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3123 KiB

Open AccessArticle

A Micro-Computed Tomography Technique to Study the Quality of Fibre Optics Embedded in Composite Materials

by Gabriele Chiesura, Geert Luyckx, Eli Voet, Nicolas Lammens, Wim Van Paepegem, Joris Degrieck, Manuel Dierick, Luc Van Hoorebeke, Pieter Vanderniepen, Sanne Sulejmani, Camille Sonnenfeld, Thomas Geernaert and Francis Berghmans

Sensors 2015, 15(5), 10852-10871; https://doi.org/10.3390/s150510852 - 7 May 2015

Cited by 14 | Viewed by 7103

Abstract

Quality of embedment of optical fibre sensors in carbon fibre-reinforced polymers plays an important role in the resultant properties of the composite, as well as for the correct monitoring of the structure. Therefore, availability of a tool able to check the optical fibre [...] Read more.

Quality of embedment of optical fibre sensors in carbon fibre-reinforced polymers plays an important role in the resultant properties of the composite, as well as for the correct monitoring of the structure. Therefore, availability of a tool able to check the optical fibre sensor-composite interaction becomes essential. High-resolution 3D X-ray Micro-Computed Tomography, or Micro-CT, is a relatively new non-destructive inspection technique which enables investigations of the internal structure of a sample without actually compromising its integrity. In this work the feasibility of inspecting the position, the orientation and, more generally, the quality of the embedment of an optical fibre sensor in a carbon fibre reinforced laminate at unit cell level have been proven. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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679 KiB

Open AccessArticle

Novel Fiber Optic Sensor Probe with a Pair of Highly Reflected Connectors and a Vessel of Water Absorption Material for Water Leak Detection

by Tae-Sik Cho, Ki-Sun Choi, Dae-Cheol Seo, Il-Bum Kwon and Jung-Ryul Lee

Sensors 2012, 12(8), 10906-10919; https://doi.org/10.3390/s120810906 - 7 Aug 2012

Cited by 17 | Viewed by 8351

Abstract

The use of a fiber optic quasi-distributed sensing technique for detecting the location and severity of water leakage is suggested. A novel fiber optic sensor probe is devised with a vessel of water absorption material called as water combination soil (WCS) located between [...] Read more.

The use of a fiber optic quasi-distributed sensing technique for detecting the location and severity of water leakage is suggested. A novel fiber optic sensor probe is devised with a vessel of water absorption material called as water combination soil (WCS) located between two highly reflected connectors: one is a reference connector and the other is a sensing connector. In this study, the sensing output is calculated from the reflected light signals of the two connectors. The first reflected light signal is a reference and the second is a sensing signal which is attenuated by the optical fiber bending loss due to the WCS expansion absorbing water. Also, the bending loss of each sensor probe is determined by referring to the total number of sensor probes and the total power budget of an entire system. We have investigated several probe characteristics to show the design feasibility of the novel fiber sensor probe. The effects of vessel sizes of the probes on the water detection sensitivity are studied. The largest vessel probe provides the highest sensitivity of 0.267 dB/mL, while the smallest shows relatively low sensitivity of 0.067 dB/mL, and unstable response. The sensor probe with a high output value provides a high sensitivity with various detection levels while the number of total installable sensor probes decreases. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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433 KiB

Open AccessArticle

A Sensing Element Based on a Bent and Elongated Grooved Polymer Optical Fiber

by Wei-Hua Lu, Li-Wen Chen, Wen-Fu Xie and Yung-Chuan Chen

Sensors 2012, 12(6), 7485-7495; https://doi.org/10.3390/s120607485 - 1 Jun 2012

Cited by 17 | Viewed by 6341

Abstract

An experimental and numerical investigation is performed into the power loss induced in grooved polymer optical fibers (POFs) subjected to combined bending and elongation deformations. The power loss is examined as a function of both the groove depth and the bend radius. An [...] Read more.

An experimental and numerical investigation is performed into the power loss induced in grooved polymer optical fibers (POFs) subjected to combined bending and elongation deformations. The power loss is examined as a function of both the groove depth and the bend radius. An elastic-plastic three-dimensional finite element model is constructed to simulate the deformation in the grooved region of the deformed specimens. The results indicate that the power loss increases significantly with an increasing bending displacement or groove depth. Specifically, the power loss increases to as much as 12% given a groove depth of 1.1 mm and a bending displacement of 10 mm. Based on the experimental results, an empirical expression is formulated to relate the power loss with the bending displacement for a given groove depth. It is shown that the difference between the estimated power loss and the actual power loss is less than 2%. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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835 KiB

Open AccessArticle

A Wide Dynamics and Fast Scan Interrogating Method for a Fiber Bragg Grating Sensor Network Implemented Using Code Division Multiple Access

by Youngbok Kim, Sie-Wook Jeon, Won-Bae Kwon and Chang-Soo Park

Sensors 2012, 12(5), 5888-5895; https://doi.org/10.3390/s120505888 - 8 May 2012

Cited by 11 | Viewed by 6854

Abstract

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two [...] Read more.

