Detection of defects and damages due to aging and transient events are important contributors to pipeline accidents and monitoring them together is challenging. In this work, we demonstrate an intelligent fiber-optic acoustic sensor system for pipeline monitoring that enables real-time recognition, and classification of defects and transient threats together by analyzing the combined acoustic NDE data from the ultrasonic guidedwaves and acoustic emission methods. A 6"carbon-steel pipeline (16-ft long, SCH40) having multiple structural defects (weld and corrosion) is used with multiplexed optical fiber sensors as acoustic receivers attached to the pipe for ultrasonic GW monitoring to identifying structural defects and transient event (intrusion and impact) detection by the spontaneous acoustic emission method. Finally, we discussed our strategy to apply the convolutional neural network (CNN) model to the acoustic NDE data obtained by two methods to realize an accurate and automated pipeline health monitoring solution.
Current ultrasonic acoustic NDE methods for long distance inspection in cylindrical structures are primarily focused on axisymmetric guided waves excitation. However, there are many occasions where the physical limitations imposed by the system to be inspected restrain the ability to utilize equipment capable of exciting those waves. This study explores the excitation of the flexural guided wave modes by a limited number of piezoelectric transducers for damage detection in hollow cylinders with limited surface access and large diameter. In addition, the use of distributed optical fiber system as the guided wave receptor is investigated as an alternative to piezoelectric transducers (PZT), as their capability to acquire spatial-temporal data synergizes with the complexity in a signal containing several flexural GW modes. More specifically, the study is conducted based on a numerical analysis of the guided waves excited by a 2 PZT configuration in a pipe available for experimental testing. The resulting flexural modes and its interaction with welds and local loss of material are analyzed in terms of the time series data of a local sensor in the surface, and the angular profile differences from a healthy case. A method based on the analytical solution of an infinite cylinder is introduced in preliminary stage to extract the behavior of the dominant modes from simulation and experimental results and used as a simulation-experiment similarity comparison. Finally, a simplified convolutional neural network (CNN) is trained to demonstrate feasibility of using flexural modes excited by limited actuators for damage detection. Overall, this study contributes to the development of a damage detection method applicable to cylindrical structures with dimensional and access limitations, by enhancing the understanding of how simultaneous several flexural modes interact with mechanical features, presenting an early-stage interpretable method to compare simulation and experimental fiber optic sensor data, and demonstrating the feasibility of using DAS like data for analyzing the structure.
This paper examines the efficacy of quasi-distributed acoustic sensors (q-DAS) in identifying damage within pipeline structures, placing a substantial emphasis on generating synthetic q-DAS measurements in active ultrasonic testing setting and bridging the gap between synthetic and real q-DAS measurements. Our research utilizes simulation software to model the ultrasonic guided wave propagation and its interaction with pipeline defects. The pipeline structural health monitoring setup is based on the pulse-echo method utilizing a torsional symmetric mode T(0,1) at 32kHz, with an aim to identify corrosion and weld irregularities over extensive pipeline lengths. We have prioritized the calibration of simulation models against experimental data, fine-tuning the simulation processes to reflect actual conditions with higher fidelity. The study specifically highlights the simulation’s accuracy in capturing the distinct signatures of critical pipeline features and the subsequent detection capabilities within an operational context. By focusing on the experimental validation, we have advanced the understanding and application of structural health monitoring for essential infrastructure, ensuring the simulations' predictive strength aligns closely with real-world sensor data and observed phenomena.
Structural Health Monitoring (SHM) of pipelines using nondestructive testing/evaluation (NDT/E) techniques is important particularly for the energy industries and for the oil/gas distribution which helps reduction in maintenance costs as well as increased service lifespan. Among various NDE techniques, ultrasonic guidedwaves (GWs) technique is popular for inspection and monitoring of pipes due to its advantages e.g., long-distance monitoring using a fixed sensor probe, full volumetric coverage, and inspection for invisible or inaccessible structure. Recently, performance and scope of the GWs method is explored using optical fiber sensing technology such as fiber Bragg gratings are demonstrated for many ultrasonic sensing applications. The optical fiber sensors bring the advantage of remote sensing, large acoustic bandwidth, and multiplexing capability of the sensors to extend the range of GWs based NDE method. This work describes the health monitoring of damaged pipeline structure in a nondestructive manner using alternative No-core fiber (NCF) based quasi-distributed fiber-optic acoustic sensor combined with ultrasonic GWs excitation. We set up two similar 6-inch carbon-steel pipes (16-ft long), one consists of various defects and the other is healthy without any defect for reference. The pipes are actively excited by employing different ultrasonic sources; (1) magnetostrictive collar (MR) to generate the axisymmetric (torsion) GWs and (2) conventional piezoelectric patches to generate the antisymmetric flexural waves on the exterior surface, and the characteristics of acoustic-ultrasonic signals are studied using NCF based multiplexed fiber-optic sensor. Fiber optic sensor is an inline multimode interferometer made by sandwiching a piece of NCF (~5cm) between the single mode fibers. The NCF sensor is remotely bonded at 45° w.r.t pipe axis on one end and has an ultrasonic sensing range of >600kHz. Finally, the measured acousto-ultrasonic signals for different ultrasonic sources are compared to those obtained by the numerical simulation or electrical-based sensor for the healthy and damaged test pipes. The proposed work presents useful insight for damage detection in pipes using an NCF-based quasi-distributed fiber-optic acoustic sensor combined with ultrasonic GWs excitation.
The cost of conventional fiber optic interrogation system has been the limiting factor for its commercialization and market penetration into electrical asset monitoring where the room for capital investment on sensors is relatively small. The ability to deliver portable and cost-effective sensors without compromising their performances becomes critical. Here, we demonstrate the application and low-cost interrogation strategy for intensity-modulated evanescent wave fiber temperature sensor made of plasmonenabled thin films. Optical transmittance change resulting from the thermal damping of plasmonic absorption intensity is converted into analog voltage signals, then transmitted wirelessly through a set of commercial wireless hardware to enable remote monitoring capability. The temperature response is compared against a custom-designed intensity-based Fiber Bragg Grating (FBG) interrogator with Long Period Grating (LPG) edge filter, where its temperature and strain sensing performance of the intensity-based FBG interrogator is presented and discussed. Both sensors are deployed to monitor the dynamic thermal behavior of Li-ion polymer pouch cell under normal charging/discharging conditions. Finally, the initial design and implementation of an energy harvesting circuit that powers the low-cost wireless interrogator from a potential instrumented power conversion/storage device itself is also discussed.
Even though the dynamic response of the magnetic fluid is well investigated by magnetic means and known for their high frequency response in MHz to GHz range, the same has not been explored as much by optical means in the context of optical fiber sensor platform. The use of magnetic fluid as sensing materials in various fiber optic senor platform is limited to DC magnetic field sensing. In this work, we present the results of magnetic fluid functionalized multimode interferometric fiber optic sensors for their efficacy in measuring the dynamic current induced magnetic field and their limitations to AC frequency response imposed by optical spectrometer as interrogator unit, the response time of the sensing material and the sensor itself. The interferometric structure optimized for unique narrow linewidth spectral response, also known as “fourth self-imaging” in fiber optic platform has demonstrated response time to ~15ms enabling sensing of AC magnetic field and measured up to 10Hz sinusoidal H-field within the peak-to-peak applied H-field of 30Gauss. By further tailoring of magnetic nanoparticle’s concentration in ferrofluid, it is anticipated that the sensors frequency response can be pushed to higher frequencies. The study extends the versatility of these magnetic field sensitive materials for their applications to AC-current and magnetic field sensing.
Fiber optic sensors show many advantages as compared to other alternatives for a wide range of energy applications spanning electrical grid, pipelines, and civil infrastructure monitoring amongst others. Multimode interference-based fiber optic sensor configuration is one device architecture that is being explored for a range of different analytes, and which is fabricated by sandwiching a section of multimode fiber between two single mode fibers. Fiber optic devices based on multimode interference (MMI) are easy to fabricate and offer attractive prospects for applications in the areas of optical communication and fiber lasers as well as sensing. When light is coupled from a single mode fiber to a multimode fiber (MMF), multiple modes supported by the MMF are excited and interfere with each other, giving rise to an interference pattern along the MMF length. At specific positions along the axis of the MMF, light is concentrated and forms replicas of the input field which are known as self-images, with the self-imaging condition providing a narrow-band interference feature as a function of wavelength that is also affected by a wide range of analytes for sensing purposes. The self-images formed are simulated here using commercial software COMSOL Multiphysics. Sensitivity to a range of different analytes including refractive index, strain and hydrogen gas is explored. Optical fiber sensors based upon multimode interferometer sensors are investigated as attractive sensing options for infrastructure monitoring applications.
