Fiber optic sensors offer the ability to measure different types of physical quantities in more harsh environments, such as temperature, pressure and deformations. Some of these demanding environments include chemicals that affect the sensitivity of the sensor, and therefore its resili-ence deteriorates. This work focuses on using experimental techniques to find a method that protects the optical fiber in these chemically demand-ing environments, by coating the fiber with a polymer layer which has the task of protecting it in such environments. A challenge that comes with coating the fiber optic sensor with a polymer layer is that the ability to obtain information becomes more difficult as, its sensitivity deterio-rates. In this project, a type of polymer called polyimide will be tested, using different concentrations and number of layers coated on the optical sensor to investigate the extent that these factors affect the sensor´s ability to cope in chemically demanding environments and also how the sensi-tivity is affected. Thus, the coating method used was soap film coating (SFC). A spectrometer was used to examine the sensitivity of the sensor (using total internal reflection (TIR) and surface plasmon resonance (SPR)). The examination of the resistance of the optical fiber was meas-ured by immersing the polymer-coated sensor in a corrosive liquid for various time intervals and then examining its protective ability. The re-sults obtained through this work demonstrate that polyimide as a coating material provides a protective effect by improving the resistance. The sen-sitivity was most affected when the concentration of the polyimide layer increased from 1-layer to 2-layer polyimide at high concentrations. Re-sistance also increased as the concentration increased, however, 1-layer and 2-layer protection did not have a major impact. The results of this project can be used to further test different types of polymers, for example PVDF. Even more tests with the same attitude and conditions should be carried out to ensure the conclusions and results, and to estimate the measurement uncertainties in the work.

No description available.

Force and moment balances have proved to be essential in the measurement and calculation of aerodynamic properties during wind tunnel testing. With the recent advancements of technology, new fiber optic sensors have been designed to replace the conventional foil strain gage sensors commonly found on balances, thereby offering several distinct advantages. The use of fiber optic sensors on a balance brings with it some potential advantages over conventional strain gage balances including increased resolution and accuracy, insensitivity to electromagnetic interference, and the capability of use at high temperatures. By using the fiber optic sensors, some of the limitations of the conventional balance can be overcome, leading to a better overall balance design. This thesis considers an initial trial application of new fiber optic sensors on a conventional, six-component sting balance while retaining the original foil strain gage sensors for comparison. Tests were conducted with a blunt, 10º half-angle cone model in the Virginia Tech 9x9 inch Supersonic Wind Tunnel at Mach 2.4 with a total pressure of 48 psia and ambient total temperature of 25.3ºC. Results showed a close comparison between the foil strain gages and the fiber optic sensor measurements, which were set up to measure the normal force and pitching moment on the blunt cone model. A Finite Element Model (FEM) of the sting balance was produced in order to determine the best locations for the fiber optic sensors on the sting balance. Computational Fluid Dynamics (CFD) was also used in order to predict and compare the results acquired from all of the sensors. / Master of Science

Distributed temperature and strain sensing is demanded for a wide range of applications including real-time monitoring of industrial processes, health monitoring of civil infrastructures, etc. Optical fiber distributed sensors have attracted tremendous research interests in the past decade to meet the requirements of such applications. This research presents a multiplexed sensor array for distributed temperature and strain sensing that can multiplex a large number of UV-induced sensors along a single fiber. The objective of this research is to develop a quasi-distributed sensing technology that will greatly increase the multiplexing capacity of a sensor network and can measure temperature and strain with a high accuracy and high resolution. UV-induced intrinsic Fabry-Perot interferometric (IFPI) optical fiber sensors, which have low reflectance and low power loss, are good candidates for multiplexed sensors networks. Partial reflectors are constructed by irradiating photosensitive fiber with a UV laser beam. A pair of reflectors will form a Fabry-Perot interferometer that can be used for temperature and strain sensing. A sensor fabrication system based on a pulsed excimer laser and a shadow mask is developed. A spectrum-based measurement system is presented to measure the interference fringes of IFPI sensors. A swept coherent light source is used as the light source. The spectral responses of the IFPI sensors at different wavelengths are measured. A frequency division multiplexing (FDM) scheme is proposed. Multiple sensors with different optical path differences (OPD) have different sub-carrier frequencies in the measured spectrum of the IFPI sensors. The multiplexing capacity of the sensor system and the crosstalk between sensors are analyzed. Frequency estimation based digital signal processing algorithms are developed to determine the absolute OPDs of the IFPI sensors. Digital filters are used to select individual frequency components and filter out the noise. The frequency and phase of the filtered signal are estimated by means of peak finding and phase linear regression methods. The performance of the signal processing algorithms is analyzed. Experimental results for temperature and strain measurement are demonstrated. The discrimination of the temperature and strain cross sensitivity is investigated. Experimental results show that UV-induced IFPI sensors in a FDM scheme have good measurement accuracy for temperature and strain sensing and potentially have a large multiplexing capacity. / Ph. D.

A novel fiber optic structure, termed stochastic ordered hole fibers, has been developed that contains an ordered array of six hollow tubes surrounding a hollow core, combined with a nanoporous glass creating a unique fully three dimensional pore/fiber configuration. The objective of this study is to increase the functionality of these stochastic ordered hole fibers, as well as porous clad fibers, by integrating electronic device components such as conductors, and semiconductors, and optically active materials on and in the optical fiber pore structures. Conductive copper pathways were created on/in the solid core fibers using an electroless deposition technique. A chemical vapor deposition system was built in order to attempt the deposition of silicon in on the porous clad fibers. Additionally, conductive poly(3,4-ethylenedioxythiophene)- poly(styrene sulfonate) (PEDOT:PSS) and photoactive polymer blend poly(3- hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-)6,6)C61 (P3HT: PCBM) were deposited on the fibers using dip coating techniques. Quantum dots of Cadmium Selenide (CdSe) with particle sizes of ranging from 2- 10 nm were deposited in the stochastic ordered hole fibers. SEM and EDS analysis confirm that copper, polymer materials, and quantum dots were deposited in the pore structure and on the surface of the fibers. Finally, resistance measurements indicate that the electrolessly deposited copper coatings have sufficient conductivity to be used as metallic contacts or resistive heating elements. / Master of Science

The electrostatic self-assembly (ESA) method presents an effective application in the field of biosensing due to the uniform nanoscale structure. In previous research, a single mode fiber (SMF) sensor system had been investigated for the thin-film measurement due to the high fringe visibility. However, compared with a SMF sensor system, a multimode fiber (MMF) sensor system is lower-cost and has larger sensing area (the fiber core), providing the potential for higher sensing efficiency. In this thesis, a multimode fiber-optic sensor has been developed based on extrinsic Fabry-Perot interferometry (EFPI) for the measurement of optical thickness in self-assembled thin film layers as well as for the immunosensing test. The sensor was fabricated by connecting a multimode fiber (MMF) and a silica wafer. A Fabry-Perot cavity was formed by the reflections from the two interfaces of the wafer. The negatively charged silica wafer could be used as the substrate for the thin film immobilization scheme. The sensor is incorporated into the white-light interferometric system. By monitoring the optical cavity length increment, the self-assembled thin film thickness was measured; the immunoreaction between immunoglobulin G (IgG) and anti-IgG was investigated. / Master of Science

Elevators are a necessary component of the modern urban and suburban life. The guide rails the car and counterweight move on are the most sensitive parts when it comes to de-habilitating damage that can be caused by an earthquake. Conventional sensors are becoming obsolete in sensing for today's multistory buildings because they don't monitor the structural health of the guide rails. This sensing task falls into the fiber sensing niche market because of a fiber sensor's ability to be multiplexed. Previous work by Taplin and Jackson showed demodulation of the interference spectrum of two Fabry-Perot cavities using Fourier analysis. The goal of this research is to use Fourier analysis to demodulate the spectrum of four multiplexed extrinsic Fabry-Perot fiber interferometers for strain measurements. Comparisons of fiber, foil, and theoretical strains are made. Also, experiments showing the system's air-gap stability and crosstalk are provided. / Master of Science