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 μe and a low crosstalk of 950:1. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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303 KiB

Open AccessArticle

Double-Ended Calibration of Fiber-Optic Raman Spectra Distributed Temperature Sensing Data

by Nick Van de Giesen, Susan C. Steele-Dunne, Jop Jansen, Olivier Hoes, Mark B. Hausner, Scott Tyler and John Selker

Sensors 2012, 12(5), 5471-5485; https://doi.org/10.3390/s120505471 - 27 Apr 2012

Cited by 186 | Viewed by 12611

Abstract

Over the past five years, Distributed Temperature Sensing (DTS) along fiber optic cables using Raman backscattering has become an important tool in the environmental sciences. Many environmental applications of DTS demand very accurate temperature measurements, with typical RMSE [...] Read more.

Over the past five years, Distributed Temperature Sensing (DTS) along fiber optic cables using Raman backscattering has become an important tool in the environmental sciences. Many environmental applications of DTS demand very accurate temperature measurements, with typical RMSE < 0.1 K. The aim of this paper is to describe and clarify the advantages and disadvantages of double-ended calibration to achieve such accuracy under field conditions. By measuring backscatter from both ends of the fiber optic cable, one can redress the effects of differential attenuation, as caused by bends, splices, and connectors. The methodological principles behind the double-ended calibration are presented, together with a set of practical considerations for field deployment. The results from a field experiment are presented, which show that with double-ended calibration good accuracies can be attained in the field. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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1231 KiB

Open AccessArticle

Full-Scale Prestress Loss Monitoring of Damaged RC Structures Using Distributed Optical Fiber Sensing Technology

by Chunguang Lan, Zhi Zhou and Jinping Ou

Sensors 2012, 12(5), 5380-5394; https://doi.org/10.3390/s120505380 - 27 Apr 2012

Cited by 32 | Viewed by 10516

Abstract

For the safety of prestressed structures, prestress loss is a critical issue that will increase with structural damage, so it is necessary to investigate prestress loss of prestressed structures under different damage scenarios. Unfortunately, to date, no qualified techniques are available due to [...] Read more.

For the safety of prestressed structures, prestress loss is a critical issue that will increase with structural damage, so it is necessary to investigate prestress loss of prestressed structures under different damage scenarios. Unfortunately, to date, no qualified techniques are available due to difficulty for sensors to survive in harsh construction environments of long service life and large span. In this paper, a novel smart steel strand based on the Brillouin optical time domain analysis (BOTDA) sensing technique was designed and manufactured, and then series of tests were used to characterize properties of the smart steel strands. Based on prestress loss principle analysis of damaged structures, laboratory tests of two similar beams with different damages were used to verify the concept of full-scale prestress loss monitoring of damaged reinforced concrete (RC) beams by using the smart steel strands. The prestress losses obtained from the Brillouin sensors are compared with that from conventional sensors, which provided the evolution law of prestress losses of damaged RC beams. The monitoring results from the proposed smart strand can reveal both spatial distribution and time history of prestress losses of damaged RC beams. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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1497 KiB

Open AccessArticle

Fiber Optic Sensor for Acoustic Detection of Partial Discharges in Oil-Paper Insulated Electrical Systems

by Julio Posada-Roman, Jose A. Garcia-Souto and Jesus Rubio-Serrano

Sensors 2012, 12(4), 4793-4802; https://doi.org/10.3390/s120404793 - 12 Apr 2012

Cited by 95 | Viewed by 12463

Abstract

A fiber optic interferometric sensor with an intrinsic transducer along a length of the fiber is presented for ultrasound measurements of the acoustic emission from partial discharges inside oil-filled power apparatus. The sensor is designed for high sensitivity measurements in a harsh electromagnetic [...] Read more.

A fiber optic interferometric sensor with an intrinsic transducer along a length of the fiber is presented for ultrasound measurements of the acoustic emission from partial discharges inside oil-filled power apparatus. The sensor is designed for high sensitivity measurements in a harsh electromagnetic field environment, with wide temperature changes and immersion in oil. It allows enough sensitivity for the application, for which the acoustic pressure is in the range of units of Pa at a frequency of 150 kHz. In addition, the accessibility to the sensing region is guaranteed by immune fiber-optic cables and the optical phase sensor output. The sensor design is a compact and rugged coil of fiber. In addition to a complete calibration, the in-situ results show that two types of partial discharges are measured through their acoustic emissions with the sensor immersed in oil. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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Graphical abstract

1358 KiB

Open AccessArticle

Parametric Study of the Reflective Periodic Grating for In-Plane Displacement Measurement Using Optical Fibers

by Yeon-Gwan Lee, Dae-Hyun Kim and Chun-Gon Kim

Sensors 2012, 12(4), 4265-4280; https://doi.org/10.3390/s120404265 - 28 Mar 2012

Cited by 2 | Viewed by 7028

Abstract

This paper presents a technique for a simple sensing principle that can be used for the measurement of displacement. The proposed sensor head is composed of a reflective grating panel and an optical fiber as a transceiver. The simplified layout contributes to resolving [...] Read more.

