Fibre Bragg grating strain sensors

The fabrication of in-fibre Bragg gratings (FBGs) and their application as sensors is reported. The strain and temperature characteristic results for a number of chirped and uniform gratings written into three different host fibres are presented. The static and dynamic temperature response of a commercially available temperature compensated grating is reported. A five sensor wavelength division multiplexed fibre Bragg grating strain measurement system with an interrogation rate of 25 Hz and resolution of 10 was constructed. The results from this system are presented. A novel chirped FBG interrogation method was implemented in both the 1.3 and 1.5 m telecommunication windows. Several single and dual strain sensor systems, employing this method, were constructed and the results obtained from each are reported and discussed. These systems are particularly suitable for the measurement of large strain. The results from a system measuring up to 12 m and with a potential measurement range of 30 m are reported. This technique is also shown to give an obtainable resolution of 20 over a measurement range of 5 000 for a dual sensor system. These systems are simple, robust, passive and easy to implement. They offer low cost, high speed and, in the case of multiple sensors, truly simultaneous interrogation. These advantages make this technique ideal for strain sensing in SMART structures. Systems based on this method have been installed in the masts of four superyachts. A system, based on this technique, is currently being developed for the measurement of acoustic waves in carbon composite panels. The results from an alternative method for interrogating uniform FBG sensors are also discussed. Interrogation of the gratings was facilitated by a specifically written asymmetric grating which had a 15 nm long linearly sloped spectral edge. This technique was employed to interrogate a single sensor over a measurement range of 6 m and two sensors over a range of 4.5 me. The results obtained indicated achievable resolutions of 47 and 38 respectively.

Inscription and characterization of waveguides written into borosilicate glass by a high-repetition-rate femtosecond laser at 800 nm

A series of waveguides was inscribed in a borosilicate glass (BK7) by an 11 MHz repetition rate femtosecond laser operating with pulse energies from 16 to 30 nJ and focused at various depths within the bulk material. The index modification was measured using a quantitative phase microscopy technique that revealed central index changes ranging from 5×10-3 to 10-2, leading to waveguides that exhibited propagation losses of 0.2 dB/cm at a wavelength of 633 nm and 0.6 dB/cm at a wavelength of 1550 nm with efficient mode matching, less than 0.2 dB, to standard optical fibers. Analysis of the experimental data shows that, for a given inscription energy, the index modification has a strong dependence on inscription scanning velocity. At higher energies, the index modification increases with increasing inscription scanning velocity with other fabrication parameters constant.

Effectively simultaneous temperature and strain measurement utilising a dual-grating sensor formed by type IA and type IIA FBGs

In this paper, we report a systematic investigation of the dependence of both temperature and strain sensitivities on the jiber Bragg grating (FBG) type, including the wellknown Type I, Type IIA, and a new type which we have designated Type 1.4, using both hydrogen-Ji-ee and hydrogenated B/Ge codoped jibers. We have identijed distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, duul-parameter sensor device. Three dual-grating sensing schemes with different combinations of gruting types have been constructed and compared. The Type IA-Type IIA combination exhibits the best pe$ormance and is superior to that of previously reported gruting-based structures. The characteristics of the measurement errors in such dualgrating sensor systems is also presented in detail.

22km distributed strain sensor using Brillouin loss in an optical fibre

A novel distributed strain sensor is presented utilizing the strain dependence of the frequency at which the Brillouin loss is maximized in the interaction between a cw laser and a pulsed laser. A strain resolution of 20 µ with a spatial resolution of 5 m has been achieved with a 22 km sensing length.

Combined distributed temperature and strain sensor based on Brillouin loss in an optical fiber

We present a novel distributed sensor that utilizes the temperature and strain dependence of the frequency at which the Brillouin loss is maximized in the interaction between a cw laser and a pulsed laser. With a 22-km sensing length, a strain resolution of 20 µ? and a temperature resolution of 2°C have been achieved with a spatial resolution of 5 m.

