Research On Sensor For Sensing Dissolved Oxygen In Seawater Based On Fluorescence Quenching

Dissolved oxygen is a significant parameter of seawater quality and a key index of marine pollution monitoring.Although chemical and electrochemical methods are traditional techniques to measure the concentration of oxygen dissolved in water,these two techniques have shortcomings such as long response time and oxygen consumption.The dissolved oxygen sensor based on fluorescence method makes up for the shortcomings of traditional methods,and has the characteristics of high precision,high real-time performance and low power consumption.According to the actual demand of Marine water quality detection,the theory of detecting dissolved oxygen concentration in seawater by fluorescence method is deeply analyzed.And a research design for dissolved oxygen sensors based on fluorescence lifetime is determined.In order to achieve real-time and precise measurement of dissolved oxygen concentration in seawater,the following research has been carried out.Firstly,the research status of dissolved oxygen content measurement technology based on fluorescence method at home and abroad is investigated,and the feasibility of measuring dissolved oxygen concentration based on fluorescence quenching principle is determined.Secondly,the ideal excitation wavelength and fluorescence center wavelength are determined by analyzing the three-dimensional fluorescence spectrum of the fluorescence sensing film.Simulated analysis is done on the light distribution after the addition of an optical waveguide.Based on this,the optical path structure of the sensor probe is designed,which supports the subsequent transmission and conversion of optical signal.Thirdly,the influence of the sensing system’s modulation frequency on the sensor’s performance is studied,and the DDS signal generator is built with FPGA to complete the modulation of the signal.Light source driver circuits,photodetector driver circuits,and phase-locked amplifier circuits are designed to complete the signal conversion.FPGA is used to drive DAC and ADC chip to complete signal conversion and signal acquisition,and the serial port is used to interface with the host computer.Finally,the phase shift of the dissolved oxygen sensor under different modulation frequencies is tested experimentally,and the best modulation frequency is obtained by analyzing the experimental data.The linear relation function between the output result and the concentration of dissolved oxygen is established by fitting the characteristic curve of the output of dissolved oxygen sensor.Experimental analyses of the sensor’s performance characteristics and the study of how other factors in seawater affect the sensor are conducted.This paper provides theoretical basis and experimental guidance for measuring the concentration of dissolved oxygen in seawater.