Special Issue "Optical Fiber Sensors"
Quicklinks
A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".
Deadline for manuscript submissions: closed (15 January 2012)
Special Issue Editor
Guest Editor
Prof. Dr. Byeong Ha Lee
School of Information and Communications, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro, Buk-gu, Gwangju, 500-712, Korea
Website: http://aolab.gist.ac.kr/professor.html
E-Mail: leebh@gist.ac.kr
Interests: fabrication and characterization of fiber gratings; photonic crystal fibers (PCF); fiber-optic sensors and sensor systems; fiber interferometer; specialty fiber devices for sensor applications; fiber-based optical imaging systems
Special Issue Information
Dear Colleagues,
For the several decades, optical fibers have sharply revolutionized communication industries owing to their high performance. Not once as the high performance communication media, however, with the help of optoelectronic technology, optical fibers have been studied as novel and smart “Optical Fiber Sensors”. Unique beneficial characteristics such as wavelength multiplexing, low propagating loss, high sensing sensitivity, low fabrication cost, small form factor, and immunity to electromagnetic interference (EMI) have made optical fibers suitable for sensing various physical, chemical, and biological parameters. Furthermore, their sensing abilities have been widely improved by the advance of various fiber optic technologies like fiber gratings, fiber interferometers, Brillouin scattering, surface plasmon resonance, micro-structured fibers, nano-wires, etc. As a result, commercializing optical fiber sensors become great interest to many companies. have a in . It is expected that they will possess a big part of sensor market shortly. This special issue, “Optical Fiber Sensors”, will cover every possible fiber optic sensing techniques for every applicable field. Your contribution is most warmly expected and would be highly appreciated.
Prof. Dr. Byeong Ha Lee
Guest Editor
Submission
Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.
Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed Open Access monthly journal published by MDPI.
Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs).
Keywords
- fiber optic sensors
- fiber grating sensors
- photonic cystal fiber sensors
- smart structure sensors
- distributed sensors
- surface plasmonic sensors
- nano-wire sensors
- Brillouin sensors
- sensor systems
- sensor networks
- fiber interferometers
Published Papers (25 papers)
|
Received: 17 May 2011; in revised form: 27 June 2011 / Accepted: 27 June 2011 / Published: 1 July 2011
Show/Hide Abstract
| Download PDF Full-text (494 KB)
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 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.
|
|
Received: 4 July 2011; in revised form: 1 September 2011 / Accepted: 7 September 2011 / Published: 8 September 2011
Show/Hide Abstract
| Download PDF Full-text (301 KB)
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 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.
|
|
Received: 4 August 2011; in revised form: 29 August 2011 / Accepted: 1 September 2011 / Published: 8 September 2011
Show/Hide Abstract
| Download PDF Full-text (456 KB)
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 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%.
|
|
Received: 17 August 2011; in revised form: 13 September 2011 / Accepted: 23 September 2011 / Published: 27 September 2011
Show/Hide Abstract
| Download PDF Full-text (597 KB)
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 respective measurements are wL (MZI) = (1.6 ± 0.2) kHz and wL (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.
|
|
Received: 8 October 2011; in revised form: 10 November 2011 / Accepted: 12 November 2011 / Published: 16 November 2011
Show/Hide Abstract
| Download PDF Full-text (2127 KB)
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 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.
|
|
Received: 19 October 2011; in revised form: 15 November 2011 / Accepted: 16 November 2011 / Published: 21 November 2011
Show/Hide Abstract
| Download PDF Full-text (499 KB) | 
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 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.
|
|
Received: 25 October 2011; in revised form: 21 November 2011 / Accepted: 23 November 2011 / Published: 28 November 2011
Show/Hide Abstract
| Download PDF Full-text (384 KB)
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 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.
|
|
Received: 17 October 2011; in revised form: 28 November 2011 / Accepted: 3 December 2011 / Published: 13 December 2011
Show/Hide Abstract
| Download PDF Full-text (2571 KB)
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 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.
|
|
Received: 15 December 2011; in revised form: 26 December 2011 / Accepted: 28 December 2011 / Published: 4 January 2012
Show/Hide Abstract
| Download PDF Full-text (1070 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 25 November 2011; in revised form: 3 January 2012 / Accepted: 14 January 2012 / Published: 17 January 2012
Show/Hide Abstract
| Download PDF Full-text (696 KB) | View HTML Full-text | Download PMC-XML Full-text
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, 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).
|
|
Received: 16 January 2012; in revised form: 3 February 2012 / Accepted: 8 February 2012 / Published: 10 February 2012
Show/Hide Abstract
| Download PDF Full-text (867 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 19 January 2012; in revised form: 6 February 2012 / Accepted: 9 February 2012 / Published: 15 February 2012
Show/Hide Abstract
| Download PDF Full-text (648 KB) | View HTML Full-text | Download PMC-XML Full-text
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 (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.
|
|
Received: 16 January 2012; in revised form: 6 February 2012 / Accepted: 6 February 2012 / Published: 23 February 2012
Show/Hide Abstract
| Download PDF Full-text (702 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 11 January 2012; in revised form: 23 February 2012 / Accepted: 23 February 2012 / Published: 8 March 2012
Show/Hide Abstract
| Download PDF Full-text (1015 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 17 January 2012; in revised form: 28 February 2012 / Accepted: 7 March 2012 / Published: 12 March 2012
Show/Hide Abstract
| Download PDF Full-text (324 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 17 January 2012; in revised form: 24 February 2012 / Accepted: 14 March 2012 / Published: 16 March 2012
Show/Hide Abstract
| Download PDF Full-text (635 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 13 February 2012; in revised form: 14 March 2012 / Accepted: 14 March 2012 / Published: 26 March 2012
Show/Hide Abstract
| Download PDF Full-text (361 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 16 February 2012; in revised form: 28 February 2012 / Accepted: 5 March 2012 / Published: 26 March 2012
Show/Hide Abstract
| Download PDF Full-text (596 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 29 January 2012; in revised form: 1 March 2012 / Accepted: 15 March 2012 / Published: 26 March 2012
Show/Hide Abstract
| Download PDF Full-text (402 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 18 January 2012; in revised form: 7 March 2012 / Accepted: 26 March 2012 / Published: 28 March 2012
Show/Hide Abstract
| Download PDF Full-text (1358 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 16 January 2012; in revised form: 31 March 2012 / Accepted: 5 April 2012 / Published: 12 April 2012
Show/Hide Abstract
| Download PDF Full-text (1497 KB) | View HTML Full-text | Download PMC-XML Full-text
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 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.
|
|
Received: 17 March 2012; in revised form: 15 April 2012 / Accepted: 17 April 2012 / Published: 27 April 2012
Show/Hide Abstract
| Download PDF Full-text (1231 KB)
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 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.
|
|
Received: 14 March 2012; in revised form: 9 April 2012 / Accepted: 12 April 2012 / Published: 27 April 2012
Show/Hide Abstract
| Download PDF Full-text (986 KB)
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 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.
|
|
Received: 15 February 2012; in revised form: 10 April 2012 / Accepted: 16 April 2012 / Published: 27 April 2012
Show/Hide Abstract
| Download PDF Full-text (303 KB)
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 < 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.
|
|
Received: 5 April 2012; in revised form: 3 May 2012 / Accepted: 3 May 2012 / Published: 8 May 2012
Show/Hide Abstract
| Download PDF Full-text (835 KB)
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 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.
|
Last update: 23 March 2012
