Fiber Bragg Grating Based Sensors and Systems

This book is a collection of papers that originated as a Special Issue, focused on some recent advances related to fiber Bragg grating-based sensors and systems. Conventionally, this book can be divided into three parts: intelligent systems, new types of sensors, and original interrogators. The intelligent systems presented include evaluation of strain transition properties between cast-in FBGs and cast aluminum during uniaxial straining, multi-point strain measurements on a containment vessel, damage detection methods based on long-gauge FBG for highway bridges, evaluation of a coupled sequential approach for rotorcraft landing simulation, wearable hand modules and real-time tracking algorithms for measuring finger joint angles of different hand sizes, and glaze icing detection of 110 kV composite insulators. New types of sensors are reflected in multi-addressed fiber Bragg structures for microwave–photonic sensor systems, its applications in load-sensing wheel hub bearings, and more complex influence in problems of generation of vortex optical beams based on chiral fiber-optic periodic structures. Original interrogators include research in optical designs with curved detectors for FBG interrogation monitors; demonstration of a filterless, multi-point, and temperature-independent FBG dynamical demodulator using pulse-width modulation; and dual wavelength differential detection of FBG sensors with a pulsed DFB laser

Metal coating and embedding fibre optical sensors for industrial applications

This thesis documents the development of two monitoring systems based on metal-coated Fibre Bragg Grating sensors, which are to be validated in two distinct industrial applications within harsh environments. One is intended for the naval sector as part of the NEXT-BEARINGS project, while the other is designed for the energy sector within the framework of the NEWSOL project. The objective of the first application, within the NEXT-BEARINGS (Development of a new generation of naval components for the ship shaft line) project, was to monitor the degradation of antifriction materials in bearings for the naval sector using embedded FBGs with metal coating to measure strain and temperature. The second application, within the framework of the NEWSOL (New StOrage Latent and sensible concept for highly efficient CSP Plants) project, aimed to monitor the performance and operation of novel concrete energy storage components using metallically coated FBGs for Concentrated Solar Power (CSP) plants, which operate at temperatures of up to 550°C. Despite their differences in industrial settings, both applications share similar harsh environments and high temperatures. Therefore, the FOS monitoring solutions developed in this work are all based on metal-coated FBGs as strain and temperature sensors. In this thesis, a metallic coating procedure based on a combination of sputtering and electroplating deposition techniques was developed to apply metallic coatings of Ni and Cu to the FBGs and optical fibres. This procedure allows for the coating of longer lengths of fibre (hundreds of meters) and various thicknesses ranging from a few microns to hundreds of microns. Furthermore, after coating the sensors, a procedure was developed to embed these coated sensors into the antifriction bearing material, which is a tin alloy base, using various techniques such as laser cladding and TIG welding. To verify the research, the metallic coated and embedded FBGs were validated under operational conditions for each use-case. In the case of the NEXT-BEARINGS project, validation was carried out using two distinct test benches adapted to fulfill different technical objectives. On one hand, the response of the embedded FOS within the antifriction material was analysed using a dedicated fatigue machine developed for this purpose. On the other hand, to validate the embedded FOS response for bearing condition monitoring, a test bench designed for testing antifriction bearings in a real vessel was used. During these validations, the metallic-coated embedded FBGs were subjected to pressures up to 250 bar, rotary speeds up to 667 rpm, and temperatures up to 65°C for more than 5500 hours, providing a stable response throughout the tests. In the case of the NEWSOL project, three different validations at laboratory scale, mid-scale, and real scale were conducted. The metallic-coated FBGs were embedded in various thermal storage components made using novel high thermal resistant concretes, and they were tested at temperatures up to 550°C. The embedded FBGs were capable of monitoring the concrete curing process, the operation of the storage components, and the degradation of the concrete. The research concludes by considering future directions for the work in these and other industry sectors

A Critical Review on the Structural Health Monitoring Methods of the Composite Wind Turbine Blades

With increasing turbine size, monitoring of blades becomes increasingly im-portant, in order to prevent catastrophic damages and unnecessary mainte-nance, minimize the downtime and labor cost and improving the safety is-sues and reliability. The present work provides a review and classification of various structural health monitoring (SHM) methods as strain measurement utilizing optical fiber sensors and Fiber Bragg Gratings (FBG’s), active/ pas-sive acoustic emission method, vibration‒based method, thermal imaging method and ultrasonic methods, based on the recent investigations and prom-ising novel techniques. Since accuracy, comprehensiveness and cost-effectiveness are the fundamental parameters in selecting the SHM method, a systematically summarized investigation encompassing methods capabilities/ limitations and sensors types, is needed. Furthermore, the damages which are included in the present work are fiber breakage, matrix cracking, delamina-tion, fiber debonding, crack opening at leading/ trailing edge and ice accre-tion. Taking into account the types of the sensors relevant to different SHM methods, the advantages/ capabilities and disadvantages/ limitations of repre-sented methods are nominated and analyzed

