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Articles & Applications for Optical Sensing

Bridges
Civil Structures & Engineering
Concrete Beams
Geotechnical
Sensors

General Overview:

Micron Optics Optical Sensing Guide
Copyright 2005 Micron Optics

Bridges:

Health Monitoring of Rehabilitated Concrete Bridges Using Distributed Optical Fiber Sensing
by Wei Zhang,. Junqi Gao, Bin Shi, Heliang Cui, Hong Zhu

"It is evident that a health monitoring system (HMS) holds a great deal of potential to reduce the inspection and maintenance cost[s] of existing highway bridges by identifying the structural deficiencies at an early stage, as well as verifying the efficacy of repair procedures. As newly developed techniques, distributed optical fiber sensing (DOFS) have gradually played a prominent role in structural health monitoring for the last decade. This article focuses on the employment of two types of DOFS, namely fiber Bragg grating (FBG) and Brillouin optical
time domain reflectometry (BOTDR), into an integrated HMS for rehabilitated RC girder bridges by means of a series of static and dynamic loading tests to a simply supported RC T-beam strengthened by externally post-tensioned aramid fiber reinforced polymer (AFRP)
tendons....(read entire article)

Characterizing Aged Bridge Response by Loading Test
Copyright 2005 POFC. This application note posted with permission of POFC

Long Term Structural Health Monitoring of the Hampden Suspension Bridge
Copyright 2005 MOS. This application note posted with permission of Monitor Optics Systems in Australia.

Remote Health Monitoring of a High Performance Steel Bridge Using Fiber Optic Technology
by J.D. Doornink, B.M. Phares, A. Abu-Hawash, T.J. Wipf, D.J. Hemphill, L.F. Greimann

"In early 2004, the Iowa Department of transportation (DOT) completed construction of Iowa's first High Performance Steel (HPS) bridge ...the Bridge Engineering Center at Iowa State University has developed a continuous Structural Health-Monitoring (SHM) system to monitor and record the performance of the HPS bridge for a two-year period. With this system, the bridge performance can be evaluated at any point in time...(read entire article)

To see a live demo, visit the BEC website. (Note: demo only works in Internet Explorer Browser)

Copyright 2004 BEC; posted with permission of the Bridge Engineering Center of the Iowa State University Research Park. For more information regarding the Bridge Engineering Center, go to their www.ctre.iastate.edu.

Structural Health Monitoring of a Steel Railway Bridge using Optical Fibre Bragg Grating Sensors and Numerical Simulation
By George J. Tsamasphyros, Elias A. Koulalis, George N. Kanderakis, Nikos K. Furnarakis, Vangelis Z. Astreinidis

"The application of structural health monitoring techniques to a late 19th century steel railway bridge located at Nea Peramos near Athens Greece, still under regular usage, has been attempted using optical fiber Bragg grating sensors. As a first step, one fiber Bragg grating sensor was placed in the middle of a secondary beam section, exactly below the rail track on the one edge of the bridge and measurements have been retrieved for trains..."(read entire article)

The Application of FBG Sensors in Monitoring the Binzhou Yellow River Bridge of Shandong Province
Copyright 2006 Harbin Institute of Technology (HIT). This application note posted with permission of HIT

Civil Structures & Engineering:

An Industrial Perspective on the Applications of Optical Sensing Technology in Selected Fields
by Allen Cheng, David Wu, Vincent Chang Chien, Patrick Tsai, and I-Wen Wu

A brief take on the optical sensing technology is provided in this paper with a main focus on the FBG technology. This work discusses the components that are required to assemble a proper FBG optical sensing system, namely the sensors, interrogators, signal transmission lines/cables, custom software, and most importantly, the installation work. A few key examples of work done by POFC and collaborators will be presented and discussed.(Read entire article)

Fiber Bragg Grating Sensing for Structural Health Monitoring of Civil Structures
By J. D. Doornink, T.W. Graver, JP Ou, B. M. Phares and Z. Zhou

Structural Health Monitoring (SHM) is fast becoming a highlight of both research and applications in civil engineering. One key driver is the ever-improving function and cost of fiber-optic sensing (FOS) systems. To date, FOS has been used on hundreds of civil structures around the world. This paper focuses on two initiatives that rely on FOS. Researchers from Iowa State University's Bridge Engineering Center demonstrate a novel approach to SHM data management, analysis and presentation. Preliminary results are shown and links to live data are provided. At the Harbin Institute of Technology, civil engineers are studying local damage on large-span bridges. Current work focuses on solving key practical challenges for several existing and new large spans.
(Read entire article)