This paper presents a technique for a simple sensing principle that can be used for the measurement of displacement. The proposed sensor head is composed of a reflective grating panel and an optical fiber as a transceiver. The simplified layout contributes to resolving the issues of space restraints during installation and complex cabling problems in transmission fiber optic sensors. In order to verify the effectiveness of the proposed technique, it is important to obtain the sinusoidal signal reflected from the grating for reasonable phase tracking. In the numerical analysis, a real wave based optical beam model is proposed for the extraction of predicted signal according to the grating width and ratio of reflection bar width to spacing. The grating pattern design to obtain a sine wave reflected sensor signal was determined within an R-square value of 0.98 after sine curve fitting analysis. Consequently, the proposed sensor principle achieved the in-plane displacement measurement with a maximum accuracy error of 5.34 µm. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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596 KiB

Open AccessArticle

Sensitivity Enhancement of Strain Sensing Utilizing a Differential Pair of Fiber Bragg Gratings

by Zhiyong Zhang, Lianshan Yan, Wei Pan, Bin Luo, Ping Wang, Likang Guo and Wei Zhou

Sensors 2012, 12(4), 3891-3900; https://doi.org/10.3390/s120403891 - 26 Mar 2012

Cited by 19 | Viewed by 6817

Abstract

In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to [...] Read more.

In strain measurement applications, the matched fiber Bragg gratings (FBG) method is generally used to reduce temperature dependence effects. The FBG parameters have to be designed to meet the requirements by the particular application. The bandwidth and slope of the FBG has to be balanced well, according to the measurement range, accuracy and sensitivity. A sensitivity enhanced strain demodulation method without sacrificing the measurement range for FBG sensing systems is proposed and demonstrated utilizing a pair of reference FBGs. One of the reference FBGs and the sensing FBG have almost the same Bragg wavelength, while the other reference FBGs has a Bragg wavelength offset relative to the sensing FBG. Reflected optical signals from the sensing FBG pass through two reference FBGs, and subtract from each other after the detection. Doubled strain measurement sensitivity is obtained by static rail load experiments compared to the general matched grating approach, and further verified in dynamic load experiments. Experimental results indicate that such a method could be used for real-time rail strain monitoring applications. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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361 KiB

Open AccessArticle

A Fiber Optic Catalytic Sensor for Neutral Atom Measurements in Oxygen Plasma

by Rok Zaplotnik, Alenka Vesel and Miran Mozetic

Sensors 2012, 12(4), 3857-3867; https://doi.org/10.3390/s120403857 - 26 Mar 2012

Cited by 23 | Viewed by 6944

Abstract

The presented sensor for neutral oxygen atom measurement in oxygen plasma is a catalytic probe which uses fiber optics and infrared detection system to measure the gray body radiation of the catalyst. The density of neutral atoms can be determined from the temperature [...] Read more.

The presented sensor for neutral oxygen atom measurement in oxygen plasma is a catalytic probe which uses fiber optics and infrared detection system to measure the gray body radiation of the catalyst. The density of neutral atoms can be determined from the temperature curve of the probe, because the catalyst is heated predominantly by the dissipation of energy caused by the heterogeneous surface recombination of neutral atoms. The advantages of this sensor are that it is simple, reliable, easy to use, noninvasive, quantitative and can be used in plasma discharge regions. By using different catalyst materials the sensor can also be applied for detection of neutral atoms in other plasmas. Sensor design, operation, example measurements and new measurement procedure for systematic characterization are presented. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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635 KiB

Open AccessArticle

Durability Tests of a Fiber Optic Corrosion Sensor

by Kai Tai Wan and Christopher K.Y. Leung

Sensors 2012, 12(3), 3656-3668; https://doi.org/10.3390/s120303656 - 16 Mar 2012

Cited by 20 | Viewed by 8349

Abstract

Steel corrosion is a major cause of degradation in reinforced concrete structures, and there is a need to develop cost-effective methods to detect the initiation of corrosion in such structures. This paper presents a low cost, easy to use fiber optic corrosion sensor [...] Read more.

Steel corrosion is a major cause of degradation in reinforced concrete structures, and there is a need to develop cost-effective methods to detect the initiation of corrosion in such structures. This paper presents a low cost, easy to use fiber optic corrosion sensor for practical application. Thin iron film is deposited on the end surface of a cleaved optical fiber by sputtering. When light is sent into the fiber, most of it is reflected by the coating. If the surrounding environment is corrosive, the film is corroded and the intensity of the reflected signal drops significantly. In previous work, the sensing principle was verified by various experiments in laboratory and a packaging method was introduced. In this paper, the method of multiplexing several sensors by optical time domain reflectometer (OTDR) and optical splitter is introduced, together with the interpretation of OTDR results. The practical applicability of the proposed sensors is demonstrated in a three-year field trial with the sensors installed in an aggressive marine environment. The durability of the sensor against chemical degradation and physical degradation is also verified by accelerated life test and freeze-thaw cycling test, respectively. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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324 KiB

Open AccessArticle

Amplified OTDR Systems for Multipoint Corrosion Monitoring

by Jehan F. Nascimento, Marcionilo J. Silva, Isnaldo J. S. Coêlho, Eliel Cipriano and Joaquim F. Martins-Filho

Sensors 2012, 12(3), 3438-3448; https://doi.org/10.3390/s120303438 - 12 Mar 2012

Cited by 13 | Viewed by 6994

Abstract

We present two configurations of an amplified fiber-optic-based corrosion sensor using the optical time domain reflectometry (OTDR) technique as the interrogation method. The sensor system is multipoint, self-referenced, has no moving parts and can measure the corrosion rate several kilometers away from the [...] Read more.