Experimental evaluation of contact stress during cold rolling process with optical fiber Bragg gratings sensors measurements and fast inverse method

International audienceThere is a strategic importance for the steel rolling industry to get a better understanding of the strip–roll interaction to improve roll-gap models, increase strip quality and decrease roll degradation. This requires roll-gap sensors able to measure this interaction under industrial rolling conditions and in real time in order to propose a feed-back control of process parameters. To reach these goals, this paper proposes a new roll-gap friction sensor based on an inverse method that interprets optical fiber Bragg gratings(FBG) strain measurements under the roll surface (fully embedded), which enables to evaluate contact stresses with very short computation times, compatible with real time interpretation. This elastic inverse method is analytical and relies on plane-strain and isothermal assumptions. The experimental apparatus is detailed, technical issues are clearly exposed as well as calibration procedures. Several pilot cold rolling tests have been performed at various rolling speeds and different strip thicknesses in order to demonstrate the industrial feasibility. Resulting evaluations of contact stresses are then compared with numerical simulations. Reasonable agreement is obtained for normal stress (i.e., pressure) but not for shear stress(only an order of magnitude is obtained)

MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology

renewable; green; energy; environment; law; polic

Ultra precision physical micro-machining for integrated optics

This study looks at the application of physical micromachining techniques to integrated optics. These physical micromachining techniques were used to make structures which would be difficult or impossible to produce using conventional cleanroom based technologies.A tuneable Bragg grating was fabricated and characterized and was found to offer an enhanced power efficiency for tuning of 45 pm/mW for the transverse magnetic mode and 39 pm/mW for the transverse electric mode. This an improvement in the operating power efficiency of a factor of 90 over bulk thermally tuned Bragg gratings in silica.A dual cantilever device has also been demonstrated which can operate as a force sensor or variable attenuator. The response of the device to mechanical actuation was measured, and shown to be very well described by conventional fibre optic angular misalignment theory. The device has the potential to be utilized within integrated optical components for sensors or attenuators. An array of devices was fabricated with potential for parallel operation. The fabrication work features the first use of a dicing saw in plunge cutting mode to rapidly produce grooves which were free of chipping.A wire electro discharge unit was designed and built. This was retrofitted to a micromill to give capability to manufacture tools directly on machine. This work built upon previous machining research in the group to allow free form diamond tools to be fabricated. Tools formed by wire electro discharge machining of polycrystalline diamond were formed. A ring tool was created and proved to be able to machine ring structures in the ductile mode regime in germanium oxide glass with a surface roughness of Ra 4.9 nm. This is the first time that ductile mode machining has been achieved in glass with this type of tool. By using a XeF2 etch this was shown to be able to create the structures necessary for whispering gallery mode resonators. A number of exemplar micro disk structures have been researched in this work to test the concept and provide real examples. Firstly a phosphogermanate glass on silica resonator was fabricated. A germanium oxide glass disc was also fabricated using the silicon under-etch process.These trial optical devices have shown that physical machining provides a viable route for fabricating integrated optical elements

Advances in femtosecond micromachining and inscription of micro and nano photonic devices

This thesis has focused on three key areas of interest for femtosecond micromachining and inscription. The first area is micromachining where the work has focused on the ability to process highly repeatable, high precision machining with often extremely complex geometrical structures with little or no damage. High aspect ratio features have been demonstrated in transparent materials, metals and ceramics. Etch depth control was demonstrated especially in the work on phase mask fabrication. Practical chemical sensing and microfluidic devices were also fabricated to demonstrate the capability of the techniques developed during this work. The second area is femtosecond inscription. Here, the work has utilised the non-linear absorption mechanisms associated with femtosecond pulse-material interactions to create highly localised refractive index changes in transparent materials to create complex 3D structures. The techniques employed were then utilised in the fabrication of Phase masks and Optical Coherence Tomography (OCT) phantom calibration artefacts both of which show the potential to fill voids in the development of the fields. This especially the case for the OCT phantoms where there exists no previous artefacts of known shape, allowing for the initial specification of parameters associated with the quality of OCT machines that are being taken up across the world in industry and research. Finally the third area of focus was the combination of all of the techniques developed through work in planar samples to create a range of artefacts in optical fibres. The development of techniques and methods for compensating for the geometrical complexities associated with working with the cylindrical samples with varying refractive indices allowed for fundamental inscription parameters to be examined, structures for use as power monitors and polarisers with the optical fibres and finally the combination of femtosecond inscription and ablation techniques to create a magnetic field sensor with an optical fibre coated in Terfenol-D with directional capability. Through the development of understanding, practical techniques and equipment the work presented here demonstrates several novel pieces of research in the field of femtosecond micromachining and inscription that has provided a broad range of related fields with practical devices that were previously unavailable or that would take great cost and time to facilitate

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs