Dr. Wai Lun Sham Profile

Dr. Wai Lun Sham

PhD. candidate at Nanyang Technological Univ

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Proceedings Article | 18 April 2011 Paper

Stability and reliability of fiber optic measurement systems: basic conditions for successful long term structural health monitoring

Pravin Sudhakar Muley, Yaowen Yang, Wai Lun Sham

Proceedings Volume 7983, 798319 (2011) https://doi.org/10.1117/12.881147

KEYWORDS: Sensors, Fiber optics sensors, Structured optical fibers, Coating, Structural health monitoring, Optical fibers, Fiber Bragg gratings, Fiber coatings, Reliability, Fiber optics

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Recent developments in fiber optic sensors for monitoring civil structures have been of great help for engineers dealing with these structures. After literature survey it is observed that while using fiber optic sensor system for health monitoring of civil structures not much attention is given to the core quality of the fiber, types of coating on fiber, implementing methodologies, handling of fiber optic sensors and their long term effect on reliability of the performance of the monitoring system. These issues are important because the structural conditions, stress level and environment in which fiber optic sensors are placed are different from telecommunication industry. In this paper issues related to long term structural health monitoring of civil structures are investigated. The issue of the fatigue property of optic fiber is discussed since reversal bending of the fiber may cause adverse effect on the light carrying capacity of the fiber. Other long term structural health monitoring (SHM) issues such as life of fiber, strain transfer process from fiber core to coating, calibration of fiber and selection of fiber are also discussed based on the experiments carried out for successful implementation of long term health monitoring of civil structures. The main objective of these experiments is to come up with comprehensive long term structural health monitoring system for strain measurement.

Proceedings Article | 1 April 2011 Paper

Customization and calibration of BOTDR sensors for underground structural health monitoring

Wai Lun Sham, Yaowen Yang, Muley Pravin

Proceedings Volume 7984, 79842A (2011) https://doi.org/10.1117/12.880345

KEYWORDS: Sensors, Structural health monitoring, Fiber optics sensors, Coating, Bridges, Temperature metrology, Calibration, Scattering, Sensor calibration, Reflectometry

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In recent years, it is becoming more common to use fiber optic sensors (FOS) in the structural health monitoring (SHM) sector, especially in the civil engineering field. A number of surface-mountable sensor system for FOS have been developed in the past years, the recent development of Brillouin Optical Time Domain Reflectometry (BOTDR) was a great evolution towards the SHM system development, it inspired the new edge of FOS SHM system. Different from the traditional monitoring instruments, it provides distributed, long distance, real-time, interference free and high accuracy/precision measurement data. It is now possible to achieve "continuous" measurement data and this SHM technique is applicable in area that is inaccessible. The research aims to solve the problems which exist in the convergence measurement using the conventional measuring methods, however, there is still a gap between the lab experiments and field applications. Limited research has been conducted on how to maximize its possible applications due to its brittle and fragile material nature. A number of additional considerations for a successful pairing of these two must be taken into account for successful field applications. This article provides a short review on underground monitoring techniques and FOS SHM systems. The focuses is on examine (i) the feasibility and effectiveness of different BOTDR sensors installation methods (ii) the suitable commercially-available o sensing cable for underground application (iii) the sensing performance of customized sensor protection package BOTDR sensor that manufactured involving layers of fiber reinforced composites. This research serves a bridge in between the technology advancement to the creation of a structure health monitoring system with practical application, numerical simulation and theoretical analysis aspects, and also to provide the insights into the mechanisms of BOTDR.

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