We present two configurations of an amplified fiber-optic-based corrosion sensor using the optical time domain reflectometry (OTDR) technique as the interrogation method. The sensor system is multipoint, self-referenced, has no moving parts and can measure the corrosion rate several kilometers away from the OTDR equipment. The first OTDR monitoring system employs a remotely pumped in-line EDFA and it is used to evaluate the increase in system reach compared to a non-amplified configuration. The other amplified monitoring system uses an EDFA in booster configuration and we perform corrosion measurements and evaluations of system sensitivity to amplifier gain variations. Our experimental results obtained under controlled laboratory conditions show the advantages of the amplified system in terms of longer system reach with better spatial resolution, and also that the corrosion measurements obtained from our system are not sensitive to 3 dB gain variations. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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1015 KiB

Open AccessArticle

Dynamic Strain Measured by Mach-Zehnder Interferometric Optical Fiber Sensors

by Shiuh-Chuan Her and Chih-Min Yang

Sensors 2012, 12(3), 3314-3326; https://doi.org/10.3390/s120303314 - 8 Mar 2012

Cited by 27 | Viewed by 9584

Abstract

Optical fibers possess many advantages such as small size, light weight and immunity to electro-magnetic interference that meet the sensing requirements to a large extent. In this investigation, a Mach-Zehnder interferometric optical fiber sensor is used to measure the dynamic strain of a [...] Read more.

Optical fibers possess many advantages such as small size, light weight and immunity to electro-magnetic interference that meet the sensing requirements to a large extent. In this investigation, a Mach-Zehnder interferometric optical fiber sensor is used to measure the dynamic strain of a vibrating cantilever beam. A 3 × 3 coupler is employed to demodulate the phase shift of the Mach-Zehnder interferometer. The dynamic strain of a cantilever beam subjected to base excitation is determined by the optical fiber sensor. The experimental results are validated with the strain gauge. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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648 KiB

Open AccessArticle

Near Infrared Characterization of Hetero-Core Optical Fiber SPR Sensors Coated with Ta₂O₅ Film and Their Applications

by Keiju Takagi and Kazuhiro Watanabe

Sensors 2012, 12(2), 2208-2218; https://doi.org/10.3390/s120202208 - 15 Feb 2012

Cited by 27 | Viewed by 9114

Abstract

This paper describes the characteristics of optical fiber sensors with surface plasmon resonance (SPR) at 1,310 nm in which the scattering loss of silica optical fiber is low. SPR operation in the infrared wavelength range is achieved by coating a thin tantalum pentaoxide [...] Read more.

This paper describes the characteristics of optical fiber sensors with surface plasmon resonance (SPR) at 1,310 nm in which the scattering loss of silica optical fiber is low. SPR operation in the infrared wavelength range is achieved by coating a thin tantalum pentaoxide (Ta₂O₅) film. The novelty of this paper lies in the verification of how the hetero-core scheme could be operated as a commercial base candidate in the sense of easy fabrication, sufficient mechanical strength, and significant sensitivity as a liquid detector under the basis of a low loss transmission network in the near infrared wavelength region. The effect of Ta₂O₅ layer thickness has been experimentally revealed in the wavelength region extending to 1,800 nm by using the hetero-core structured optical fiber. SPR characterizations have been made in the wavelength region 1,000–1,300 nm, showing the feasible operation at the near infrared wavelength and the possible practical applications. In addition, the technique developed in this work has been interestingly applied to a multi-point water-detection and a water-level gauge in which tandem-connected SPR sensors system using hetero-core structured fibers were incorporated. The detailed performance characteristics are also shown on these applications. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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696 KiB

Open AccessArticle

FBG Sensor for Contact Level Monitoring and Prediction of Perforation in Cardiac Ablation

by Siu Chun Michael Ho, Mehdi Razavi, Alireza Nazeri and Gangbing Song

Sensors 2012, 12(1), 1002-1013; https://doi.org/10.3390/s120101002 - 17 Jan 2012

Cited by 28 | Viewed by 8677

Abstract

Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, [...] Read more.

Atrial fibrillation (AF) is the most common type of arrhythmia, and is characterized by a disordered contractile activity of the atria (top chambers of the heart). A popular treatment for AF is radiofrequency (RF) ablation. In about 2.4% of cardiac RF ablation procedures, the catheter is accidently pushed through the heart wall due to the application of excessive force. Despite the various capabilities of currently available technology, there has yet to be any data establishing how cardiac perforation can be reliably predicted. Thus, two new FBG based sensor prototypes were developed to monitor contact levels and predict perforation. Two live sheep were utilized during the study. It was observed during operation that peaks appeared in rhythm with the heart rate whenever firm contact was made between the sensor and the endocardial wall. The magnitude of these peaks varied with pressure applied by the operator. Lastly, transmural perforation of the left atrial wall was characterized by a visible loading phase and a rapid signal drop-off correlating to perforation. A possible pre-perforation signal was observed for the epoxy-based sensor in the form of a slight signal reversal (12–26% of loading phase magnitude) prior to perforation (occurring over 8 s). Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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1070 KiB

