Fibre Bragg gratings in polymer optical fibre for applications in sensing

This thesis presents the potential sensing applications of fibre Bragg gratings in polymer optical fibres. Fibre Bragg gratings are fabricated in different kinds of polymer optical fibres, including Poly methyl methacrylate (PMMA) and TOPAS cyclic olefin copolymer based microstructured polymer optical fibres and PMMA based step-index photosensitive polymer optical fibre, using the 325nm continuous wave ultraviolet laser and phase mask technique. The thermal response of fabricated microstructured polymer optical fibre Bragg gratings has been characterized. The PMMA based single mode microstructured polymer optical fibre Bragg gratings exhibit negative non-linear Bragg wavelength shift with temperature, including a quasi-linear region. The thermal sensitivity of such Bragg gratings in the linear region is up to -97pm/°C. A permanent shift in the grating wavelength at room temperature is observed when such gratings are heated above a threshold temperature which can be extended by annealing the fibre before grating inscription. The largest positive Bragg wavelength shift with temperature in transmission is observed in TOPAS based few moded microstructured polymer optical fibre Bragg gratings and the measured temperature sensitivity is 250±0.5pm/°C. Gluing method is developed to maintain stable optical coupling between PMMA based single mode step index polymer optical fibre Bragg gratings and single mode step index silica optical fibre. Being benefit from this success, polymer optical fibre Bragg gratings are able to be characterised for their temperature, humidity and strain sensitivity, which are -48.2±1pm/°C, 38.3±0.5pm per %RH and 1.33±0.04 pm/µ??respectively. These sensitivities have been utilised to achieve several applications. The strain sensitivity of step index polymer optical fibre Bragg grating devices has been exploited in the potential application of the strain condition monitoring of heavy textiles and when being attached to textile specimens with certain type of adhesives. These polymer fibre Bragg grating devices show better strain transfer and lower structure reinforcement than silica optical fibre Bragg grating devices. The humidity sensitivity of step index polymer optical fibre Bragg grating devices is applied to detecting water in jet fuel and is proved to be able to measure water content of less than 20 ppm in Jet fuel. A simultaneous temperature and humidity sensor is also made by attaching a polymer fibre Bragg grating to a silica optical fibre Bragg grating and it shows better humidity measurement accuracy than that of electronic competitors.

Humidity insensitive TOPAS polymer fiber Bragg grating sensor

We report the first experimental demonstration of a humidity insensitive polymer optical fiber Bragg grating (FBG), as well as the first FBG recorded in a TOPAS polymer optical fiber in the important low loss 850nm spectral region. For the demonstration we have fabricated FBGs with resonance wavelength around 850 nm and 1550 nm in single-mode microstructured polymer optical fibers made of TOPAS and the conventional poly (methyl methacrylate) (PMMA). Characterization of the FBGs shows that the TOPAS FBG is more than 50 times less sensitive to humidity than the conventional PMMA FBG in both wavelength regimes. This makes the TOPAS FBG very appealing for sensing applications as it appears to solve the humidity sensitivity problem suffered by the PMMA FBG. © 2011 Optical Society of America.

Humidity insensitive TOPAS polymer fiber Bragg grating sensor

We report the first experimental demonstration of a humidity insensitive polymer optical fiber Bragg grating (FBG), as well as the first FBG recorded in a TOPAS polymer optical fiber in the important low loss 850nm spectral region. For the demonstration we have fabricated FBGs with resonance wavelength around 850 nm and 1550 nm in single-mode microstructured polymer optical fibers made of TOPAS and the conventional poly (methyl methacrylate) (PMMA). Characterization of the FBGs shows that the TOPAS FBG is more than 50 times less sensitive to humidity than the conventional PMMA FBG in both wavelength regimes. This makes the TOPAS FBG very appealing for sensing applications as it appears to solve the humidity sensitivity problem suffered by the PMMA FBG. © 2011 Optical Society of America.

Polymer fibre Bragg gratings and sensing

Polymer FBGs have advantages for sensing because of low Young's modulus, high temperature sensitivity, large strain range and so on. They are attractive for many niche applications such as structural health monitoring of composite materials, biochemical and biomedical sensing. While polymer FBGs have been developed for some time, polymer microfibre Bragg gratings are developed only recently and have shown to introduce some interesting features, e.g. increased pressure sensitivity to pressure / force and improved response time to humidity. We will report and discuss the recent work on polymer FBG and polymer microfibre Bragg gratings as well as their applications such as accelerometer, humidity sensor and force and pressure sensor. © 2015 OSA.

Molecular alignment relaxation in polymer optical fibers for sensing applications

A systematic study of annealing behavior of drawn PMMA fibers was performed. Annealing dynamics were investigated under different environmental conditions by fiber longitudinal shrinkage monitoring. The shrinkage process was found to follow a stretched exponential decay function revealing the heterogeneous nature of the underlying molecular dynamics. The complex dependence of the fiber shrinkage on initial degree of molecular alignment in the fiber, annealing time and temperature was investigated and interpreted. Moreover, humidity was shown to have a profound effect on the annealing process, which was not recognized previously. Annealing was also shown to have considerable effect on the fiber mechanical properties associated with the relaxation of molecular alignment in the fiber. The consequences of fiber annealing for the climatic stability of certain polymer optical fiber-based sensors are discussed, emphasizing the importance of fiber controlled pre-annealing with respect to the foreseeable operating conditions.

Sensitivity enhancement using annealed polymer optical fibre based sensors for pressure sensing applications

Thermal annealing can be used to induce a permanent negative Bragg wavelength shift for polymer fibre grating sensors and it was originally used for multiplexing purposes. Recently, researchers showed that annealing can also provide additional benefits, such as strain and humidity sensitivity enhancement and augmented temperature operational range. The annealing process can change both the optical and mechanical properties of the fibre. In this paper, the annealing effects on the stress and force sensitivities of PMMA fibre Bragg grating sensors are investigated. The incentive for that investigation was an unexpected behaviour observed in an array of sensors which were used for liquid level monitoring. One sensor exhibited much lower pressure sensitivity and that was the only one that was not annealed. To further investigate the phenomenon, additional sensors were photo-inscribed and characterised with regard their stress and force sensitivities. Then, the fibres were annealed by placing them in hot water, controlling with that way the humidity factor. After annealing, stress and force sensitivities were measured again. The results show that the annealing can improve the stress and force sensitivity of the devices. This can provide better performing sensors for use in stress, force and pressure sensing applications.

Synthesis, Modification, and Application of Siloxane Materials for Environmental Sensing

As human populations and resource consumption increase, it is increasingly important to monitor the quality of our environment. While laboratory instruments offer useful information, portable, easy to use sensors would allow environmental analysis to occur on-site, at lower cost, and with minimal operator training. We explore the synthesis, modification, and applications of modified polysiloxane in environmental sensing. Multiple methods of producing modified siloxanes were investigated. Oligomers were formed by using functionalized monomers, producing siloxane materials containing silicon hydride, methyl, and phenyl side chains. Silicon hydride-functionalized oligomers were further modified by hydrosilylation to incorporate methyl ester and naphthyl side chains. Modifications to the siloxane materials were also carried out using post-curing treatments. Methyl ester-functionalized siloxane was incorporated into the surface of a cured poly(dimethylsiloxane) film by siloxane equilibration. The materials containing methyl esters were hydrolyzed to reveal carboxylic acids, which could later be used for covalent protein immobilization. Finally, the siloxane surfaces were modified to incorporate antibodies by covalent, affinity, and adsorption-based attachment. These modifications were characterized by a variety of methods, including contact angle, attenuated total reflectance Fourier transform infrared spectroscopy, dye labels, and 1H nuclear magnetic resonance spectroscopy. The modified siloxane materials were employed in a variety of sensing schemes. Volatile organic compounds were detected using methyl, phenyl, and naphthyl-functionalized materials on a Fabry-Perot interferometer and a refractometer. The Fabry-Perot interferometer was found to detect the analytes upon siloxane extraction by deformation of the Bragg reflectors. The refractometer was used to determine that naphthyl-functionalized siloxanes had elevated refractive indices, rendering these materials more sensitive to some analytes. Antibody-modified siloxanes were used to detect biological analytes through a solid phase microextraction-mediated enzyme linked immunosorbent assay (SPME ELISA). The SPME ELISA was found to have higher analyte sensitivity compared to a conventional ELISA system. The detection scheme was used to detect Escherichia coli at 8500 CFU/mL. These results demonstrate the variety of methods that can be used to modify siloxanes and the wide range of applications of modified siloxanes has been demonstrated through chemical and biological sensing schemes.

