| With the progress of society and the development of science and technology,sensors play a more important role in collecting information to replace the manual way.With its advantages,fiber-optic sensors have been widely used in temperature and strain sensing,and have received extensive attention in academic and industrial research in recent decades.The fiber is small in size,light in weight and corrosion-resistant.The fiber-optic sensor is resistant to electromagnetic interference,has a long signal transmission distance,and can realize distributed measurement.Therefore,fiber-optic sensors are widely applied in many applications such as building structure monitoring,seismic monitoring,pipeline cable monitoring,aerospace performance monitoring,security applications and so on.Among the several types of fiber-optic sensor,Brillouin Optical Correlation Domain Analysis(BOCDA)has been widely studied for its superior spatial resolution,extremely high measurement accuracy and ability in dynamic measuring.Compared with other fiber-optic sensors,measurement range of BOCDA is short,which limits its application.Therefore,we aim to achieve a larger sensing range while maintaining its advantages in spatial resolution and measurement accuracy.It is of great significance for BOCDA to gain more applications in the industry.This paper proposes a range-enlarged high-speed BOCDA system,which greatly enlarges the measurement range of the system and achieves a high measurement speed simultaneously.It is of great significance for expanding the application of BOCDA system when sensing in a longer range.By combining the time domain data processing scheme,multiple correlation peaks are simultaneously interrogated,and the measurement range is improved by 80 times in experiment.The injection locking technique is used to eliminate the parasitic intensity modulation of the light source,to improve the sideband suppression ratio,to improve the measurement accuracy and to achieve a high measurement speed of the system.Besides,we add a polarization switch to compensate for signal degradation caused by changes of polarization state in a single-mode fiber,and to eliminate the resulting measurement errors eventually.Through theoretical analysis and experimental verification of the system,a measurement range of 800 m,a spatial resolution of 9 cm,and a measurement accuracy of 2 MHz are realized with a measurement time as short as 250 ms,and the average measurement speed is about 36,000points/s.Compared to the other BOCDA system,the performance of this scheme has been greatly improved.In addition,this paper also introduces the application of BOCDA prototype in temperature monitoring of steel crystallizer.According to the industrial requirement,we conducted an integrated research on the BOCDA system and developed a prototype to monitor the temperature distribution of the crystallizer and verify the application of the BOCDA system in high temperature sensing.After verification by our experiments,the prototype can achieve temperature sensing range within 400 ?,with1.2 cm spatial resolution,0.8 MHz sensing accuracy,and measurement speed of about 5,000 points/s.Finally in the appendix,in order to solve the problem that the Brillouin scattering based sensing system is sensitive to both temperature and strain,a temperature strain separation scheme based on guided acoustic waveguide Brillouin scattering(GAWBS)and stimulated Brillouin scattering(SBS)is proposed.The experimental system realizes the measurement of the SBS signal and the GAWBS signal respectively by switching the pump light signal on and off.From the experiment,the temperature accuracy can be solved to be about 0.7 ? and the strain accuracy is about 13 ??.In summary,this paper proposes a range-enlarged high-speed BOCDA scheme,and then develops a prototype system with conducting temperature monitoring experiments,and proposes a temperature-strain separation scheme,aiming to take advantages of the BOCDA system and expand its application in more fields. |
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