Open AccessArticle

An Intrinsic Fiber-Optic Single Loop Micro-Displacement Sensor

by Alejandro Martinez-Rios, David Monzon-Hernandez, Ismael Torres-Gomez and Guillermo Salceda-Delgado

Sensors 2012, 12(1), 415-428; https://doi.org/10.3390/s120100415 - 4 Jan 2012

Cited by 13 | Viewed by 7878

Abstract

A micro-displacement sensor consisting of a fiber-loop made with a tapered fiber is reported. The sensor operation is based on the interaction between the fundamental cladding mode propagating through the taper waist and higher order cladding modes excited when the taper is deformed [...] Read more.

A micro-displacement sensor consisting of a fiber-loop made with a tapered fiber is reported. The sensor operation is based on the interaction between the fundamental cladding mode propagating through the taper waist and higher order cladding modes excited when the taper is deformed to form a loop. As a result, a transmission spectrum with several notches is observed, where the notch wavelength resonances shift as a function of the loop diameter. The loop diameter is varied by the spatial displacement of one end of the fiber-loop attached to a linear translation stage. In a displacement range of 3.125 mm the maximum wavelength shift is 360.93 nm, with 0.116 nm/μm sensitivity. By using a 1,280 nm broadband low-power LED source and a single Ge-photodetector in a power transmission sensor setup, a sensitivity in the order of 2.7 nW/μm is obtained in ~1 mm range. The proposed sensor is easy to implement and has a plenty of room to improve its performance. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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2571 KiB

Open AccessArticle

Dynamic Sensing Performance of a Point-Wise Fiber Bragg Grating Displacement Measurement System Integrated in an Active Structural Control System

by Kuo-Chih Chuang, Heng-Tseng Liao and Chien-Ching Ma

Sensors 2011, 11(12), 11605-11628; https://doi.org/10.3390/s111211605 - 13 Dec 2011

Cited by 7 | Viewed by 9819

Abstract

In this work, a fiber Bragg grating (FBG) sensing system which can measure the transient response of out-of-plane point-wise displacement responses is set up on a smart cantilever beam and the feasibility of its use as a feedback sensor in an active structural [...] Read more.

In this work, a fiber Bragg grating (FBG) sensing system which can measure the transient response of out-of-plane point-wise displacement responses is set up on a smart cantilever beam and the feasibility of its use as a feedback sensor in an active structural control system is studied experimentally. An FBG filter is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. For comparison, a laser Doppler vibrometer (LDV) is utilized simultaneously to verify displacement detection ability of the FBG sensing system. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is used to provide full-field vibration mode shapes and resonant frequencies. To verify the dynamic demodulation performance of the FBG filter, a traditional FBG strain sensor calibrated with a strain gauge is first employed to measure the dynamic strain of impact-induced vibrations. Then, system identification of the smart cantilever beam is performed by FBG strain and displacement sensors. Finally, by employing a velocity feedback control algorithm, the feasibility of integrating the proposed FBG displacement sensing system in a collocated feedback system is investigated and excellent dynamic feedback performance is demonstrated. In conclusion, our experiments show that the FBG sensor is capable of performing dynamic displacement feedback and/or strain measurements with high sensitivity and resolution. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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384 KiB

Open AccessArticle

Magnetic Field Measurements Based on Terfenol Coated Photonic Crystal Fibers

by Sully M. M. Quintero, Cicero Martelli, Arthur M. B. Braga, Luiz C. G. Valente and Carla C. Kato

Sensors 2011, 11(12), 11103-11111; https://doi.org/10.3390/s111211103 - 28 Nov 2011

Cited by 45 | Viewed by 8900

Abstract

A magnetic field sensor based on the integration of a high birefringence photonic crystal fiber and a composite material made of Terfenol particles and an epoxy resin is proposed. An in-fiber modal interferometer is assembled by evenly exciting both eigenemodes of the HiBi [...] Read more.

A magnetic field sensor based on the integration of a high birefringence photonic crystal fiber and a composite material made of Terfenol particles and an epoxy resin is proposed. An in-fiber modal interferometer is assembled by evenly exciting both eigenemodes of the HiBi fiber. Changes in the cavity length as well as the effective refractive index are induced by exposing the sensor head to magnetic fields. The magnetic field sensor has a sensitivity of 0.006 (nm/mT) over a range from 0 to 300 mT with a resolution about ±1 mT. A fiber Bragg grating magnetic field sensor is also fabricated and employed to characterize the response of Terfenol composite to the magnetic field. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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499 KiB

Open AccessArticle

Calibrating Single-Ended Fiber-Optic Raman Spectra Distributed Temperature Sensing Data

by Mark B. Hausner, Francisco Suárez, Kenneth E. Glander, Nick van de Giesen, John S. Selker and Scott W. Tyler

Sensors 2011, 11(11), 10859-10879; https://doi.org/10.3390/s111110859 - 21 Nov 2011

Cited by 203 | Viewed by 17440

Abstract

Hydrologic research is a very demanding application of fiber-optic distributed temperature sensing (DTS) in terms of precision, accuracy and calibration. The physics behind the most frequently used DTS instruments are considered as they apply to four calibration methods for single-ended DTS installations. The [...] Read more.