The development and transition of optical fiber sensors from experimental stage to practical applications largely depends on manufacturing cost and simplicity. To date, in-fiber grating sensors are largely manufactured by ultraviolet lasers despite higher fabrication cost and complexity. Besides, ultraviolet radiation can only write gratings in doped fibers. Therefore, reaping the benefits of existing fibers such as pure silica fiber, photonics crystal fibers etc. cannot be achieved using this technique. In contrast, uses of ultra-fast lasers have the potential to eliminate or minimize those drawbacks. However, extensive fabrication and packaging research is required for ultrafast laser technology to mature and offer grating based sensors fabrication in industrial scale. This dissertation presents design and fabrication of fiber optic sensors using femtosecond laser for measurement of ambient refractive index and temperature. The femtosecond laser operating at 780 nm with pulse duration of 172 fs and pulse repetition rate of 1 kHz is used to study bulk index modification and fabricate fiber long period and short period gratings. Effective and reliable fabrication of in-fiber gratings requires spatial control of refractive index written in optical fiber. With an aim to better control spatial index modulation in direct ultrafast writing, primary focus of this work is given to write single-shot submicron periodic voids in bulk glass. Femtosecond pulse filamentation in glass is studied to understand the morphology of bulk index change written by ultrashort pulses. Laser writing parameters (such as beam diameter, pulse energy, scanning speed, depth of focus, etc.) are then further tuned to write pulse filamentation induced refractive index change in optical fibers suitable for fiber grating fabrication. In order to design and tailor grating’s spectrum, measurement of in-fiber index is introduced in this work. We propose fiber Bragg grating based Fabry-Perot cavity structure (cavity length, L= 10 mm) to characterize femtosecond pulse filamentation induced refractive index change in the core of standard SMF. In addition, Mach-Zehnder interferometer (MZI) is proposed as an alternative yet effective and low cost tool to measure in-fiber index change. Comsol simulation is used to validate the quantification of index change. Measured index change is used in Optiwave simulation to design fiber long period gratings in standard telecommunication and pure silica core fibers. To increase fabrication reliability, we introduce inscription of helical long period gratings using a custom made rotary stage. Tapered photonic crystal and microfiber based Mach-Zehnder interferometer is also investigated for ambient refractive index measurement. Miniature fiber Bragg grating written in microfiber Mach-Zehnder interferometer is used in this work for multi-parameter sensing as well as temperature compensated refractive index sensing. Microfiber Bragg gratings buried in materials of higher thermal expansion coefficient is also proposed to significantly enhance temperature sensitivity. / Graduate / 0548, 0794, 0775 / fariduvic@gmail.com

<p>U postupku praćenja stanja građevinskih struktura vr&scaron;i se nadzor nad fizičkim (mehaničkim), meteorolo&scaron;kim i hemijskim parametrima. U praksi se za merenje navedenih parametara koristi veliki broj instrumenata-senzora. Na osnovu uvida u aktuelno stanje iz oblasti istraživanja, zatim evidentne potrebe za istraživanjima o potencijalu postojećih i novih instrumenata i senzora za merenje geometrijskih deformacija i ekspanziji kori&scaron;ćenja fiber optičke senzorske tehnologije definisana je oblast istraživanja ove doktorske disertacije. U doktorskoj disertaciji izvr&scaron;eno je teorijsko i eksperimentalno istraživanje postojećih metoda za praćenje geometrijskih deformacija i razvoj sistema baziranog na fiber optičkom senzoru zakrivljenosti (eng. Fiber Optic Curvature Sensor &ndash; FOCS).</p> / <p>In the process of structural health monitoring (SHM) inspection of physical (mechanical), meteorological and chemical parameters is performed. In practice, a large number of instruments-sensors are used to measure these parameters. The field of research of this doctoral dissertation is based on the insight into the current state in the field of research, then the evident need for research on the potential of existing and new instruments and sensors for measuring geometric deformations and the usage expansion of fiber optic sensor technology. In the doctoral dissertation, theoretical and experimental study of the existing methods for monitoring geometric deformations and the development of a fiber optic curvature sensor (FOCS) system is performed.</p>

This thesis deals with asset management of structures through Building Information Modelling (BIM) and Digital Twins. Background: Current inspection and management processes for civil structures are time-consuming and can even be inaccurate. There is an increasingly high potential to improve these processes through recent advances in technology. Digital Twins offer a common platform to these technologies, so they can interact and be used to their optimal performance. Other industries have significantly advanced in the development of Digital Twins, however, in the construction industry there are still many gaps and room for improvement. Aim and objectives: The main aim of this project was to investigate the status of Digital Twins in the construction industry and propose a methodology for a Digital Twin for asset management of structures. The three immediate objectives sought are (i) Perform a literature review to establish the current practice with digital twins, in both construction and other industries, and what are the gaps for asset management of structures; (ii) Participate in a pilot experimental program that yields data to a potential digital twin prototype; and (iii) Define a methodology for a digital twin for asset management of structures which fills the identified gaps. Methods of investigation: A literature review was performed and served as basis for the development of a methodology for a digital twin. A pilot experimental program was defined and performed, and its results were used for BIM and Finite Element (FE) models. A webapp was also created using Autodesk Forge and Java programming language, andthe BIM model was uploaded into it. Results: The literature review provided insight into the maturity level of digital twins, as well as on bridge inspection, maintenance and monitoring, BIM, facility and asset management, and Bridge Management Systems (BMS). A methodology to achieve a digital twin for asset management was proposed, and the conducted experimental program yielded data results to be used in future research. Conclusion: There has been significant progress in technology to improve structural assessment and analysis, however, their full potential is still under-explored. A digital twin created in a common data environment can provide a platform for these technologies to improve efficiency of current practices. Nonetheless, the construction industry is still significantly behind other industries such as aerospace and automotive.