Optimized Study Of Optical Fiber Ultrasonic Displacement Sensor System Based On Multimode Interference

With the progress of technology and the promotion of urbanization,the civil and transportation industry has been developing vigorously.In order to meet the regional connection and solve the problem of traffic jam,the quantity of bridge is increasing day by day,and a large number of Bridges have been built.The structure and function of bridge is more and more complex,which bears the responsibility of regional economic growth.However,as a fundamental task crucial for generations to come,the service life of the bridge has been decades or even centuries,and the load conditions are extremely complicated,such as wind load,temperature,vehicle load and earthquake load.Its security is tested by the environment.In order to ensure the safety,durability and applicability of the bridge,it is very important to build an economical and effective monitoring system of bridge displacement.It can provide timely feedback on the security situation of bridges,warning of impending disaster and prevent loss of life and property.In view of the limitations of existing bridge displacement monitoring system,this paper has developed a new bridge displacement monitoring system,which has important engineering practical value and economic significance.This paper first analyzes the research background and significance of bridge displacement monitoring.Through the comparison of the bridge displacement monitoring technology,optical fiber sensor technology and ultrasonic ranging technology at present,this paper summarizes the limitations of bridge displacement monitoring technology and provides a reference.Secondly,for suitability requirements of bridge monitoring system,this paper proposes an optical fiber ultrasonic sensor system based on multimode interference for bridge three-dimensional displacement non-contact monitoring.The optimization design of optical fiber sensor packaging material and optimization design of sensor structure are carried out.Finally,for the requirement of high precision three-dimensional displacement monitoring requirements,this paper carries out the sensor system experiment research of temperature and humidity factors and its error correction method,mechanism,models,systems theory and experimental research of optical fiber ultrasonic sensor system,the feasibility analysis of three dimensional sensor system based on diagonal displacement sensor,the simplified three dimensional displacement sensing experiment,simulation experiment of bridge displacement monitoring.The main research contents of this paper include:1.This paper analyzes the present situation of the existing bridge displacement monitoring technology to compare the advantages and disadvantages and scope of use,and summarizes the limitations of current bridge displacement monitoring technology.In this paper,the research status of fiber optic sensors and ultrasonic distance measuring technology is investigated,and a fiber sensor system based on high elastic diaphragm is proposed to monitor the three-dimensional displacement of bridge.2.This paper studies the sensor diaphragm material properties optimization technique.The influence of elastic modulus and Poisson ratio on sensor sensitivity is analyzed.Combined with the experimental results of 25 kHz continuous ultrasonic detection,this paper has verified that the optimization of material properties can effectively improve the sensitivity of optical fiber sensors to high frequency ultrasound.In this paper,the optimization technology of diaphragm structure is studied.By using ABAQUS software to analyze steady displacement of high elastic vibration membrane,this paper establishes the sensor diaphragm thickness effect on the sensitivity.Combined with ultrasonic detection experiment,this paper proves the feasibility of improving sensor sensitivity by optimizing sensor structure.On the basis of this,this paper obtains the relatively optimal high elastic diaphragm structure(10mm diameter and 0.25 mm thickness)through finite element simulation and experimental study.After material and structure optimization,the sensitivity of the sensor by the original 63.2 mV increased to 326.1 mV,non-contact detection range increased from the original 7 m to 15 m,which effectively improve the response sensitivity and response intensity of the optical fiber sensor.The realization of the non-contact displacement sensor system detection distance is greatly increased.3.By establishing fiber ultrasonic displacement sensor system based on multimode Interference and the displacement sensing experiment,the feasibility of the high precision of the optical fiber ultrasonic displacement sensor system is verified.On the basis of this,this paper carries on the study of the influence of temperature and humidity environmental factors,and conducts experimental research on the stability of the system by environmental crosstalk experiment.This paper gets an affect how temperature and humidity influence the accuracy of the system.Based on the analysis of experimental results,this paper establishes the method of temperature and humidity error correction.The experimental results show that the maximum error of the sensor system after modification is reduced from 4.8% to 3.46%.4.This paper proposes a three-dimensional displacement sensing method based on spatial analysis and its theoretical model.Through ultrasonic pulse signal detection experiment and oblique displacement sensing experiment,the feasibility of establishing three-dimensional displacement sensing experiment is verified.In this paper,a simplified three-dimensional displacement sensing exploratory experiment is carried out.The research results show that when the system in X axis and Y axis and Z axis has 3 mm displacement at the same time,the maximum error is 0.18 mm;the relative error is 6%.This can realize the three-dimensional displacement sensor's high precision.5.The general rule and characteristics of bridge displacement change are studied.In the experiment,the single direction large displacement,single direction small displacement and three-dimensional displacement of the bridge under different stages are simulated.The maximum relative error of the designed sensor system was 3.28%.In this paper,the non-contact displacement simulation monitoring of the large deflection in the early completion of the bridge,the small deflection in the post completion period and the three-dimensional displacement of the bridge during the operation period of the bridge is preliminarily realized by the optical fiber ultrasonic three-dimensional sensor system.It is proved that the optical fiber ultrasonic three-dimensional displacement sensor system can measure the single direction large displacement,the single direction small displacement and the three-dimensional displacement in high precision.The experiment provides the experimental basis and theoretical basis for the actual bridge displacement monitoring.