Aplicações De Métodos De Sensoriamento De Vibração Baseados Em Técnicas

Orientadores: Fabiano Fruett, Claudio FloridiaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Sensores à fibra óptica distribuídos têm sido empregados para monitorar vários parâmetros, tais como temperatura, vibração, tensão mecânica, campo magnético e corrente elétrica. Quando comparados a outras técnicas convencionais, tais sensores são vantajosos devido a suas pequenas dimensões, imunidade a interferências eletromagnéticas, alta adaptabilidade, robustez a ambientes nocivos, dentre outros. Sensores acústicos distribuídos em particular são interessantes devido a sua capacidade em serem usados em aplicações tais como monitoração de saúde de estruturas e vigilância de perímetros. Através da análise em frequência da estrutura, por exemplo uma aeronave, uma ponte, um edifício ou mesmo máquinas em uma fábrica, é possível avaliar sua condição e detectar danos e falhas em um estágio primário. Tais soluções podem cobrir ambas as aplicações de detecção de intrusão e monitoração estrutural com mínimas adaptações no sistema sensor. Desta forma, vibrações e distúrbios pequenas estruturas com resolução de dezenas de centímetros e em grandes estruturas ou perímetros com alguns metros de resolução espacial e centenas de quilômetros de alcance podem ser detectadas. Outra característica útil desta solução baseada em fibra óptica é a possibilidade de ser combinada com técnicas de processamento digital de sinais, permitindo a detecção e localização de perturbações rápidas, reconhecimento de padrões de intrusão em tempo real e multiplexação de dados de superfícies estruturais para aplicações SHM. O principal objetivo desta tese é fazer uso desses recursos para empregar técnicas de DAS como soluções de tecnologias- chave para várias aplicações. Neste trabalho, as técnicas de phase-OTDR foram estudadas e as principais contribuições da tese focaram em trazer soluções inovadoras e validações para aplicações de vigilância e vigilância. Este doutorado teve um período sanduíche nas instalações da RISE Acreo AB, Estocolmo, Suécia, onde experimentos foram realizados e foi parte da 42ª Chamada CISB/Saab/CNPqAbstract: Distributed optical fiber sensors have been increasingly employed for monitoring several parameters, such as temperature, vibration, strain, magnetic field and current. When compared to other conventional techniques, these sensors are advantageous due to their small dimensions, lightweight, immunity to electromagnetic interference, high adaptability, robustness to hazardous environments, less complex data multiplexing, the feasibility to be embedded into structures with minimum invasion, the capability to extract data with high resolution from long perimeters using a single optical fiber and detect multiple events along the fiber. In particular, distributed acoustic sensors (DAS) based on optical time domain reflectometry (OTDR), are of high interest, due to their capability to be used in applications such as structural health monitoring (SHM) and perimeter surveillance. Through the frequency analysis of a structure, for instance an aircraft, a bridge, a building or even machines in a workshop, it is possible to evaluate its condition and detect damages and failures at an early stage. Also, OTDR based solutions for vibration monitoring can be easily adapted with minimum setup modifications to detect intrusion in a perimeter, a useful tool for surveillance of military facilities, laboratories, power plants and homeland security. The same OTDR technique can be used as a non-destructive diagnostic tool to evaluate vibrations and disturbances on both small structures with some dozens of centimeters¿ resolution and in big structures or perimeters with some meters of spatial resolution and hundreds of kilometers of reach. Another useful feature of this optical fiber based solution is the possibility to be combined with high-performance digital signal processing techniques, enabling fast disturbance detection and location, real-time intrusion pattern recognition and fast data multiplexing of structure surfaces for SHM applications. The main goal of this thesis is to make use of these features to employ DAS techniques as key enabling technologies solutions for several applications. In this work, OTDR based techniques were studied and the thesis main contributions were focused on bringing innovative solutions and validations for SHM and surveillance applications. This PhD had a sandwich period at Acreo AB, Stockholm, Sweden, where experimental tests were performed and it was part of the 42ª CISB/Saab/CNPq CalDoutoradoEletrônica, Microeletrônica e OptoeletrônicaDoutora em Engenharia Elétrica202816/2015-0CAPESCNP

