Research On Optical Fiber Sensor For Water Dissolved Oxygen Measurement

The dissolved oxygen content in seawater reflects the current water quality of eawater and is one of the important indicators of seawater self-purification capacity.How to quickly and acuurately measure the dissolved oxygen content in seawater has attracterd more and more researcher's attention.Nowadays,the methods for real-time online measurement of dissolved oxygen sensor have their own characteristics,the dissolved oxygen sensor based on optical method has the charateristics of fast response time,no electromagnetic interference,low transmission and no oxygen consuming during the measurement process.The type of sensor has become the exploration direction of a new generation of dissolved oxygen detection technology.In the parper,two fiber optical fiber sensors based on optical methods for detecting dissolved oxygen sensor are proposed.One is dissolved oxygen based on the principle of fluorescence quenching,which measures the dissolved oxygen content by measuring the fluorescence intensity.The other is based on the principle of surface plasmon resonance.The dissolved oxygen sensor is made by modifing a oxygen-sensitive hemoglobin on the surface of the fiber SPR sensor.The sensing performance of the two sensors measured and analyzed separately.The main work of this thesis includes:(1)A fluorescent fiber sensor based on the principle of fluorescence quenching was designed.Ru(bpy)2Cl2 was selected as a the oxygen-sensitive fluorescent material We measureed its fluorescence characteristics and obtained the excitation wavelength and the emission wavelength.The sensing model of the fiber optic probe was established and the optimal structural parameters of the structure were simulated.A fluorescent fiber sensor was prepared by coating a fluorescent material on the surface of the fiber using a layer-by-layer selfassembly technique.(2)The method of detecting the fluorescence intensity was used to measure the dissolved oxygen content,and an experimental system for measuring the dissolved oxygen concentration was constructed.The sensor's sensing characteristics were tested after building a complete experimental system.The experimental results showed that the sensor had a good linear response in the range of dissolved oxygen concentration from 5mg/L to 15mg/L.By the fitting of the S-V equation,the coefficient of the constant KSV was found to be 0.15.Subsequently,the reversibility,response time and temperature effects of the dissolved oxygen sensor were analyzed,and the repeatability of the sensor was studied.Finally,the comparison and analysis of the sensing characteristics of the step structure and the thin cone structure were carried out.(3)A dissolved oxygen sensor based on the modified optical fiber SPR principle of modified hemoglobin was designed.Based on the theoretical basis of fiber surface plasmon resonance,a reflective fiber optic SPR sensor model was designed.The structural parameters such as the core diameter of the sensor,the length of the sensing area and the thickness of the gold film were simulated and analyzed.The optimal value of the structural parameters.The sensor was fabricated based on the structural parameters obtained from the simulation results.A reflective optical fiber SPR sensor was fabricated by vacuum coating.The refractive index sensitivity of the reflective SPR sensor was then tested.(4)Hemoglobin was modified on the surface of the gold film,and measurement of dissolved oxygen was performed.The experimental results showed that the detection sensitivity of the sensor in the dissolved oxygen concentration range of 2mg/L?20mg/L was 3.271nm/mg·L-1,and the minimum detection limit was 0.03mg/L.Subsequently,the repeatability of the sensor was also experimentally studied,which proved that the sensor can be used for repeatability measurement.Finally,a silver film SPR sensor was used to measure the sensitivity of the refractive index and compared it with the refractive index sensitivity of the gold film.After analysis and comparison,hemoglobin was modified on the surface of the silver film,and the dissolved oxygen concentration was measured.The experimental results were analyzed.Finally,the modification of the carbon nanotube tube material on the surface of the gold film enhances the sensitivity of SPR,thereby improving the sensitivity of the dissolved oxygen concentration detection.