Remote Sensing of Vegetation Change Across a Latitudinal Gradient in the Canadian Arctic

Global air surface temperatures and precipitation have increased over the last several decades resulting in a trend of greening across the Circumpolar Arctic. The spatial variability of warming and the inherent effects on plant communities has not proven to be uniform or homogeneous on global or local scales. We can apply remote sensing vegetation indices such as the Normalized Difference Vegetation Index (NDVI) to map and monitor vegetation change (e.g., phenology, greening, percent cover, and biomass) over time. It is important to document how Arctic vegetation is changing, as it will have large implications related to global carbon and surface energy budgets. The research reported here examined vegetation greening across different spatial and temporal scales at two disparate Arctic sites: Apex River Watershed (ARW), Baffin Island, and Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, NU. To characterize the vegetation in the ARW, high spatial resolution WorldView-2 data were processed to create a supervised land-cover classification and model percent vegetation cover (PVC) (a similar process had been completed in a previous study for the CBAWO). Meanwhile, NDVI data spanning the past 30 years were derived from intermediate resolution Landsat data at the two Arctic sites. The land-cover classifications at both sites were used to examine the Landsat NDVI time series by vegetation class. Climate variables (i.e., temperature, precipitation and growing season length (GSL) were examined to explore the potential relationships of NDVI to climate warming. PVC was successfully modeled using high resolution data in the ARW. PVC and plant communities appear to reside along a moisture and altitudinal gradient. The NDVI time series demonstrated an overall significant increase in greening at the CBAWO (High Arctic site), specifically in the dry and mesic vegetation type. However, similar overall greening was not observed for the ARW (Low Arctic site). The overall increase in NDVI at the CBAWO was attributed to a significant increase in July temperatures, precipitation and GSL.

Fiber-optic vibration sensing of cantilevers immersed in fluids

An all fiber-optical method to monitor densities and viscosities of liquids utilizing a steel cantilever (4 x 0.3 x 0.08 cm3) is presented. The actuation is performed by photothermally heating the cantilever at its base with an intensity-modulated 808 nm diode laser. The cantilever vibrations are picked up by an in-fiber Fabry Perot cavity sensor attached along the length of the cantilever. The fluid properties can be related to the resonance characteristics of the cantilever, e.g. a shift in the resonance frequency corresponds to a change in fluid density, and the width of the resonance peak gives information on the dynamic viscosity after calibration of the system. Aqueous glycerol, sucrose and ethanol samples in the range of 0.79–1.32 gcm−3 (density) and 0.89–702 mPas (viscosity) were used to investigate the limits of the sensor. A good agreement with literature values could be found with an average deviation of around 10 % for the dynamic viscosities, and 5–16 % for the mass densities. A variety of clear and opaque commercial spirits and an unknown viscous sample, e.g. home-made maple syrup, were analyzed and compared to literature values. The unique detection mechanism allows for the characterization of opaque samples and is superior to conventional microcantilever sensors. The method is expected to be beneficial in various industrial sectors such as quality control of food samples.

Building a Rockfall Database Using Remote Sensing: Techniques for Hazard Management in Canadian Rail Corridors

The section of CN railway between Vancouver and Kamloops runs along the base of many hazardous slopes, including the White Canyon, which is located just outside the town of Lytton, BC. The slope has a history of frequent rockfall activity, which presents a hazard to the railway below. Rockfall inventories can be used to understand the frequency-magnitude relationship of events on hazardous slopes, however it can be difficult to consistently and accurately identify rockfall source zones and volumes on large slopes with frequent activity, leaving many inventories incomplete. We have studied this slope as a part of the Canadian Railway Ground Hazard Research Program and have collected remote sensing data, including terrestrial laser scanning (TLS), photographs, and photogrammetry data since 2012, and used change detection to identify rockfalls on the slope. The objective of this thesis is to use a subset of this data to understand how rockfalls identified from TLS data could be used to understand the frequency-magnitude relationship of rockfalls on the slope. This includes incorporating both new and existing methods to develop a semi-automated workflow to extract rockfall events from the TLS data. We show that these methods can be used to identify events as small as 0.01 m3 and that the duration between scans can have an effect on the frequency-magnitude relationship of the rockfalls. We also show that by incorporating photogrammetry data into our analysis, we can create a 3D geological model of the slope and use this to classify rockfalls by lithology, to further understand the rockfall failure patterns. When relating the rockfall activity to triggering factors, we found that the amount of precipitation occurring over the winter has an effect on the overall rockfall frequency for the remainder of the year. These results can provide the railways with a more complete inventory of events compared to records created through track inspection, or rockfall monitoring systems that are installed on the slope. In addition, we can use the database to understand the spatial and temporal distribution of events. The results can also be used as an input to rockfall modelling programs.

Hierarchical Nafion enhanced carbon aerogels for sensing applications

This work describes the fabrication of hierarchical 3D Nafion enhanced carbon aerogels (NECAGs) for sensing applications via a fast freeze drying method. Graphene oxide, multiwalled carbon nanotubes and Nafion were mixed and extruded into liquid nitrogen followed by the removal of ice crystals by freeze drying. The addition of Nafion enhanced the mechanical strength of NECAGs and effective control of the cellular morphology and pore size was achieved. The resultant NECAGs demonstrated high strength, low density, and high specific surface area and can achieve a modulus of 20 kPa, an electrical conductivity of 140 S m(-1), and a specific capacity of 136.8 F g(-1) after reduction. Therefore, NECAG monoliths performed well as a gas sensor and as a biosensor with high sensitivity and selectivity. The remarkable sensitivity of 8.52 × 10(3)μA mM(-1) cm(-2) was obtained in dopamine (DA) detection, which is two orders of magnitude better than the literature reported values using graphene aerogel electrodes made from a porous Ni template. These outstanding properties make the NECAG a promising electrode candidate for a wide range of applications. Further in-depth investigations are being undertaken to probe the structure-property relationship of NECAG monoliths prepared under various conditions.

Structural Health Monitoring Inside Concrete and Grout Using the Wireless Identification and Sensing Platform (WISP)

This research investigates the implementation of battery-less RFID sensing platforms inside lossy media, such as, concrete and grout. Both concrete and novel grouts can be used for nuclear plant decommissioning as part of the U.S. Department of Energy’s (DOE’s) cleanup projects. Our research examines the following: (1) material characterization, (2) analytical modeling of transmission and propagation losses inside lossy media, (3) maximum operational range of RFID wireless sensors embedded inside concrete and grout, and (4) best positioning of antennas for achieving longer communication range between RFID antennas and wireless sensors. Our research uses the battery-less Wireless Identification and Sensing Platform (WISP) which can be used to monitor temperature, and humidity inside complex materials. By using a commercial Agilent open-ended coaxial probe (HP8570B), the measurements of the dielectric permittivity of concrete and grout are performed. Subsequently, the measured complex permittivity is used to formulate analytical Debye models. Also, the transmission and propagation losses of a uniform plane wave inside grout are calculated. Our results show that wireless sensors will perform better in concrete than grout. In addition, the maximum axial and radial ranges for WISP are experimentally determined. Our work illustrates the feasibility of battery-less wireless sensors that are embedded inside concrete and grout. Also, our work provides information that can be used to optimize the power management, sampling rate, and antenna design of such sensors.

Bimodal magneto-luminescent dysprosium (DyIII)-potassium (KI)-oxalate framework: magnetic switchability with high anisotropic barrier and solvent sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy(C₂O₄)₂(H₂O)₄}_n (1) (C₂O₄^2- = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (1′) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound 1 shows solvent responsive bimodal magnetic and luminescence properties related to the DyIII center. Compound 1 exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal-organic frameworks. Both the compounds 1 and 1′ exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for 1 and 418 ± 7 K for 1′) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound 1 shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking 1′ as a potential H₂O sensor.