Fabrication And Characteristics Of Fiber Bragg Grating PH Sensor

For its good reinforcement effect and economic value,Prestressed anchor cable is widely used in engineering such as deep foundation excavation support,slope intensification,Tunnel support.However,corrosion is an important factor affecting the anchoring effect of prestressed anchor cable because of the existence of corrosive medium such as pH value of water,CO₂,Cl^-in the environment.The evaluating indication of cable corrosion detection method is single,which cannot truly reflect the corrosion status of anchor cable,so further research on the influence factors of cable corrosion is necessary.Existing pH detection method cannot be applied to detect the internal pH value of anchor cable for the factors such as narrow response range,measurement accuracy,limited application occasions and so on.Therefore,it is necessary to prepare a kind of sensor which can be used to detect the internal pH value of anchor cable.To meet the needs of the pH value detection inside anchor cable,the article put forward to make a pH sensor which is made of a single-layer pH-sensitive hydrogel coating FBG by combining technical advantages of fiber grating sensing and characteristics of pH-sensitive hydrogels,and tests the characteristics of the sensor according to the characteristics of the internal environment of the anchor cable and the performance requirements of the sensor.The main research contents are as follows:Firstly,it is known from analyzing the axial stress acting on FBG through relevant literature that the adhesion coefficient between hydrogel and FBG is also an important factor affecting the response sensitivity of fiber Bragg grating pH value sensor.Secondly,according to the characteristics of pH sensitive materials which applied to all kinds of pH sensors,HEMA-AA gel was chosen as the pH sensitive material of the sensor,and the gel was coated on FBG to make Fiber Bragg Grating pH sensor.In the pH range of 4-11,the sensitivity of the sensor is 0.025nm/pH,linearity is 0.997,and the function equation of the corresponding central wavelength can be expressed as Y=0.025*X+1540.089nm.Thirdly,by controlling the change of temperature,the temperature sensitivity coefficients of the sensor in pH 5,7 and 9 solutions are 0.0094nm/?,0.0095 nm/?,0.0096nm/?,and the temperature sensitivity coefficients of bare FBG is 0.01 nm/?.There is a few difference,and HEMA-AA hydrogel does not change the temperature characteristics of FBG.Fourthly,the oscillation behavior of the sensor between pH 5 and 9 was studied by controlling the pH value of the solution.According to the offset of the central wavelength of the sensor in the process of pH rising from 5 to 9 and pH dropping from9 to 5,it can be seen that the sensor has a certain degree of sustainability,and the response time of the sensor in the process of pH falling is longer.Fifthly,the stability and durability of the sensor are studied by controlling the change of dry and wet state of the environment.After several times of measurements and drying,the central wavelength of the sensor fluctuates up and down to 1540.07nm in both the measured state and the drying state,showing a certain stability.The pH response sensitivity of the sensor decreases from 0.025nm/pH to 0.004nm/pH,and the linearity decreases from 0.996 to 0.984 after 50 cycles of measurement and drying state.The durability can be indirectly improved by increasing the adhesion coefficient between hydrogel and FBG.