Electrical system monitoring applications are of increasing importance given recent trends towards electrification driving adoption of renewables and electric vehicles, for example. Thermal and acoustic signatures play an important role in health monitoring while electrical and magnetic field signatures can provide information about operational state. Optical fiber sensors are of particular interest for electrical system applications because of the compatibility with deployment in electrified systems without concerns for electromagnetic interference (EMI) or additional potential risks due to the presence of electrical sensor wires or power at the sensing location, particularly for medium voltage electrical systems. In this presentation, an overview of recent work in optical fiber-based sensing for electrical asset monitoring applications will be discussed in detail. Plasmonic sensors integrated with engineered nanomaterials will be discussed for thermal and other health monitoring applications while interferometric sensors will be discussed for acoustics and also magnetic fields and electrical current sensing. New directions in fiber-based sensing applications will also be discussed moving into the future.
In this paper, we field demonstrate a natural gas pipeline monitoring based on optical frequency domain reflectometry (OFDR). OFDR can monitor distributed temperature and strain measurements along the natural gas pipelines and provide valuable information about pipe structural health, like hoop strain changes caused by pipe wall thinning or temperature changes from gas leaks based on Joule-Thomson effect. Distributed temperature and strain measurements were demonstrated where the pipeline operated at various pressure levels. The static pressure-induced hoop strain in a pilot-scale field test in a natural gas flowing high-pressure loop. The pilot scale testing results demonstrated in this paper indicate that the OFDR system is a promising tool for real-time monitoring of a pipeline without influence on normal operating conditions of the gas pipeline.
Optical fiber based electro-magnetic field sensors is a diverse and expanding field in fiber sensor technology with applications spanning from geomagnetism, biomagnetism, nuclear magnetism to safety and operational monitoring of power grid systems. Particularly, because of the dielectric silica material of the fiber that provides high electric insulation and immunity to the electromagnetic interference (EMI), a major reason contributing to the limitations in conventional sensors, the efforts have been focused on developing the fiber-optic sensors with increased sensitivity, bandwidth, and detection range specific to an application but all benefit from the advantages of the platform. Various fiber structures, interrogation schemes and sensing materials have been investigated. One major interest is on the fiber-optic sensor based on multi-mode interference (MMI) where a multimode mode fiber is fusion spliced between two single mode fibers also known as SMS (single-mode/multimode/single mode) fiber sensor. Ease of fabrication, compactness, higher sensitivity, and low cost are some of the driving factors in addition to the potential for direct integration of the platform with functional sensor materials to tailor for specific applications. For the purpose of magnetic field sensing, the magnetic fluid is the most widely used functional material as the sensing/cladding layer on the fiber-structure. Here we present efforts to enhance and optimize the sensitivity of such SMS structure with magnetic fluid as the sensing material exploiting the unique “self-imaging” property of the SMS sensor where the sensor produces a filterlike spectral response and is highly sensitive to the change in magneto-optical property of surrounding medium. The performance metrics of the sensor are analyzed against DC magnetic field range keeping an eye in detecting typical current induced magnetic field in power grid systems.
Absence of a final repository for nuclear waste has increased attention on dry cask storage systems (DCSSs) which were originally intended for temporary storage, increasing the need for new structural health monitoring paradigms considering safety and environmental impacts. Current integrity inspection requirements consist of periodic manned inspections due in part to the difficulties with real-time monitoring of internal canister conditions without penetrating the canister surface. Here we overview a new approach to nuclear canister integrity structural health monitoring which combines both quasi-distributed fiber optic acoustic (and other) sensing modalities deployed external to the canister as well as physics-based modeling to enable real-time inference of internal canister conditions, including the identification, localization, and classification of various active or incipient failure conditions. More specifically, we overview the vision for the proposed monitoring approach and describe results to date in theoretical physics-based modeling and artificial intelligence-based analytics to accelerate the development of classification frameworks for rapid interpretation of quasi-distributed acoustic and other complementary fiber optic sensing responses. In addition, we describe early results obtained for a quasi-distributed fiber optic sensor network based upon multimode interferometer sensors using an experimental test bed established for dry-cask storage canister sensing experiments. Future work will be overviewed and discussed in the context of expanded scope of the proposed real-time monitoring system and planned field validations.
