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[IEEE 2018 IEEE 7th International Conference on Photonics (ICP) - Kuah (2018.4.9-2018.4.11)] 2018 IEEE 7th International Conference on Photonics (ICP) - Differential Cross Spectrum Technique for Improving the Spatial Resolution of BOTDR Sensor
摘要： We propose a technique in BOTDR fiber sensor to generate a pair of pulsed probes via intensity modulation scheme for measuring distributed strain at high spatial resolution. The first probe consists of a long- and short duration of pulses separated by a short interval. The second probe only has the long pulse of the first probe. Introducing FFT in correlating the backscattered signals sampled by wide and narrow window functions for each probe gives narrow Brillouin spectrum width. The subtraction of the correlated signals obtained by the two probes results in high spatial resolution measurement. The intensity modulation makes it easier to generate the pair of pulsed probes having the same waveform of the long pulse and to obtain the results according to the measurement principle. We have achieved 0.2 m spatial resolution and 3.2 MHz Brillouin frequency accuracy in measuring a 350 m fiber.
关键词： BOTDR,spatial resolution,distributed fiber sensor,Brillouin frequency shift
更新于2025-09-23 15:23:52
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Drying-induced soil shrinkage and desiccation cracking monitoring with distributed optical fiber sensing technique
摘要： Monitoring of drying-induced volume shrinkage and desiccation cracking in clayey soils is of great importance in geological and geotechnical engineering. Compared with conventional strain monitoring methods providing discrete measurements, the Brilliouin optical time domain reflectometer (BOTDR) technique enables continuous measurement of the distributed strain generated along optical fibers. In this study, a physical model test is conducted to investigate the feasibility of monitoring drying-induced soil shrinkage and desiccation cracking using BOTDR. Three optical fibers with different surface protections (thermoplastic polyester elastomer (TPEE) jacket, nylon jacket, and acrylate coating) are tested and compared. Experimental results validate that BOTDR is applicable for the direct strain monitoring of desiccation cracking soils. Monitored strain values are strongly influenced by water content, soil cracking, and fiber types. The strain measured by the optical fiber reaches only several micro strains when the soil is over-saturated, gradually increases with the decreasing water content and the increasing soil-fiber interfacial shear stresses, and drops rapidly after the occurrence of decoupling between fiber and soil resulting from the mature development of desiccation cracks. The optical fiber with acrylate coating is not suitable because of its fragility and the poor interfacial coupling with the soil. Optical fibers covered with TPEE jacket or nylon jacket are both applicable for soil strain monitoring, with the former one more sensitive to water content variations. The study is the first attempt to apply the BOTDR technique for the direct and continuous monitoring of drying-induced soil shrinkage and desiccation cracking process. It is expected bring new insights into the fundamental understanding of volumetric shrinkage and desiccation cracking in clayey soils.
关键词： Brilliouin optical time domain reflectometer (BOTDR),Desiccation crack,Volumetric shrinkage,Strain monitoring,Optical fiber sensing
更新于2025-09-23 15:21:01
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Monitoring of CFA pile test using three dimensional laser scanning and distributed fiber optic sensors
摘要： The results obtained during a pile test are dependent on a number of factors. However, conventional monitoring systems like vibrating wire strain gauges and the extensometers can only measure the variations of strain and displacement at discrete locations at which they are installed in a pile. In order to identify the behavior of Continuous Flight Auger (CFA) pile, the distributed fiber optic monitoring system and three-dimensional laser scanning collected the strain and point clouds data during the pile test with conventional vibrating wire strain gauges, extensometers. Based on the Brillouin Optical Time Domain Reflectometry (BOTDR) fiber optic strain profile, the profiles of axial load, skin friction, displacement can be obtained. The fiber optic monitoring system was compared with conventional systems, and it was found that the ability to measure the full strain profiles is highly advantageous in determining the performance of the pile and in detecting the behavior of CFA pile. The displacement of the pile was measured by the LVDT at the top of the pile and the results were compared with the laser scanning results. In this study, the negative skin friction was detected by BOTDR fiber optic strain profile near the top of the CFA pile. It was not able to define the reason of the negative skin friction from the other monitoring systems but the laser scanning results show that the ground movement due to the pull-out force of the anchor pile affects the negative skin friction. Although laser scanning is not able to measure the real-time data during the pile test, the extensive information can be taken into account by the monitored data from three-dimensional laser scanning.
关键词： Distributed fiber optic monitoring,BOTDR,CFA pile,Three-dimensional laser scanning
更新于2025-09-19 17:13:59
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[IEEE 2019 2nd International Colloquium on Smart Grid Metrology (SMAGRIMET) - Split, Croatia (2019.4.9-2019.4.12)] 2019 2nd International Colloquium on Smart Grid Metrology (SMAGRIMET) - Fiber Optic Sensor Cable Based on Hollow Capillary Tube with Three Tightly Encapsulated Optical Fibers
摘要： Fiber optic sensor cable technology is relatively new field that combines a set of scientific and technical disciplines in a special way in order to meet industrial standards. In this paper we discuss one particular design for multipurpose and configuration multivalent optical fiber sensing. It has the potential to integrate more detection and measurement techniques in one cable body and this, in turn, largely contributes to installation cost optimization and directly impacts investment plans and industrial success. The article presents also a unique high-pressure high temperature lab facility conceptualized and constructed for testing and evaluation of this and similar optical fiber sensor cables.
关键词： fiber optic measurements,OFDR,acoustic sensors,BOTDA,BOTDR,DAS,Brillouin effect,optical fiber,pressure sensors,fully distributed optical fiber sensor,monitoring systems,strain sensors,temperature sensors,OTDR
更新于2025-09-16 10:30:52