Network Integration of Distributed Optical Fiber Temperature Sensor

The integration of distributed optical fiber temperature sensor with supervisory control and data acquisition （SCADA） system is proposed and implemented. In the implementation of the integration, both the compatibility with traditional system and the characteristics of distributed optical fiber temperature sensor is considered before Modbus TCP/IP protocol is chosen. The protocol is implemented with open source component Indy. The Modbus TCP/IP protocol used in the system is proved to be fast and robust.

Landslide Monitoring Based on High-Resolution Distributed Fiber Optic Stress Sensor

A landslide monitoring application is presented by using a high-resolution distributed fiber optic stress sensor. The sensor is used to monitor the intra-stress distribution and variations in landslide bodies, and can be used for the early warning of the occurrence of the landslides. The principle of distributed fiber optic stress sensing and the intra-stress monitoring method for landslides are described in detail. By measuring the distributed polarization mode coupling in the polarization-maintaining fiber, the distributed fiber stress sensor with stress measuring range 0 to 15 MPa, spatial resolution 10 cm and measuring range 0.5 km, is designed. The warning system is also investigated experimentally in the field trial.

Distributed fiber optic monitoring of a CFA pile with a central reinforcement bar bundle

In this paper,we present an application of distributed fiber optic sensor(DFOS)technology to measure the strain of a continuous flight auger(CFA)test pile with a central reinforcement bar bundle,during a static load test carried out in London.Being distributed in nature,DFOS gives much more information about the pile performance as compared to traditional point sensors,such as identifying cross-sectional irregularities or other anomalies.The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation(contraction),shaft friction,and tip resistance under various loads.Based on this pile load test,a finite element(FE)analysis was performed using a one-dimensional nonlinear load-transfer model.Calibrated by the shaft friction and tip resistance derived from the monitored data,the FE model was able to simulate the pile and soil performance during the load testing with good accuracy.The effect of the reinforcement cage and central reinforcement bar bundle were investigated,and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%.

Development of Fully-Distributed Fiber Sensors Based on Brillouin Scattering

Brillouin scattering based optical fiber sensors(BOFS)have the unique advantages over other sensors such as long distance,fully distributed,and multi-parameter sensing.The progresses on the development of BOFS technology in Nanjing University are reviewed.The key technologies to make BOFS with ultra-long distance,high spatial resolution,and fast measuring speed are discussed and realized.

High sensitivity cascaded helical-core fiber SPR sensors

The distributed optical fiber surface plasmon resonance(SPR)sensors have attracted wide attention in biosensing and chemical sensing applications.However,due to the limitation of their sensing structure,it is difficult to adjust their res-onant wavelength and sensitivity.Here,novel and flexible cascaded helical-core fiber[HCF)SPR sensors are proposed theoretically and experimentally for distributed sensing applications.It is shown that the resonant wavelength and sensitivity of the sensors can be conveniently controlled by adjusting the twist pitch of the helical core.A high sensitivity of 11,180 nm/RIU for refractive-index measurement ranging from 1.355 to 1.365 is realized experimentally when the twist pitch of the helical core is 1.5 mm.It is worth noting that the sensitivity can be further improved by reducing the twist pitch.For example,the sensitivity of the sensor with a twist pitch of 1.4 mm can theoretically exceed 20,000 nm/RIU.This work opens up a new way to implement multi-parameter or distributed measurement,especially to establish sensing networks integrated in a single-core fiber or a multi-core fiber.

A novel smart steel strand based on optical-electrical co-sensing for full-process and full-scale monitoring of prestressing concrete structures

As the main load bearing component,the steel strand has a significant impact on the safety of civil infrastructure.Real-time monitoring of steel strand stress distribution throughout the damage process is an impor-tant aspect of civil infrastructure health assessment.Hence,this study proposes an optical-electrical co-sensing(OECS)smart steel strand with the DOFS and CCFPI embedded in.It can simultaneously measure small strains in the initial damage phase with high accuracy and obtain information in the large deformation phase with relatively low precision.Several experiments were carried out to test its sensing performance.It shows both DOFS and CCFPI have good linearity,repeatability and hysteresis.In comparison to DOFS,CCFPI has a relatively lower accuracy and resolution,but a large enough measurement range to tolerate the large strain in the event of a steel strand failure.To verify the reliability of the proposed smart steel strand in real structures,the strand strain distribution in the full damage process of bonded prestressed beams under four-point bending loading was monitored using the smart steel strand as a prestressing tendon.The strain measured by the OECS steel strand is shown to reflect the deformation and stiffness variation of prestressed beams under different load.

DFOS Applications to Geo-Engineering Monitoring

Optical fiber sensing technology has developed rapidly since the 1980s with the development of the optical fiber and fiber optical communication technology.It is a new type of sensing technology that uses light as a carrier and optical fiber as a medium to sense and transmit external signals(measurands).Distributed fiber optical sensors(DFOS)can continuously measure the external physical parameters distributed along the geometric path of the optical fiber.Meanwhile,the spatial distribution and change information of the measured physical parameters over time can be obtained.This technology has unmatched advantages over traditional point-wise and electrical measurement monitoring technologies.This paper summarizes the state-of-the-art research of the application of the distributed optical fiber sensing tech no logy in geo-engineering in the past 10 years,mainly including the advantages of DFOS,the challenges in geo-engineering monitoring,related fundamental theoretical issues,sensing performance of the optical sensing cables,distributed optical fiber monitoring system for geo-engineering,and applications of optical fiber sensing technology in geo-engineering.