEPAS）is a trace gas detection technology that utilizes a quartz tuning fork as the sensor core.It has lower cost,faster response,more compact results,and higher sensitivity in detecting special gases under precise environmental conditions.Carbon monoxide（CO）is a colorless and odorless harmful gas that is mostly generated from incomplete combustion of carbon-containing fuels.It poses great risks to human health and safety in many industrial production environments.In addition,modern medicine has pointed out that detecting CO produced by human metabolism is an important indicator for monitoring diseases.Therefore,a small,low-cost,high-sensitivity CO gas detector has significant importance in people’s daily production activities and health assessments.This thesis starts with the theory of gas molecule absorption and then sequentially introduces the QEPAS-related theories such as photoacoustic effect,photoacoustic spectroscopy,and piezoelectric effect.It describes the physical process in which the laser with wavelength periodic variation is absorbed by the absorption lines of the target gas spectrum in the gas environment,producing corresponding sound waves in the environment,and generating electrical signals in the piezoelectric material.The article focuses on calculating the energy accumulation method of the quartz tuning fork sensor,which is different from traditional photoacoustic spectroscopy technology,and introduces the wavelength modulation second harmonic detection technology used in the experiment.Secondly,based on the physical energy conversion process of QEPAS,the basic characteristics of the quartz tuning fork sensor were simulated using the finite element simulation software COMSOL.Variables such as laser incident position,detection pressure,and miniaturized gas chamber size were optimized.According to the simulation optimization results,a detection module with a 0.63m L quartz tuning fork sensor chamber was designed.Furthermore,a host computer integrated development of the detection and excitation signal control system was implemented using Lab VIEW,according to the detection parameters control and storage requirements.Then,according to the experimental requirements of pressure and different volume fractions of CO,a static gas configuration module that can configure different volume fractions and adjust gas pressure was designed.Finally,the simulation optimization was experimentally validated,and response signals for different concentrations of CO were measured.The relationship between the volume fraction of CO and the signal was calibrated,and the volume fraction detection limit of the sensor was calculated to be 531.2×10-9.The normalized noise equivalent absorption coefficient was 2.86×10-8cm-1W/Hz1/2.The detection results for various volume fractions of CO were statistically analyzed,and an average detection error of less than 0.8%was obtained.This thesis has designed,improved,and manufactured a high-sensitivity,small-sized standard CO-QEPAS sensor that can be applied to timely CO detection environments in casting,chemical industry production activities,or medical health assessments.This has reduced the cost of QEPAS gas detection equipment and achieved better detection limits and smaller measurement errors at the CO absorption line of6383.3 cm-1. |
