Key Technology Research Of Outdoor PM 2.5 Concentration Detection System Based On Fiber Optic Sensing

In recent years,with the rapid development of China's economy and society,haze phenomenon occurs frequently.The culprit is PM_2.5,which seriously affects the air quality and has great harm to human health.Therefore,it is very important to detect the concentration of outdoor PM_2.5 in real time.Optical fiber sensor has been widely used for lots of advantages,such as high sensitivity,corrosion resistance,low insertion loss,anti-electromagnetic interference,not affected by nonlinear effects,can be used in distributed measurement,and it has become one of the most important devices in the field of optical communication and sensing.However,the real-time detection of outdoor PM_2.5 concentration based on optical fiber sensing has not been studied in detail.The main innovation and research contents of this paper are as follows:?1?The structure of sampled fiber grating has been studied in this paper and the theoretical studies of reflective spectrum characteristics of sampled fiber grating has been carried out.By using the transfer matrix method,the theoretical model and mathematical expression of transmittance and reflectance of sampled fiber grating structure have been derived.The numerical simulation experiment has been carried out in MATLAB software platform.The effect on the reflective spectrum characteristics of the sampled fiber grating length L,the sampled period P,refractive index modulation strength and duty ratio T have been studied and analyzed in detail.The simulation results show that when duty ratio T=0.1,the comb spectrum characteristics of sampled fiber grating is ideal,and its reflection peak is even close to 1,side-lobe interference is small as well.?2?Based the transfer matrix method and choosing proper parameters,cross-sensitivity of temperature and strain in sampled fiber grating sensor has been studied and a new cross-sensitive temperature-strain sensor based on sampled fiber grating is designed.Its temperature measurement range is from-50 to 200? with strain test range from 0 to 2000 ??.Using OptiGrating software,simulation experiments are carried out.The sensing performances of temperature and strain are obtained.Based on combination of the temperature and strain,utilizing SPSS software and the method of linear regression analyses,the dual-parameter matrix equations are provided.Four sensing coefficients,A,B,C and D,are calibrated with the values of-0.000337/??,-0.000115/?,-0.000545nm/??,and 0.012806nm/?,respectively.The study's results show that it can simultaneous test both temperature and strain through the measurements of reflectivity change value and wavelength shift of sampled fiber grating spectrum.It only uses a piece of sampled fiber grating and needs one set of demodulation system.In addition,due to the low cost and ease to fabricate and integration,our design is anticipated to have good potential applications in certain circumstances.?3?Based on the above two points,aimed at the disadvantage of poor real-time performance in the method of filter membrane weighing,combined with the standard of national ambient air monitoring,a real-time outdoor PM_2.5 concentration detection system based on optical fiber sensor has been designed,it can be used for the measurement of 1 hour average concentration values and daily average concentration for atmospheric fine particles(PM_2.5).According to the function of the detection system,the whole system is divided into four functional modules,and then the function,workflow and implementation of each function module were described.At the same time,the simulation of the system monitoring interface is carried out on the MATLAB software platform.Finally,the in-depth study and analysis for the error of the detection system has been carried out.The possible errors of the system are described in detail,and the improvement methods are given.