Distributed Fiber Ultrasonic Sensor and Pattern Recognition Analytics

Ultrasound interrogation and structural health monitoring technologies have found a wide array of applications in the health care, aerospace, automobile, and energy sectors. To achieve high spatial resolution, large array electrical transducers have been used in these applications to harness sufficient data for both monitoring and diagnoses. Electronic-based sensors have been the standard technology for ultrasonic detection, which are often expensive and cumbersome for use in large scale deployments. Fiber optical sensors have advantageous characteristics of smaller cross-sectional area, humidity-resistance, immunity to electromagnetic interference, as well as compatibility with telemetry and telecommunications applications, which make them attractive alternatives for use as ultrasonic sensors. A unique trait of fiber sensors is its ability to perform distributed acoustic measurements to achieve high spatial resolution detection using a single fiber. Using ultrafast laser direct-writing techniques, nano-reflectors can be induced inside fiber cores to drastically improve the signal-to-noise ratio of distributed fiber sensors. This dissertation explores the applications of laser-fabricated nano-reflectors in optical fiber cores for both multi-point intrinsic Fabry–Perot (FP) interferometer sensors and a distributed phase-sensitive optical time-domain reflectometry (φ-OTDR) to be used in ultrasound detection. Multi-point intrinsic FP interferometer was based on swept-frequency interferometry with optoelectronic phase-locked loop that interrogated cascaded FP cavities to obtain ultrasound patterns. The ultrasound was demodulated through reassigned short time Fourier transform incorporating with maximum-energy ridges tracking. With tens of centimeters cavity length, this approach achieved 20kHz ultrasound detection that was finesse-insensitive, noise-free, high-sensitivity and multiplex-scalability. The use of φ-OTDR with enhanced Rayleigh backscattering compensated the deficiencies of low inherent signal-to-noise ratio (SNR). The dynamic strain between two adjacent nano-reflectors was extracted by using 3×3 coupler demodulation within Michelson interferometer. With an improvement of over 35 dB SNR, this was adequate for the recognition of the subtle differences in signals, such as footstep of human locomotion and abnormal acoustic echoes from pipeline corrosion. With the help of artificial intelligence in pattern recognition, high accuracy of events’ identification can be achieved in perimeter security and structural health monitoring, with further potential that can be harnessed using unsurprised learning

Optical fiber sensors in physical intrusion detection systems: A review

Fiber optic sensors have become a mainstream sensing technology within a large array of applications due to their inherent benefits. They are now used significantly in structural health monitoring, and are an essential solution for monitoring harsh environments. Since their first development over 30 years ago, they have also found promise in security applications. This paper reviews all of the optical fiber-based techniques used in physical intrusion detection systems. It details the different approaches used for sensing, interrogation, and networking, by research groups, attempting to secure both commercial and residential premises from physical security breaches. The advantages and the disadvantages of the systems are discussed, and each of the different perimeter protection methods is outlined, namely, in-ground, perimeter fence, and window and door protection. This paper reviews the progress in optical fiber-based intrusion detection techniques from the past through to the current state-of-the-art systems and identifies areas, which may provide opportunities for improvement, as well as proposing future directions in this field

Time-expanded phase-sensitive optical time-domain reflectometry

Phase-sensitive optical time-domain reflectometry (ΦOTDR) is a well-established technique that provides spatio-temporal measurements of an environmental variable in real time. This unique capability is being leveraged in an ever-increasing number of applications, from energy transportation or civil security to seismology. To date, a wide number of different approaches have been implemented, providing a plethora of options in terms of performance (resolution, acquisition bandwidth, sensitivity or range). However, to achieve high spatial resolutions, detection bandwidths in the GHz range are typically required, substantially increasing the system cost and complexity. Here, we present a novel ΦOTDR approach that allows a customized time expansion of the received optical traces. Hence, the presented technique reaches cm-scale spatial resolutions over 1 km while requiring a remarkably low detection bandwidth in the MHz regime. This approach relies on the use of dual-comb spectrometry to interrogate the fibre and sample the backscattered light. Random phase-spectral coding is applied to the employed combs to maximize the signal-to-noise ratio of the sensing scheme. A comparison of the proposed method with alternative approaches aimed at similar operation features is provided, along with a thorough analysis of the new trade-offs. Our results demonstrate a radically novel high-resolution ΦOTDR scheme, which could promote new applications in metrology, borehole monitoring or aerospace

Adaptable Pulse Compression in φ-OTDR With Direct Digital Synthesis of Probe Waveforms and Rigorously Defined Nonlinear Chirping

Recent research in Phase-Sensitive Optical Time Doman Reflectometry (φ-OTDR) has been focused, among others, on performing spatially resolved measurements with various methods including the use of frequency modulated probes. However, conventional schemes either rely on phase-coded sequences, involve inflexible generation of the probe frequency modulation or mostly employ simple linear frequency modulated (LFM) pulses which suffer from elevated sidelobes introducing degradation in range resolution. In this contribution, we propose and experimentally demonstrate a novel φ-OTDR scheme which employs a readily adaptable Direct Digital Synthesis (DDS) of pulses with custom frequency modulation formats and demonstrate advanced optical pulse compression with a nonlinear frequency modulated (NLFM) waveform containing a complex, rigorously defined modulation law optimized for bandwidth-limited synthesis and sidelobe suppression. The proposed method offers high fidelity chirped waveforms, and when employed in resolving a 50-cm event at ∼1.13 km using a 1.2-μs probe pulse, matched filtering with the DDS-generated NLFM waveform results in a significant reduction in range ambiguity owing to autocorrelation sidelobe suppression of ∼20 dB with no averages and windowing functions, for an improvement of ∼16 dB compared to conventional linear chirping. Experimental results also show that the contribution of autocorrelation sidelobes to the power in the compressed backscattering responses around localized events is suppressed by up to ∼18 dB when advanced pulse compression with an optical NLFM pulse is employed

Intensity based interrogation of optical fibre sensors for industrial automation and intrusion detection systems

In this study, the use of optical fibre sensors for intrusion detection and industrial automation systems has been demonstrated, with a particular focus on low cost, intensity-based, interrogation techniques. The use of optical fibre sensors for intrusion detection systems to secure residential, commercial, and industrial premises against potential security breaches has been extensively reviewed in this thesis. Fibre Bragg grating (FBG) sensing is one form of optical fibre sensing that has been underutilised in applications such as in-ground, in-fence, and window and door monitoring, and addressing that opportunity has been a major goal of this thesis. Both security and industrial sensor systems must include some centralised intelligence (electronic controller) and ideally both automation and security sensor systems would be controlled and monitored by the same centralised system. Optical fibre sensor systems that could be used for either application have been designed, developed, and tested in this study, and optoelectronic interfaces for integrating these sensors with electronic controllers have been demonstrated. The versatility of FBG sensors means that they are also ideal for certain mainstream industrial applications. Two novel transducers have been developed in this work; a highly sensitive low pressure FBG diaphragm transducer and a FBG load cell transducer. Both have been designed to allow interrogation of the optical signal could occur within the housing of the individual sensors themselves. This is achieved in a simple and low cost manner that enables the output of the transducers to be easily connected to standard electronic controllers, such as programmable logic controllers. Furthermore, some of the nonlinear characteristics of FBG sensors have been explored with the aim of developing transducers that are inherently decoupled from strain and temperature interference. One of the major advantages of optical fibre sensors is their ability to be both time division and wavelength division multiplexed. The intensity-based interrogation techniques used here complement this attribute and are a major consideration when developing the transducers and optoelectronic circuits. A time division multiplexing technique, using transmit-reflect detection and incorporating a dual bus, has also been developed. This system architecture enables all the different optical fibre transducers on the network to have the same Bragg wavelength and hence the number of spare replacement transducers required is minimal. Moreover, sensors can be replaced in an online control system without disrupting the network. In addition, by analysing both the transmitted and reflected signals, problems associated with optical power fluctuations are eliminated and the intensity of the sensor signals is increased through differential amplification. Overall, the research addresses the limitations of conventional electrical sensors, such as susceptibility to corrosive damage in wet and corrosive environments, and risk of causing an explosion in hazardous environments, as well as the limitations of current stand-alone optical fibre sensor systems. This thesis supports more alert, reliable, affordable, and coordinated, control and monitoring systems in an on-line environment

