This PDF file contains the front matter associated with SPIE Proceedings Volume 12105 including the Title Page, Copyright information, Table of Contents, and Committee Pages.

Early fault detection in oil-filled power transformers is an important factor in improving the stability and reliability of the electrical grid. Faults typically result from high-temperature degradation of the mineral oil, either by operation above temperature specification or through localized heating due to electrical discharge and arcing. The standard strategy for diagnosis of fault conditions is to periodically sample the mineral oil and perform dissolved gas analysis (DGA). Varying concentrations of hydrogen (H₂), methane (CH₄), acetylene (C₂H₂), and other hydrocarbons are generated as the oil degrades and can be indicative of fault type. The development of optical fiber-based sensors for dissolved gas detection within transformer oil may provide important new advantages above ex-situ DGA, such as real-time monitoring and spatially resolved (distributed) sensing within the transformer oil. Several different material systems are investigated for detection of acetylene, as well as other hydrocarbons relevant to mineral oil degradation within transformers. Inspired by materials highlighted in the literature for selective acetylene catalysis, several nanostructured nickel / silica oxide-based films are investigated for evanescent field-based sensor materials. In particular, materials are investigated for sensitivity to acetylene, cross-sensitivity to other relevant gas species, and operation at elevated temperature (up to 80°C). Machine learning tools are applied to UV-vis transmission data to enhance gas discrimination and guide sensor design.

Fiber-optic distributed acoustic sensing (DAS) is becoming an increasingly important tool for real-time monitoring of energy and civil infrastructure structural health such as pipelines. We present a systematic theoretical study of the potential for DAS to be directly coupled with guided ultrasonic waves typically used in conventional acoustic non-destructive evaluation (NDE) methods for real-time pipeline health monitoring. We are referring to this innovative new NDE technique as ultrasonic guided wave and optical fiber sensor fusion. In the practical application of DAS coupled with guided ultrasonic waves, the structural design of (1) the specific guided waves excited, (2) the physical installation of the acoustic transducers and the fiber optic sensors, and (3) the functional performance specifications (gauge length, sensitivity, Etc.) of fiber optic DAS have an important influence on overall capabilities of the monitoring system. Meanwhile, physics-based analysis of acoustic waves is still a challenge due to the complex nature of the Lamb wave when it propagates, scatters, and disperses in the presence of structural defects. In this work, we simulate carbon steel pipes relevant for oil and gas pipeline applications with diameters of approximately 6-12” and wall thickness of 0.5” as the objects to be monitored. By establishing and implementing these capabilities, we seek to pursue an in-depth study on structural parameter optimization of DAS network, measurement range, and signal processing with an ultimate goal of increasing the sensitivity and efficacy of DAS to defect identification for various modes of corrosion expected in practice. To study the characteristics of scattered acoustic waves and performance of DAS for defect identification, we simulated the response of DAS for multiple pipe structures, defect types, and DAS sensor network configuration using finite element software Ansys, then the properties of signal response are extracted to construct defect-sensitive features. The raw data simulated, and the associated features extracted can ultimately be utilized as annotated training data to benchmark various designs for DAS applications, guided acoustic excitation sources, and learning model parameters to enhance early detection of potentially problematic defects.

In recent years, optical fiber sensing has emerged as an attractive technology for spatially and temporally distributed monitoring of various types of infrastructure, including pipelines. This technology can provide information such as distributed temperature, corrosion, acoustic, strain, and even vibrations which can be used in real-time monitoring of operational processes or to identify early signatures of impending faults or failures. In this paper, we successfully demonstrate the installation of fiber optic cable inside a pipeline using a long-distance robotic Fiber Optic Deployment Tool (FODT). The FODT is a self-contained semiautonomous robotic device that can propel in a range of pipe diameters to install a fiber optic cable inside the pipeline. It can be controlled remotely, and the current version offers a maximum installation speed of 15 feet/minute. In this demonstration, a distributed fiber cable was installed in a 50’ long, 8.25″ inner diameter steel pipe. The proposed FODT, when combined with distributed sensing, will be an attractive and promising technology for monitoring of oil and gas, water pipelines, and the structural health of pipeline rehabilitation systems.

Fiber optic-based sensing for non-destructive evaluation (NDE) and structural health monitoring of various infrastructure and energy assets is an increasingly important sensing scheme. Because of their immunity to electromagnetic interferences, versatility in sensing mechanisms and designs as well as capability for distributed sensing, the fiber optic sensing is of great interest for embedding within infrastructures using advanced manufacturing methods. However, the protection of fiber optic sensors during advanced manufacturing-based embedding is an important aspect for infrastructure monitoring in practice. While successful installation of fiber optic sensors has been accomplished through application of epoxy or adhesives on infrastructure surfaces, there has been only limited investigation of fiber protection packaging schemes which are compatible with in-situ repair techniques such as the metallic cold-spray. With increasing interest and importance of cold spray-based repair processes, the integration of fiber optic sensors simultaneously during the repair is equally important. In this work, we focus our efforts on investigating various types of packaging schemes for their compatibility and integrability on the surfaces of metallic structures such as oil and gas pipelines during an insitu repair coating. First, we consider sandblasting using silica sand particles of various size for optical fibers on the surface of a metallic coupon as a useful proxy test of sensor packaging stability. Structural damage of packaging is characterized by means of optical microscopy and the optical integrity of embedded fiber optic cables is examined using optical backscatter reflectometry (OBR). In addition, initial investigation of metallic cold-spray embedded fiber optic cables under various packaging on metallic substrates is also considered with early conclusions and future directions.

The paper describes the possibilities of using the detection of fast and slow changes in the state of polarization for the detection of vibrations by an optical single-mode (SM) fiber. The system consists of a polarization beam splitter and a balanced photodetector. This sensing system is cost-effective, which contributes to its use in real operation. On the basis of an experiment with buried fiber near the railroad, the possibility of detecting vibrations with this system was proved. It is possible with simple analyzes to recognize the types of trains and their speed.

The main topic of this paper is the detection state of polarization changes to enhance data security in fiber cable paths. The changes are generated by fiber manipulation or movements, which suggest potential security threats. Our designed system detects these changes using a polarization beam splitter and a pair of photodetectors. The values are subtracted from each other, sampled, and sent for analysis. The software detector applies FFT onto the signal and normalizes the output. The last step compares the sum of the bottom eighth of the spectrum against the threshold.

Laser heated pedestal growth (LHPG) method is a unique technique to grow single crystal fibers and fibrous materials of high temperature ceramics for various photonic and electronic applications. The stability of the solidification process and the floating molten zone created at the interface between the feed and seed materials is critical for ensuring high quality of the fiber including uniformity of diameter. To maintain the molten zone volume constant throughout the dynamic growth process, the typical LHPG system control scheme will modify the relative speed control of fiber-pull rate versus the source material feed rate as constrained by mass conservation. However, due to the dynamic nature of the growth process and the floating state of the molten material, it is prone to instability due to non-uniform heating, heat loss, melt convection, seed-fiber and pedestal material alignments, and other factors which impact growth processes. Sustainable growth process demands a combination of optimized optical components and real-time process controls. Here we present a detailed optical analysis of several candidate LHPG optical designs and compare details of the illumination at the molten zone region during the growth process. In addition, we explore the potential for enhancing the typical process control by utilizing (1) active laser power control and (2) machine vision methods for real-time characterization of the molten zone profile to be integrated into active control schemes. Impacts on the quality of the fiber grown in terms of uniformity in diameters upon active laser power feedback loop to mitigate the molten zone shape variation is also discussed.

In this paper, we demonstrated a fiber acoustic sensor based on a single-mode–multimode–single-mode (SMS) fiber structure. The SMS fiber structure consists of a multimode fiber (MMF) sandwiched between two single-mode fibers (SMFs). Whenever the MMF fiber experiences vibration disturbances, the fiber experiences tensile and compressive strains. By demodulating the vibration-induced intensity fluctuations, the vibrations signals can be quantified. Through employing several SMS sensors in parallel and connecting, and controlling by an optical switch, quasi-distributed sensing can be realized. The proposed sensor system is demonstrated in a laboratory environment and has the capability of detecting a wide range of vibration frequencies from 10 Hz to 400 kHz. In addition, the fiber sensor system is field-tested, where several SMS fiber sensors are mounted on 8.5” diameter steel pipe and excite acoustic emissions based on a magnetostrictive guided wave collar system. The proposed highly sensitive fiber sensor can be potentially used in practical applications of pipeline health condition monitoring.

Nanocomposite thin-film coated fiber optic sensors can be a promising solution to real-time temperature monitoring of electrical assets and imminent failure detection owing to minimal electrical connections and immunity to electromagnetic interference. However, cost of optical interrogation hardware has been a major roadblock for commercialization of fiber optic sensors. Here, we present a novel and simplified design of a fiber optic temperature sensor based on localized surface plasmon resonance (LSPR) response, a low-cost photodiode transimpedance-amplifier (TIA) circuit and collimated LED for monitoring applications where the cost of deployment is a critical consideration. The TIA circuit is designed to capture temperature-induced optical transmission and reflection responses by photocurrent-converted voltage variations communicated through Serial Peripheral Interface (SPI) wireless communication protocols. Wirelessly interrogable optical fiber sensors can therefore be potentially integrated in a wide range of assets such as grid-scale energy storage and medium or high voltage electric power conversion systems. To further minimize system complexity as compared to transmissionbased sensors demonstrated previously, a major emphasis is on a new reflection-based fiber sensor probe. This is also simulated in an optical waveguide physics-based model with Au-incorporated dielectric matrix oxides deposited on the fiber tip. Preliminary results of modeling the temperature response using end-coated reflection fiber probes are discussed.

Results of high-temperature sensing with distributed single-crystal fiber based on a Raman optical-time-domainreflectometry (ROTDR) for nuclear applications is presented. A novel distributed temperature sensing (DTS) system for use with sapphire and YAG fibers was developed to monitor temperature in continuous radiation and high-temperature environments such as nuclear reactor cores or coolant loops. Performance evaluations including accuracy and repeatability of the DTS system are discussed in this paper. Calibration techniques have been implemented to correct the dynamic variation of the optical loss with temperature in the single-crystal fibers. In various sections of different types of fibers and under different temperatures, correction algorithms were used to calculate the calibration parameters to obtain an accurate temperature profile that allows deployment the sensing system under extreme conditions. Continuous calibration and sequential temperature measurement data were analyzed. Distributed temperature measurements with the single-crystal fibers under high radiation loads at high-temperatures have been carried out.

pH is a critical parameter for wellbore integrity and geochemical monitoring in wells for oil and gas production, CO₂ storage, H₂ subsurface storage, and geothermal systems. In situ real-time pH monitoring in subsurface wells is of significant value for wellbore integrity monitoring and predictive analysis of well component deterioration such as casing steel corrosion and cement carbonation. However, harsh environments in subsurface wells have limited many commonly used pH sensors. We have previously demonstrated optical fiber pH sensors coated with metal oxide-based sensing materials such as TiO₂, which offer stability at high pressures and temperatures. In this study, we demonstrated TiO₂ coated optical fibers for real-time distributed pH monitoring based on backscattered light interrogation. TiO₂ coated optical fibers were tested under ambient conditions and wellbore relevant conditions at elevated temperatures. TiO₂ coating was deposited on the optical fibers through a facile sol-gel method. TiO₂ coated optical fibers have shown promising pH sensing results under elevated temperatures and high pH conditions, making them suitable for wellbore cement monitoring.

Spider silks are expected to become biocompatible and bioresorbable optical fibers, which can be utilized to transfer localized optical energy for various biomedical applications such as optical therapy and optical imaging inside living tissue. In this study, the optical properties of eco-friendly native spider silk as an efficient optical fiber have been demonstrated experimentally. The metal shells on the surface of silk fibers are fabricated by using glancing angle deposition technique. Lightwaves with broadband wavelengths are coupled into the silk fibers by direct incorporation of conventional optical fibers. The measurement results show the transmission loss of approximately 2 dB/cm. The optical performances of silk-based core-shell fiber combine with the biocompatibility, bioresorbability, flexibility, and tensile strength. The silk-based core-shell fibers are capable of delivering optical power through biological tissue for biophotonic purposes.