Growing Market Acceptance for Fiber-Optic Solutions in Civil Structures
By T.W. Graver, D. Inaudi, J. Doornink

Owners must manage and ensure the safety of their civil structures even as use of many structures extends well beyond their design lifetime. Traditionally, most structures rely on strict maintenance procedures, visual inspections, and very few sensors. But maintenance is very expensive, visual inspections can miss critical problems, and conventional sensors can fail in harsh environments. Can fiber-optic sensing (FOS) address these issues? This is not a new question, but there are some new answers. This paper highlights several structures where FOS is used, and describes the associated successes and challenges for each application. Many successes are coupled to improved FOS tools: better sensor packages, simpler and less expensive instrumentation, improved installation techniques, and more efficient data analysis tools. Examples of each are provided. Particular attention is given to the economics of instrumenting civil structures - when and how it pays. Conclusions include recommendations for future developments that will further accelerate FOS acceptance and use. (Read entire article)

Recent Progress on Structural Health Monitoring by Fibre Optic Sensor In Civil Engineering
By Hong-Nan LI, Liang Ren

view presentation

Concrete Beams:

Smart FRP-OFBG Bars and their Application in Reinforced Concrete Beams
by Z. Zhou, J.P. Ou & B. Wang

"Fiber Reinforced Polymer (FRP) has become more and more popular as construction material in civil engineering due to its advantages of corrosion-resistance, high strength, nonmagnetic, fatigue-resistance... Optical Fiber Bragg Grating (OFBG) is now widely accepted as [a] smart sensor due to its advantages of electric-magnetic resistance, small size, distributing measurement, durability, and so on. Combined the strength properties of FRP with the sensing properties of OFBG, a new kind of smart FRP-OFBG composite bars has been developed.... The
experiment of FRP-OFBG reinforced concrete beams under static load has been done, and ....(read entire article)

Geotechnical:

Applications of Optical Fiber Sensor on Local Scour Monitoring
By Yung Bin Lin, Kuo Chun Chang, Jihn-Sung Lai, I-Wen Wu

"Scour is one of the major causes for bridge failure. A real-time optical fiber sensory system for bridge scour, using fiber Bragg grating (FBG) sensors, has been developed and tested. These optical fiber sensors, especially the FBG scour-monitoring system, can measure both the process of scouring and the variation of water level change. Several test runs have been conducted in the laboratory and in-site bridge to demonstrate the applicability of the FBG system. The results have shown that the system has the potential to be applied in the field to a real-time monitoring application for bridge scouring.."(read entire article)

Establishment [of] the Bridge Scour Safety Monitoring System by Using Fiber Bragg Grating Sensors Introduction
By Yung Bin Lin, Kuo Chun Chang

"... Scouring at a bridge pier in the river can be caused by general scour, contraction scour or local scour. Among them, local scour is the most critical and generally caused by the interference of the structures with river flow. In the present study, it is shown that the FBG sensors have demonstrated the capability to measure the water level, scour depth and deposition height at the Dadu Bridge. The field results indicate that the real-time monitoring system using FBG sensors have the potential for real world applications."(Read entire article)

Long-term Monitoring of Seismic Changes of a Key Fault
Copyright 2005 POFC; posted with permission of Prime Optical Fiber Corporation.

Real Time Subsea Monitoring and Control Smart Field Solutions
by D. Brower and N. Prescott

A new method to monitor and control subsea pipelines and facilities is in development. The new method involves the integration of the latest technology advancements in the industry coupled with standard state-of-the-art pipeline technology. The result is a pipeline and facilities system that is auto adaptive to the environment so that real-time problem identification and corrective action can be implemented. Potential pipeline problems will be mitigated to avoid costly down time and repair. The technology will significantly reduce environmental contamination concerns. It is expected that years of trouble free pipeline usage will be possible with an enhanced overall service life expectancy.(Read entire article)

Real-time Flow Assurance Monitoring with Non-intrusive Fiber Optics Technology
by D. Brower, N. Prescott, J. Zhang, C. Howerter, D. Rafferty

Flow assurance is a key aspect of offshore, particularly deepwater developments. Tremendous progress during the past two decades in the understanding of the issues and the required technology has enabled the developments be designed and operated with low risk of flow assurance problems. However, the problems have not been eliminated due to system component failures or un-designed for operating conditions. Real time monitoring of the production and transportation system can help significantly reduce the occurrence and impact. The present paper discusses the use of non-intrusive fiber optic technology for this purpose. (read entire article)

Sensors:

Fiber Sensors Lay Groundwork for Structural Heath Monitoring
Copyright 2006 Laser Focus World, February 2006 issue

Combined Static and Dynamic Monitoring of Civil Structures with Long-gauge Fiber Optic Sensors
By D. Inaudi, J.W. Miller, and T.W. Graver

Abstract: Long-gauge SOFO® sensors have been in use for the last 10 years for the monitoring of civil, geotechnical, oil & gas and other structures. More than 3500 sensors have been installed worldwide in a number of different structure types. The original demodulation system is based on low-coherence interferometry and is particularly suitable for the monitoring of long-term static deformations. This paper reports the development and testing of a new sensing system based on Fiber Bragg Gratings and allowing the monitoring of both the static as the dynamic response of structures. The sensors are based on the well-proven SOFO packaging and allow the measurement of deformations over measurement basis of 2m, with a resolution of 1 microstrain and a frequency of 250 Hz. The system is insensitive to temperature variations, electromagnetic disturbances (electric power lines, lightning) and has demonstrated excellent long-term stability and durability. Each sensor also contains a temperature gauge, useful for the evaluation of the ambient parameters. (read entire article)

Experimental Investigation of Optical Waveguide-Based Multigas Sensing
By Wei Peng, Gary Pickrell, Fabin Shen, and Anbo Wang

Abstract: In this letter, the results of an experimental investigation for simultaneous multiple gas detection utilizing an optical fiber sensor are described. The optical fiber system used for these experiments contained a section of hollow tubing and this allowed a combination of gas molecular absorption with optical waveguide technology. A fiber-optic sensing structure was designed and demonstrated which can monitor multiple gases simultaneously. The experimental results demonstrate the characteristic absorptions in the optical spectra corresponding to the narrow molecular absorption lines of the gases tested, which included acetylene and carbon monoxide.

For the full paper, visit http://ieeexploer.ieee.org

In-Situ Failure Identification in Woven Composites throughout Impact using Fiber Bragg Grating Sensors
By James Pearson, Mohanraj Prabhugoud, Mohammed Zikry, Kara Peters

Abstract: In this study, measurements from low-impact velocity experiments and surface mounted optical fiber Bragg grating (FBG) sensors were used to obtain detailed information pertaining to damage progression in two-dimensional laminate woven composites. The woven composites were subjected to multiple strikes at 2m/s until perforation occurred, and the impactor position and acceleration were monitored throughout each event. From these measurements, we obtained dissipated energies and contact forces. The FBG sensors were surface mounted at different critical locations near penetration-induced damaged regions. These FBG sensors were used to obtain initial residual strains and axial and transverse strains that correspond to matrix cracking and delamination (read entire paper).

Miniature Fiber-Optic Pressure Sensor
By Yizheng Zhu, and Anbo Wang

Abstract: This letter presents a miniature fiber-optic pressure sensor fabricated directly on the tip of a fiber. The sensor measures only 125 /spl mu/m in diameter. A Fabry-Pe/spl acute/rot cavity and a thin silica diaphragm are fabricated by simple techniques involving only fusion splicing, cleaving, and wet chemical etching. Interference pattern of the sensor is analyzed and issues in sensor design are discussed. The sensor has been tested for static pressure response, showing excellent repeatability and no hysteresis. Its all-fused-silica structure lends it great potential for high-temperature pressure measurements. Pressure testing results at 530/spl deg/C are given. The sensor may also find uses in medical applications.

For the full paper, visit http://ieeexploer.ieee.org

Process for Mounting and Packaging of Fiber Bragg Grating Strain Sensors for use in Harsh Environment Applications
By V.P. Wnuk, A. Mendez, S. Ferguson, and T.W. Graver

Abstract: Over the last few years, optical fiber sensors have seen an increased acceptance as well as a widespread use for structural sensing and monitoring in civil engineering, aerospace, marine, oil & gas, composites and smart structure applications... However, one of the areas in need of further development and commercial maturity is that of sensor packaging and installation technique...