Chirped-pulse phase-sensitive optical time domain reflectometry

El mundo actual funciona gracias a las grandes infraestructuras que dotan de energía y transporte seguros a sus ciudadanos. Dichas infraestructuras (presas, diques, gaseoductos, oleoductos, puentes, líneas de ferrocarril, carreteras…) típicamente presentan grandes dimensiones y es especialmente difícil monitorizar su buen funcionamiento y su salud estructural además de protegerlas de posibles amenazas. Los sensores distribuidos de fibra óptica son una solución fiable y rentable para esta problemática, ya que permiten medir vibraciones, deformaciones y temperatura a lo largo de todos los puntos de una fibra óptica estándar de comunicaciones. Los sensores de fibra óptica basados en scattering Rayleigh son particularmente útiles cuando las medidas deben ser realizadas en tiempo real, como por ejemplo en la detección y caracterización de vibraciones. En esta tesis, se ha realizado un estudio acerca de distintas soluciones y alternativas a las limitaciones de la tecnología OTDR. Se ha propuesto una nueva técnica, derivada de ésta, que ofrece unas prestaciones que superan notablemente a las de los sistemas OTDR tradicionales. Para ello, en primer lugar, se ha procedido a realizar un estudio en profundidad de los fundamentos y el estado del arte de las técnicas de monitorización basadas en Reflectometría Óptica en el Dominio del Tiempo (OTDR, por sus siglas en inglés) y, en particular, sobre la implementación sensible a la fase, también conocida como OTDR. Se ha estudiado la limitación en rango y resolución de los sistemas OTDR principalmente asociada a la aparición de efectos no lineales como la inestabilidad de modulación. Actualmente, un OTDR tradicional presenta una resolución máxima del orden de los 10 metros para un rango de medida del orden de pocas decenas de km (si no se aplica ningún tipo de técnica de amplificación distribuida). Además de estudiar esta limitación y a qué es debida, se han propuesto dos técnicas para mitigar los efectos perjudiciales de la MI. En primer lugar, se ha realizado un estudio del efecto de la forma de los pulsos ópticos empleados en el sensor en la traza retrodispersada en un OTDR. Se ha podido comprobar cómo los pulsos triangulares o gaussianos presentan mayor robustez que los pulsos rectangulares, tradicionalmente empleados, frente a la MI. En segundo lugar, se ha propuesto una técnica basada en el concepto de Amplificación de Pulsos Chirpeados (CPA, por sus siglas en inglés), que ha permitido desarrollar un OTDR con resoluciones milimétricas. Hasta el momento ningún OTDR había podido llegar a tales resoluciones, lo que abre un nuevo abanico de aplicaciones a la tecnología OTDR donde se requiera alta resolución espacial en la medida. También se ha estudiado la otra gran limitación de este tipo de sensores: su comportamiento no lineal ante una perturbación. Actualmente, salvo que se implementen técnicas de recuperación de fase o barridos en longitud de onda que implican más complejidad, coste y tiempo de medida, no es posible realizar medidas cuantificables de temperatura o deformaciones. Del mismo modo, tampoco se pueden realizar medidas acústicas reales. En este trabajo, en primer lugar, se propone emplear la técnica de Reconstrucción de Fase empleando Diferenciación Óptica Ultrarápida (PROUD, por sus siglas en inglés) para recuperar el campo complejo de una señal OTDR. Con esta medida, el sensor pasaría a comportarse de forma lineal sin la complejidad intrínseca de los métodos tradicionales de detección de fase. En segundo lugar, y de aquí viene el nombre de esta tesis doctoral, se propone el uso de pulsos chirpeados en los sensores OTDR. La nueva técnica llamada Chirped-Pulse OTDR, ha permitido la medida de forma lineal de cambios de temperatura y deformaciones, en un único disparo y sin la necesidad de realizar barridos en frecuencia o implementar detección coherente. A lo largo de este trabajo, se han alcanzado resoluciones de 0.5mK/4n y se ha demostrado la posibilidad de hacer medidas acústicas reales. También se han estudiado las limitaciones de esta técnica y propuesto varias soluciones. Se ha demostrado que el ruido de fase del láser empleado en el sistema, puede ser mitigado con esta nueva técnica. Además, se ha propuesto el uso de amplificación distribuida basada en scattering Raman estimulado para alcanzar rangos de medida mayores, hasta 75 km con una resolución espacial de 10 m