KEYWORDS: Signal to noise ratio, Acoustics, Optical fibers, Metals, Single mode fibers, Optical sensing, Ferroelectric materials, Structural health monitoring, Fiber optics sensors, Data acquisition
Pipeline infrastructure monitoring based on distributed fiber-optic acoustic sensing is gaining significant attention aimed at real-time rapid detection of leakages, third-party intrusion, geo-hazards, corrosion, and other structural damages. Typical fibers installations are external to a pipeline, however retrofitting of existing pipelines through internal installation is desirable despite deployment challenges. Highly sensitive distributed acoustic sensing integrated within new pipelines or retrofit in existing pipelines can enable early detection of damage and degradation. In this work, we demonstrate pipeline integrity monitoring using distributed acoustic sensing and the Rayleigh backscattering-enhanced optical fibers deployed internal to the pipeline for high sensitivity detection of acoustic events. More specifically, traditional and backscattering-enhanced optical fibers are interrogated using bench-top phase-sensitive optical time-domain reflectometry (Φ-OTDR). The distributed acoustic sensing characteristics of two types of backscattered-enhanced fibers, Type A and Type B, are experimentally investigated. Our measurement analysis shows that the SNR of the acoustic event detection enhances ~2-fold and ~3-fold using the Type A and Type B fiber, respectively than that of the traditional SMF for pipeline monitoring. The presented investigation is a first validation for in-pipe deployed distributed acoustic sensing with high SNR and provides useful insight for diverse pipeline monitoring applications in the oil and gas distribution industry.
In this study, highly Dy3+-doped germano-borate glasses for different dopant concentrations ranging from 20 to 30 mol% were fabricated and their physical, optical, and MO properties were investigated. The characteristic thermal parameters disclosed good thermal stability of <100 °C against crystallization in the studied glasses. In addition, the glasses showed a high optical transmission of ~ 85% in the NIR region of 1550 nm. A very large Verdet constant of approximately -5.36 rad/(T·m) at 1550 nm was obtained in the glass containing 30 mol% Dy2O3. Therefore, this glass might be a promising MO material for applications in the NIR region.
KEYWORDS: Signal to noise ratio, Spatial resolution, Fiber Bragg gratings, Data acquisition, Signal processing, Composites, Reflectometry, Signal detection, Optical fibers, Structural health monitoring
We demonstrate a distributed localization of an impact source in the composite cylinder using a home-made phase sensitive optical time domain reflectometer (Φ-OTDR). The system shows the advantages of simple configuration using semiconductor optical amplifier to improve the spectral response of the pump pulses, high spatial resolution and high signal-to-noise ratio (SNR). With a spatial resolution of 10 m, the SNR could be obtained as high as 6.5 dB. A composite cylinder is longitudinally divided in multiple sections of equal lengths by bending the sensing fibers around it at different locations, and the section of a source impact is localized using the time-delay of the signal detected by the sensing fibers.
KEYWORDS: Acoustics, Single mode fibers, Signal processing, Signal to noise ratio, Data acquisition, Signal detection, Reflectometry, Semiconductor lasers, Semiconductor optical amplifiers, Fiber Bragg gratings
We analyze the relations of parameters in moving average method to enhance the event detectability of phase sensitive optical time domain reflectometer (OTDR). If the external events have unique frequency of vibration, then the control parameters of moving average method should be optimized in order to detect these events efficiently. A phase sensitive OTDR was implemented by a pulsed light source, which is composed of a laser diode, a semiconductor optical amplifier, an erbium-doped fiber amplifier, a fiber Bragg grating filter, and a light receiving part, which has a photo-detector and high speed data acquisition system. The moving average method is operated with the control parameters: total number of raw traces, M, number of averaged traces, N, and step size of moving, n. The raw traces are obtained by the phase sensitive OTDR with sound signals generated by a speaker. Using these trace data, the relation of the control parameters is analyzed. In the result, if the event signal has one frequency, then the optimal values of N, n are existed to detect the event efficiently.
We experimentally demonstrated torsion sensing characteristics of a highly-birefringent asymmetric two-core photonic crystal fiber (HB-ATCPCF) in the Sagnac loop configuration. Two cores in the HB-ATCPCF exhibit distinct birefringence properties and light launched into them propagate with negligible coupling. The transmission interference spectrum of the device shows six frequency peaks in the spatial domain, which corresponds to the two Sagnac and four Mach-Zehnder interference spectra characterized by the four-beam interference model. Torsion response of the device was investigated by measuring the shift of the peak wavelength and the fringe visibility of the fiber interferences using fast Fourier transform-based spectrum-demodulation method.
We experimentally demonstrate a novel all-fiber Sagnac loop hybrid interferometer (SLHI) based on a highlybirefringent photonic crystal fiber with two asymmetric cores. Two cores exhibit unique birefringence properties and the light launched into them propagates with negligible coupling. Fast Fourier transform analysis of the transmission spectrum shows six frequency peaks in the spatial domain due to multiple interferences comprising the intra-core and inter-core mode interferences characterized by the four-beam interference model. The device response is investigated under the application of torsion, strain and temperature by measuring the phase-shift responses of three fiber interferences in the SLHI. The device application in simultaneous multi-parameter measurement is also discussed.
We propose and demonstrate a highly sensitive micro-fluidic temperature sensor based on a two-core photonic crystal fiber (TCPCF). TCPCF has two cores of small asymmetry in sizes that serves as two arms in the inline Mach-Zehnder interferometer (MZI). Using manual gluing and subsequent infiltration technique, the cladding air holes near one core are selectively filled with polymer of high thermo-optic coefficient, which makes its core-mode effective index sensitive to temperature variation and induces large thermo-optic mismatch between the two cores. A high sensitivity of 1.595 nm/ oC is achieved in our experiment, which is almost 200 times improved from that of the sensor device before polymer infiltration process.
We investigate the strain and temperature sensing characteristics of an inline hybrid Mach-Zehnder interferometer (HMZI) formed by splicing a short section of asymmetric twin-core photonic crystal fiber (ATC-PCF) between two single mode fibers. For fixed polarization state of input light, two cores due to their asymmetric construction strongly support the propagation of few dominant core-modes, specifically, a lowest-order, and a set of lowest- and higher-order core-modes, respectively; this leads to a unique phase difference between inter-core and intra-core mode fiber interferometers in our ATC-PCF based HMZI. Experimental results reveal that, among different orders of interferometers involved in the HMZI, the interferometer with higher-value of modal refractive index difference exhibit larger phase-shift sensitivity to the surrounding perturbations.
We propose and experimentally demonstrate a new chemical molecule sensing scheme using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber. In our proposed multi-wavelength fiber laser, two separated cores are integrated in a single photonic crystal fiber and surrounded by air channels. The anti-symmetrical super-modes participate in inter-core interference, which leads to the formation of twin-core photonic crystal fiber-based wavelength-selective comb filter. Most of the evanescent waves are localized in the 13 air channels around the two integrated cores, where light-matter interaction takes in place. The presence of chemical molecules in the air channels of TC-PCF leads to perturbation of the inter-core effective index difference between the two propagating core modes and the associated lasing wavelength shift.
An inline Mach-Zehnder interferometer (MZI) is demonstrated using liquid filled twin-core photonic crystal fiber (TCPCF).
The TC-PCF is filled selectively with liquid ethanol, increasing the effective refractive index contrast between
twin cores, resulting in interference fringe spectrum with narrower free spectral range (FSR). Strain induced wavelength
shift of the interference fringes is experimentally monitored. Wavelength shifts to the shorter wavelength side with a
sensitivity of about -1.48 pm/με for applied strain change. Selectively liquid filled TC-PCF based MZI is simple to
fabricate and expected to have wide range of applications in optical sensors, multi-wavelength laser source and tunable
optical devices.
This paper presents chemical vapor sensing properties of twin-core photonic crystal fiber-based in-reflection
interferometer. The interferometer is composed of end-cleaved twin-core photonic crystal fiber (TC-PCF) and fiber
circulator. Infiltrating chemical molecules in the air holes of TC-PCF lead to change in inter-core effective index
difference and associated fringe shift in the interferometer. As an example we demonstrate acetone vapor detection and
discuss the potential applications of the proposed device.
We fabricated asymmetric two-core photonic crystal fiber (AS-TC-PCF) and observed the temperature and strain
responses of the Michelson interferometer based on it. The asymmetric two cores induce optical path length difference
and produce polarization-dependent interference fringes. The temperature and strain sensitivities of the AS-TC-PCF
were measured using the interference fringe shift. With increasing temperature, the interference fringes shifted to longer
wavelengths, and the temperature sensitivities were measured to be 5.06 pm/°C and 11.05 pm/°C, respectively, for
different polarizations. However, with increasing strain, the interference fringes shifted to shorter wavelengths, and the
strain sensitivities were measured to be -0.50 pm/με and -1.87 pm/με, respectively.
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