Research On Fiber Methane Gas Sensing Based On SPR Sensing

Methane,as one of the air pollution gases,is flammable and explosive,which seriously threatens human life and property.Real-time monitoring of methane concentration is of great research value to improve the air quality of living environment and eliminate safety hazards.Sensitive materials coating fiber surface plasma resonance（SPR）sensor has many advantages such as anti-electromagnetic interference,electrical insulation,corrosion resistance,multi-point multiplexing and so on.It is extensively used in the field of industrial gas on-line monitoring,harmful gas composition analysis,air quality monitoring and so on.This thesis focuses on the fiber SPR sensor coated with methane gas sensitive material,and carries out the following work:Firstly,the research purpose and significance of fiber SPR methane gas sensor are described.The research status of methane gas sensors at home and abroad is summarized,and the existing disadvantages of methane gas sensors are analyzed.Based on SPR technology,a methane-sensitive fiber optic sensor is proposed to improve the response sensitivity and selectivity of the methane sensor.In addition,the working principle of fiber surface plasmon resonance methane sensor is introduced.The factors affecting the performance of the methane sensor and the parameters of evaluating the performance of the sensor are analyzed in detail.Secondly,using the finite element method,this thesis tries to simulate the response characteristics of optical fiber SPR sensor with the different parameters of the fiber core-clad-metal-sensitive material type,and the parameters such as the type and thickness of coating material,the length of sensing area are optimized.Besides,the sensor performance is evaluated from several aspects,such as sensitivity,transmission depth and quality factor（FOM）.The results show that in the range of methane concentration from 0 to 3.5%,when the fiber core diameter is 10μm,the cladding diameter is 11μm,and the thickness of Ag layer is 20 nm,the methane concentration response sensitivity of the sensor can reach-3.51 pm/ppm.When the core diameter is 10μm,the cladding diameter is 11μm,and the Au film thickness is 10 nm,the methane concentration response sensitivity of the sensor can reach-3.14 pm/ppm.Finally,the experiment studies the effects of coating metal type,thickness and sensing region length on the performance of sensor,and the optical fiber SPR sensing structure with Cr/Au double-layer coating metal is established.When the thickness of bimetallic Cr/Au metal layer is 10/50 nm and the sensing region length is 15 mm,the sensor sensitivity and stability are the best.Pd-SnO₂/rGO gas sensitive materials are prepared by hydrothermal method.The crystal structure,microstructure and composition of the gas-sensitive material are analyzed by means of SEM,EDS and XRD.A Cr/Au bimetallic fiber SPR sensor coated with Pd-SnO₂/rGO and acupoint sensitive materials is designed and fabricated.The research studies the sensitivity,repeatability and selectivity of the sensor for methane gas concentration measurement.The results show that the response sensitivity of the sensor coated with Pd-SnO₂/rGO sensitive material is up to 1.02 pm/ppm.The sensitivity of the sensor coated with acupoint sensitive material can reach-0.55pm/ppm.It realizes the sensor measurement of methane gas with high selectivity and sensitivity and has good repeatability.To sum up,the combination of optical fiber SPR sensor and metal oxide gas sensitive material makes the sensor have the advantages of high sensitivity and strong selectivity,which provides an effective method for methane gas detection.