In this paper, we report the development of a new bonding agent and method for the surface mounting of optical fiber Bragg grating strain and temperature sensors for use in harsh environments--where there is a presence of water, moisture, dust, susceptibility to corrosion and/or elevated temperatures up to 500 °C. The compound is based on a combination of ceramic fillers with an epoxy binder that is applied with a brush technique. The mounting procedure will be discussed along with experimental results on the sensor's strain and temperature response under controlled environmental conditions. (Read entire article)

Note: this paper was delivered at the 2005 Smart Structures/NDE conference in San Diego, California, March 8-9, 2005.

Radiation and Cladding Modes as Independent Measurements of Bragg Grating Sensor Integrity
By Mohanraj Prabhugoud, James Pearson, Kara Peters, and Mohammed Zikry

Abstract: This article presents the use of Bragg reflection and cladding mode measurements to independently measure axial strain and the integrity of a Bragg grating sensor. While the Bragg reflection is known to be sensitive to applied strain, the cladding modes are shown to be sensitive to expected damage within the sensor such as microcracking and debonding from the host structure. This phenomenon allows the intelligent self-testing of the Bragg grating sensor without additional instrumentation and permits the separate identification of sensor failure from the failure of the host structure. The growth of cladding modes during degradation of a Bragg grating is experimentally demonstrated in controlled tension tests with different fiber-host interface conditions.

Note: this paper was delivered at the 2005 Smart Structures/NDE conference in San Diego, California, March 8-9, 2005.

Review of Fiber Optic Accelerometers
By C. Baldwin, J. Niemczuk, J. Kiddy, and T.Salter

Abstract: Over the past decade, the proliferation of fiber optic sensors and sensing systems has been ever increasing, especially the use of fiber Bragg grating (FBG) based sensors. These sensors have been mainly relegated to research applications with a few noted large-scale structural tests. The main sensing parameters for these tests have been strain and/or temperature. This paper discusses the development of accelerometers with FBG sensors as the measurement medium. The discussion includes a brief overview of FBG sensors, the functionality of FBG sensors as accelerometers, aspects of commercially available instrumentation for monitoring the accelerometers, and experimental data from three commercially available accelerometer designs. The purpose of this paper is to provide the modal analysis community with an understanding of the current state-of-the-art in fiber Bragg grating sensors for dynamic and vibration testing. (read entire article)

Copyright 2005 SPA. This paper was delivered at the IMAC XXIII Conference & Exposition on Structural Dynamics, January 31 - February 3, 2005. Used with permission of Systems Planning and Analysis, Inc. For more information on SPA, go to their website www.spa.com/aedp.htm

Techniques of Advanced FBG sensors: fabrication, demodulation, encapsulation
and their application in the structural health monitoring of bridges
By Z. Zhou, T. W. Graver, L. Hsu, JP Ou

FBG(Fiber Bragg Grating) sensors have been more and more accepted by engineers in structural health monitoring(SHM). This paper has given a brief introduction on the practical techniques of fabrication and demodulation on FBG sensors. Aiming at the practical applications in infrastructures, the techniques of FBG encapsulation techniques are developed. And their applications in the structural health monitoring of bridges are conducted. Finally, some problems of FBG sensors when used in practical infrastructures are put forward and the solutions are also suggested. (Read entire article)

Optical Fiber Sensors as Mechanical Strain Gauges: A Review
By A. Mendez, S. Ferguson, and T.W. Graver

...One of the most common applications [of optical fiber sensors] is that of strain/stress sensing. A variety of discrete fiber strain sensors based on Fabry-Perot cavities and fiber Bragg gratings, as well as distributed techniques based on Brillouin scattering methods have been developed along with pertinent interrogation electronics and instruments. However, to many technical communities outside the field of optical fiber technology, the actual operating principles of these devices and their potential utilization is not well understood. This lack of familiarity and understanding is preventing the adoption and diversification of the technology in fields where it can offer significant functional and commercial benefits over conventional sensing means-- as is the case in the general area of experimental mechanics.

In this paper, we present an overview on the state-of-the-art of optical fiber strain sensing technology and describe the operating principles and design of different sensors and interrogation techniques. An analysis of the fundamental strain response for fiber Bragg grating and Fabry-Perot strain sensors will be presented, and compared to that of a conventional foil strain gauge. Factors affecting the strain sensitivity and response of fiber devices such as bonding, sensor placement, strain field and sensor host interplay will be described. Static and dynamic strain responses and use in harsh environments will also be described.

Note: this paper was delivered at the 2005 SEM Annual Conference & Exposition on Experimental and Applied Mechanics in Portland,Oregon, June 7-9, 2005.