Hydrologic research is a very demanding application of fiber-optic distributed temperature sensing (DTS) in terms of precision, accuracy and calibration. The physics behind the most frequently used DTS instruments are considered as they apply to four calibration methods for single-ended DTS installations. The new methods presented are more accurate than the instrument-calibrated data, achieving accuracies on the order of tenths of a degree root mean square error (RMSE) and mean bias. Effects of localized non-uniformities that violate the assumptions of single-ended calibration data are explored and quantified. Experimental design considerations such as selection of integration times or selection of the length of the reference sections are discussed, and the impacts of these considerations on calibrated temperatures are explored in two case studies. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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2127 KiB

Open AccessArticle

Brillouin Corrosion Expansion Sensors for Steel Reinforced Concrete Structures Using a Fiber Optic Coil Winding Method

by Xuefeng Zhao, Peng Gong, Guofu Qiao, Jie Lu, Xingjun Lv and Jinping Ou

Sensors 2011, 11(11), 10798-10819; https://doi.org/10.3390/s111110798 - 16 Nov 2011

Cited by 86 | Viewed by 12477

Abstract

In this paper, a novel kind of method to monitor corrosion expansion of steel rebars in steel reinforced concrete structures named fiber optic coil winding method is proposed, discussed and tested. It is based on the fiber optical Brillouin sensing technique. Firstly, a [...] Read more.

In this paper, a novel kind of method to monitor corrosion expansion of steel rebars in steel reinforced concrete structures named fiber optic coil winding method is proposed, discussed and tested. It is based on the fiber optical Brillouin sensing technique. Firstly, a strain calibration experiment is designed and conducted to obtain the strain coefficient of single mode fiber optics. Results have shown that there is a good linear relationship between Brillouin frequency and applied strain. Then, three kinds of novel fiber optical Brillouin corrosion expansion sensors with different fiber optic coil winding packaging schemes are designed. Sensors were embedded into concrete specimens to monitor expansion strain caused by steel rebar corrosion, and their performance was studied in a designed electrochemical corrosion acceleration experiment. Experimental results have shown that expansion strain along the fiber optic coil winding area can be detected and measured by the three kinds of sensors with different measurement range during development the corrosion. With the assumption of uniform corrosion, diameters of corrosion steel rebars were obtained using calculated average strains. A maximum expansion strain of 6,738 με was monitored. Furthermore, the uniform corrosion analysis model was established and the evaluation formula to evaluate mass loss rate of steel rebar under a given corrosion rust expansion rate was derived. The research has shown that three kinds of Brillouin sensors can be used to monitor the steel rebar corrosion expansion of reinforced concrete structures with good sensitivity, accuracy and monitoring range, and can be applied to monitor different levels of corrosion. By means of this kind of monitoring technique, quantitative corrosion expansion monitoring can be carried out, with the virtues of long durability, real-time monitoring and quasi-distribution monitoring. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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597 KiB

Open AccessArticle

A Comparison of Delayed Self-Heterodyne Interference Measurement of Laser Linewidth Using Mach-Zehnder and Michelson Interferometers

by Albert Canagasabey, Andrew Michie, John Canning, John Holdsworth, Simon Fleming, Hsiao-Chuan Wang and Mattias L. Åslund

Sensors 2011, 11(10), 9233-9241; https://doi.org/10.3390/s111009233 - 27 Sep 2011

Cited by 21 | Viewed by 9528

Abstract

Linewidth measurements of a distributed feedback (DFB) fibre laser are made using delayed self heterodyne interferometry (DHSI) with both Mach-Zehnder and Michelson interferometer configurations. Voigt fitting is used to extract and compare the Lorentzian and Gaussian linewidths and associated sources of noise. The [...] Read more.

Linewidth measurements of a distributed feedback (DFB) fibre laser are made using delayed self heterodyne interferometry (DHSI) with both Mach-Zehnder and Michelson interferometer configurations. Voigt fitting is used to extract and compare the Lorentzian and Gaussian linewidths and associated sources of noise. The respective measurements are w_L (MZI) = (1.6 ± 0.2) kHz and w_L (MI) = (1.4 ± 0.1) kHz. The Michelson with Faraday rotator mirrors gives a slightly narrower linewidth with significantly reduced error. This is explained by the unscrambling of polarisation drift using the Faraday rotator mirrors, confirmed by comparing with non-rotating standard gold coated fibre end mirrors. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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456 KiB

Open AccessArticle

Power Loss Characteristics of a Sensing Element Based on a Polymer Optical Fiber under Cyclic Tensile Elongation

by Yung-Chuan Chen, Li-Wen Chen and Wei-Hua Lu

Sensors 2011, 11(9), 8741-8750; https://doi.org/10.3390/s110908741 - 8 Sep 2011

Cited by 7 | Viewed by 7516

Abstract

In this study, power losses in polymer optical fiber (POF) subjected to cyclic tensile loadings are studied experimentally. The parameters discussed are the cyclic load level and the number of cycles. The results indicate that the power loss in POF specimens increases with [...] Read more.

In this study, power losses in polymer optical fiber (POF) subjected to cyclic tensile loadings are studied experimentally. The parameters discussed are the cyclic load level and the number of cycles. The results indicate that the power loss in POF specimens increases with increasing load level or number of cycles. The power loss can reach as high as 18.3% after 100 cyclic loadings. Based on the experimental results, a linear equation is proposed to estimate the relationship between the power loss and the number of cycles. The difference between the estimated results and the experimental results is found to be less than 3%. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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301 KiB

Open AccessArticle

Remote (250 km) Fiber Bragg Grating Multiplexing System

by Montserrat Fernandez-Vallejo, Sergio Rota-Rodrigo and Manuel Lopez-Amo

Sensors 2011, 11(9), 8711-8720; https://doi.org/10.3390/s110908711 - 8 Sep 2011

Cited by 33 | Viewed by 9558

Abstract

We propose and demonstrate two ultra-long range fiber Bragg grating (FBG) sensor interrogation systems. In the first approach four FBGs are located 200 km from the monitoring station and a signal to noise ratio of 20 dB is obtained. The second improved version [...] Read more.

We propose and demonstrate two ultra-long range fiber Bragg grating (FBG) sensor interrogation systems. In the first approach four FBGs are located 200 km from the monitoring station and a signal to noise ratio of 20 dB is obtained. The second improved version is able to detect the four multiplexed FBGs placed 250 km away, offering a signal to noise ratio of 6–8 dB. Consequently, this last system represents the longest range FBG sensor system reported so far that includes fiber sensor multiplexing capability. Both simple systems are based on a wavelength swept laser to scan the reflection spectra of the FBGs, and they are composed by two identical-lengths optical paths: the first one intended to launch the amplified laser signal by means of Raman amplification and the other one is employed to guide the reflection signal to the reception system. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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494 KiB

Open AccessArticle

Effect of Coating on the Strain Transfer of Optical Fiber Sensors

by Shiuh-Chuan Her and Chih-Ying Huang

Sensors 2011, 11(7), 6926-6941; https://doi.org/10.3390/s110706926 - 1 Jul 2011

Cited by 132 | Viewed by 10968

Abstract

Optical fiber strain sensors with light weight, small dimensions and immunity to electromagnetic interference are widely used in structural health monitoring devices. As a sensor, it is expected that the strains between the optical fiber and host structure are the same. However, due [...] Read more.

Optical fiber strain sensors with light weight, small dimensions and immunity to electromagnetic interference are widely used in structural health monitoring devices. As a sensor, it is expected that the strains between the optical fiber and host structure are the same. However, due to the shear deformation of the protective coating, the optical fiber strain is different from that of host structure. To improve the measurement accuracy, the strain measured by the optical fiber needs to be modified to reflect the influence of the coating. In this investigation, a theoretical model of the strain transferred from the host material to the optical fiber is developed to evaluate the interaction between the host material and coating. The theoretical predictions are validated with a numerical analysis using the finite element method. Experimental tests are performed to reveal the differential strains between the optical fiber strain sensor and test specimen. The Mach-Zehnder interferometric type fiber-optic sensor is adopted to measure the strain. Experimental results show that the strain measured at the optical fiber is lower than the true strain in the test specimen. The percentage of strain in the test specimen actually transferred to the optical fiber is dependent on the bonded length of the optical fiber and the protective coating. The general trend of the strain transformation obtained from both experimental tests and theoretical predictions shows that the longer the bonded length and the stiffer the coating the more strain is transferred to the optical fiber. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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Review

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1067 KiB

Open AccessReview

Fiber-Optical Sensors: Basics and Applications in Multiphase Reactors

by Xiangyang Li, Chao Yang, Shifang Yang and Guozheng Li

Sensors 2012, 12(9), 12519-12544; https://doi.org/10.3390/s120912519 - 13 Sep 2012

Cited by 39 | Viewed by 13876

Abstract

This work presents a brief introduction on the basics of fiber-optical sensors and an overview focused on the applications to measurements in multiphase reactors. The most commonly principle utilized is laser back scattering, which is also the foundation for almost all current probes [...] Read more.

This work presents a brief introduction on the basics of fiber-optical sensors and an overview focused on the applications to measurements in multiphase reactors. The most commonly principle utilized is laser back scattering, which is also the foundation for almost all current probes used in multiphase reactors. The fiber-optical probe techniques in two-phase reactors are more developed than those in three-phase reactors. There are many studies on the measurement of gas holdup using fiber-optical probes in three-phase fluidized beds, but negative interference of particles on probe function was less studied. The interactions between solids and probe tips were less studied because glass beads etc. were always used as the solid phase. The vision probes may be the most promising for simultaneous measurements of gas dispersion and solids suspension in three-phase reactors. Thus, the following techniques of the fiber-optical probes in multiphase reactors should be developed further: (1) online measuring techniques under nearly industrial operating conditions; (2) corresponding signal data processing techniques; (3) joint application with other measuring techniques. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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542 KiB

Open AccessReview

Recent Progress in Distributed Fiber Optic Sensors

by Xiaoyi Bao and Liang Chen

Sensors 2012, 12(7), 8601-8639; https://doi.org/10.3390/s120708601 - 26 Jun 2012

Cited by 1215 | Viewed by 35496

Abstract

Rayleigh, Brillouin and Raman scatterings in fibers result from the interaction of photons with local material characteristic features like density, temperature and strain. For example an acoustic/mechanical wave generates a dynamic density variation; such a variation may be affected by local temperature, strain, [...] Read more.

Rayleigh, Brillouin and Raman scatterings in fibers result from the interaction of photons with local material characteristic features like density, temperature and strain. For example an acoustic/mechanical wave generates a dynamic density variation; such a variation may be affected by local temperature, strain, vibration and birefringence. By detecting changes in the amplitude, frequency and phase of light scattered along a fiber, one can realize a distributed fiber sensor for measuring localized temperature, strain, vibration and birefringence over lengths ranging from meters to one hundred kilometers. Such a measurement can be made in the time domain or frequency domain to resolve location information. With coherent detection of the scattered light one can observe changes in birefringence and beat length for fibers and devices. The progress on state of the art technology for sensing performance, in terms of spatial resolution and limitations on sensing length is reviewed. These distributed sensors can be used for disaster prevention in the civil structural monitoring of pipelines, bridges, dams and railroads. A sensor with centimeter spatial resolution and high precision measurement of temperature, strain, vibration and birefringence can find applications in aerospace smart structures, material processing, and the characterization of optical materials and devices. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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986 KiB

Open AccessReview

Fiber Sensor Systems Based on Fiber Laser and Microwave Photonic Technologies

by Hongyan Fu, Daru Chen and Zhiping Cai

Sensors 2012, 12(5), 5395-5419; https://doi.org/10.3390/s120505395 - 27 Apr 2012

Cited by 31 | Viewed by 9971

Abstract

Fiber-optic sensors, especially fiber Bragg grating (FBG) sensors are very attractive due to their numerous advantages over traditional sensors, such as light weight, high sensitivity, cost-effectiveness, immunity to electromagnetic interference, ease of multiplexing and so on. Therefore, fiber-optic sensors have been intensively studied [...] Read more.

Fiber-optic sensors, especially fiber Bragg grating (FBG) sensors are very attractive due to their numerous advantages over traditional sensors, such as light weight, high sensitivity, cost-effectiveness, immunity to electromagnetic interference, ease of multiplexing and so on. Therefore, fiber-optic sensors have been intensively studied during the last several decades. Nowadays, with the development of novel fiber technology, more and more newly invented fiber technologies bring better and superior performance to fiber-optic sensing networks. In this paper, the applications of some advanced photonic technologies including fiber lasers and microwave photonic technologies for fiber sensing applications are reviewed. FBG interrogations based on several kinds of fiber lasers, especially the novel Fourier domain mode locking fiber laser, have been introduced; for the application of microwave photonic technology, examples of microwave photonic filtering utilized as a FBG sensing interrogator and microwave signal generation acting as a transversal loading sensor have been given. Both theoretical analysis and experimental demonstrations have been carried out. The comparison of these advanced photonic technologies for the applications of fiber sensing is carried out and important issues related to the applications have been addressed and the suitable and potential application examples have also been discussed in this paper. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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402 KiB

Open AccessReview

Optical Fiber Networks for Remote Fiber Optic Sensors

by Montserrat Fernandez-Vallejo and Manuel Lopez-Amo

Sensors 2012, 12(4), 3929-3951; https://doi.org/10.3390/s120403929 - 26 Mar 2012

Cited by 59 | Viewed by 9873

Abstract

This paper presents an overview of optical fiber sensor networks for remote sensing. Firstly, the state of the art of remote fiber sensor systems has been considered. We have summarized the great evolution of these systems in recent years; this progress confirms that [...] Read more.

This paper presents an overview of optical fiber sensor networks for remote sensing. Firstly, the state of the art of remote fiber sensor systems has been considered. We have summarized the great evolution of these systems in recent years; this progress confirms that fiber-optic remote sensing is a promising technology with a wide field of practical applications. Afterwards, the most representative remote fiber-optic sensor systems are briefly explained, discussing their schemes, challenges, pros and cons. Finally, a synopsis of the main factors to take into consideration in the design of a remote sensor system is gathered. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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702 KiB

Open AccessReview

Interferometric Fiber Optic Sensors

by Byeong Ha Lee, Young Ho Kim, Kwan Seob Park, Joo Beom Eom, Myoung Jin Kim, Byung Sup Rho and Hae Young Choi

Sensors 2012, 12(3), 2467-2486; https://doi.org/10.3390/s120302467 - 23 Feb 2012

Cited by 603 | Viewed by 32367

Abstract

Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms [...] Read more.

Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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867 KiB

Open AccessReview

Fiber Bragg Grating Sensors for Harsh Environments

by Stephen J. Mihailov

Sensors 2012, 12(2), 1898-1918; https://doi.org/10.3390/s120201898 - 10 Feb 2012

Cited by 730 | Viewed by 30054

Abstract

Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature [...] Read more.

Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This paper will present a review of some of the more recent developments. Full article

(This article belongs to the Special Issue Optical Fiber Sensors 2012)

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