Research On High-density Pressure Sensing System Based On Fiber Bragg Grating

Intelligent monitoring technology is of great significance for the large and complex engineering structures,especially,in long-term,high reliability monitoring.Pressure sensing is an important part of the intelligent structural health monitoring technology.In the process of structure maintenance,finding out the location of bad load quickly and accurately is extremely important to improve the service life of large structures.With the development of optical fiber sensing technology,the FBG sensors can replace the traditional electrical sensors.Fiber Bragg grating(FBG)has the unique advantages of small size,light weight,anti-electromagnetic interference,high resolution and easy to form a distributed monitoring network.So it is widely used in structural health monitoring research fields,such as aerospace,industrial manufacturing,medical devices,civil engineering,etc.This work has developed a high-density pressure sensing unit of an area of 1cm~2printed by resin C-UV 9400E based on the sensing principle of FBG.This unit is divided into nine regions averagely and nine fiber Bragg grating sensors(FBGs)are embedded vertically.The main contents of this dissertation are as follows:1.The strain sensing model and temperature sensing model of FBG sensor are analyzed,and the three parameters of grating length,temperature and strain are simulated.The relative error between strain simulation results and theoretical values is 1.639%.Then the cross-sensitivity of force and temperature is briefly analyzed,and several common multiplexing techniques and demodulation methods are introduced.2.Set up a pressure system to force on the pressure sensing unit.By measuring the FBGs'wavelength shifts,the sensing unit can detect the loading location.A number of experiments have been carried out to perceive the pressure fluctuation and test the position symmetry by loading on the No.1,2 and 5 locations with a range from 0?10N.The phenomena of finite element simulation are consistent with the experimental phenomena.The experimental results show that the FBGs'wavelength shifts on the loading location are larger than them on the other locations.The average linear correlation coefficient of the FBGs'response is 0.9981.Two groups of position symmetry experiment on No.1 location indicate that the ratios of the sensitivity are1.022 and 0.78,respectively.Calibrate the pressure of nine FBGs,and the average linear correlation coefficient is 0.9978.3.Build the hardware system of nine-channel FBG pressure demodulation.According to the system design scheme,select the appropriate device to complete the construction of the whole hardware system.The principle and function of each device in the demodulation system are introduced in detail,and the connection scheme of the optical switchs is explained.4.Design the user interface of the pressure demodulation system through LabVIEW software.The user interface includes a login interface and an operation interface.The whole demodulation system can be controlled by the operation interface,and the monitoring value can be displayed on the operation interface.The test results show that the average relative error of the central wavelength data between the pressure demodulation system and the fiber Bragg grating demodulation is 0.082%.When loading on the No.2 and 7 locations,the average relative error between the monitoring value and the actual value is 5.428%and 4.893%respectively,the average deviation is 0.22N and 0.2N respectively,and the standard deviation of the monitoring force value is 0.09N and 0.06N respectively.The demodulation system is easy to operate with a high-precision monitoring function and practical application value.5.The remote monitoring terminal of the pressure demodulation system is designed based on the communicating between the host computer and the GRMOPC wireless communication device.The whole pressure demodulation system can be monitored in real time on the mobile phone APP monitoring interface and the computer web monitoring interface.The remote monitoring system also has the functions of short message reading,short message control and short message alarm.Finally,the dissertation summarizes the research results and shortcomings,puts forward some suggestions for the future research work.