Permanently-Installed Distributed Pressure Sensors for Downhole Applications

Technology advancements (e.g., hydraulic fracturing and horizontal drilling) to recover unconventional oil and gas (UOG) resources are critical in maintaining future U.S. oil and gas production levels. Permanently installed distributed downhole pressure sensors could monitor fracture propagation, assess the effectiveness of hydraulic fracturing, and optimize hydraulic fracturing placement so that overall UOG recovery efficiency can be increased. However, the harsh environment (high temperatures, high pressures, strong vibration, and presence of brine, mud, debris, hydrate, and various gases), the long data telemetry distance, and the requirements of reliability and service lifetime make the downhole monitoring a very challenging task. To combat these challenges, this thesis presents three sensing systems for downhole pressure monitoring. First, A microwave-photonic low-coherence interferometry (MPLCI) system is proposed for optical fiber based distributed sensing. The system can be used to interrogate the intrinsic Fabry–Pérot interferometers (IFPIs) based distributed downhole pressure sensors. Assisted by an unbalanced Michelson interferometer (MI), a low-coherence laser source is used to interrogate IFPIs along with an optical fiber for a dark zone-free (or spatially continuous) distributed measurement. By combining the advantages of microwaves and photonics, the MPLCI system can synergistically achieve high sensitivity and high spatial resolution. Second, to solve the packaging and drift problems in optical fiber sensors, an all-digital sensing method based on an electrical encoder is developed for downhole pressure monitoring. The key innovation of the all-digital sensor concept is the built-in nonelectric analog-to-digital converter (ADC), which eliminates the need for downhole electronics for signal conditioning and telemetry in conventional electrical downhole sensors. As such, the sensors are more robust, less expensive, and have less drift in comparison with the existing sensors. Because the sensor outputs are digital in nature, the developed sensors can be remotely logged over a long distance, and many sensors can be digitally multiplexed for distributed sensing using a single surface instrument. The all-digital pressure sensors and their surface instrument were designed, engineered, fabricated, and calibrated. The integrated sensing system was tested/validated at both laboratory and research wellbores. Third, to solve the hysteresis problem induced by the electrical encoder, a non-contact optical encoder based all-digital pressure sensor for downhole applications is proposed. The proposed sensor combines the advantages of both optical fiber and all-digital sensing method. The noncontact-type encoder, which is composed of an encoding pad and an all-glass optical fiber sensing head. A glass additive and subtractive manufacturing (ASM) system was used to embed the multi-channel optical fibers into a bulk-fused silica glass substrate with high positioning accuracy and good thermal stability even at elevated temperatures. The optical fiber only serves as the telemetry channel to directly transmit the data in digital format, such that the system has long-distance telemetry capability as well as low drift. The proposed pressure sensor was manufactured and experimentally verified to have a high SNR, linear pressure response, and good long-term stability. In addition, a mathematical model to study the relationships between the sensor’s performances and design parameters was established

Fiber Optic Sensors in Chemical and Biological Applications

The Special Issue "Fiber Optic Sensors in Chemical and Biological Applications” gathers recent original papers. The subjects of the papers cover a broad range of optical fiber chemical sensors and biosensors applied for regulation in bioreactors, to novel concepts of intrinsic optical fiber sensors