Engineering of a novel Saccharomyces cerevisiae wine strain with a respiratory phenotype at high external glucose concentrations

The recently described respiratory strain Saccharomyces cerevisiae KOY.TM6*P is, to our knowledge, the only reported strain of S. cerevisiae which completely redirects the flux of glucose from ethanol fermentation to respiration, even at high external glucose concentrations (27). In the KOY.TM6*P strain, portions of the genes encoding the predominant hexose transporter proteins, Hxt1 and Hxt7, were fused within the regions encoding transmembrane (TM) domain 6. The resulting chimeric gene, TM6*. encoded a chimera composed of the amino-terminal half of Hxt1 and the carboxy-terminal half of Hxt7. It was subsequently integrated into the genome of an hxt null strain. In this study, we have demonstrated the transferability of this respiratory phenotype to the V5 hxt1-7Δ strain, a derivative of a strain used in enology. We also show by using this mutant that it is not necessary to transform a complete hxt null strain with the TM6* construct to obtain a nonethanol-producing phenotype. The resulting V5.TM6*P strain, obtained by transformation of the V5 hxt1-7Δ strain with the TM6* chimeric gene, produced only minor amounts of ethanol when cultured on external glucose concentrations as high as 5%. Despite the fact that glucose flux was reduced to 30% in the V5.TM6*P strain compared with that of its parental strain, the V5.TM6*P strain produced biomass at a specific rate as high as 85% that of the V5 wild-type strain. Even more relevant for the potential use of such a strain for the production of heterologous proteins and also of low-alcohol beverages is the observation that the biomass yield increased 50% with the mutant compared to its parental strain. Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Annealing and temperature coefficient study of type IA fibre Bragg gratings inscribed under strain and no strain - Implications to optical fibre component reliability

The annealing properties of Type IA Bragg gratings are investigated and compared with Type I and Type IIA Bragg gratings. The transmission properties (mean and modulated wavelength components) of gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I gratings at 80°C. Extending this work to include the thermal decay of Type IA gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA grating, modifying the temperature coefficient and annealing curves, with the grating showing a remarkable improvement in high temperature stability, leading to a robust grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I grating. Therefore, the combination of Type I and IA (strained) gratings make it possible to decouple temperature and strain over larger temperature excursions.

Simultaneous measurement of strain and curvature using superstructure fibre Bragg gratings

We report the first demonstration of the simultaneous measurement of strain and curvature, with temperature compensation, using a single superstructure fibre Bragg grating (SFBG). The SFBG exhibits the properties of both the fibre Bragg grating (FBG) and the long period fibre grating (LPG) such that its spectral response facilitates strain measurement from the wavelength shift of the FBG-like characteristic, and independent measurement of curvature from the LPG-like mode-splitting characteristic. The dependence of the LPG mode-splitting on the mode order has also been investigated and utilised for the measurement of very small curvatures.

Use of dual-grating sensors formed by different types of fiber Bragg gratings for simultaneous temperature and strain measurements

We report on a systematic investigation of the dependence of both temperature and strain sensitivities on the fiber Bragg grating type, including the well-known Type I, Type IIA, and a new type that we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibres. We have identified distinct sensitivity characteristics for each grating type, and we have used them to implement a novel dual-grating, dual-parameter sensor device. Three dual-grating sensing schemes with different combinations of grating type have been constructed and compared, and that of a Type IA-Type IIA combination exhibits the best performance, which is also superior to that of previously reported grating-based structures. The characteristics of the measurement errors in such dual-grating sensor systems is also presented in detail. © 2004 Optical Society of America.

Pseudoperiodic "Living" and/or controlled cationic ring-opening copolymerization of oxetane with tetrahydropyran:microstructure of polymers vs kinetics of chain growth

The "living" and/or controlled cationic ring-opening bulk copolymerization of oxetane (Ox) with tetrahydropyran (THP) (cyclic ether with no homopolymerizability) at 35°C was examined using ethoxymethyl-1 -oxoniacyclohexane hexafluoroantimonate (EMOA) and (BF3 · CH3OH)THP as fast and slow initiator, respectively, yielding living and nonliving polymers with pseudoperiodic sequences (i.e., each pentamethylene oxide fragment inserted into the polymer is flanked by two trimethylene oxide fragments). Good control over number-average molecular weight (Mn up to 150000 g mol-1) with molecular weight distribution (MWD ∼ 1.4-1, 5) broader than predicted by the Poison distribution (MWDs > 1 +1/DPn) was attained using EMOA as initiating system, i.e., C 2H5OCH2Cl with 1.1 equiv of AgSbF6 as a stable catalyst and 1.1 equiv of 2,6-di-tert-butylpyridine used as a non-nucleophilic proton trap. With (BF3 · CH 3OH)THP, a drift of the linear dependence M n(GPC) vs Mn(theory) to lower molecular weight was observed together with the production of cyclic oligomers, ∼3-5% of the Ox consumed in THP against ∼30% in dichloromethane. Structural and kinetics studies highlighted a mechanism of chains growth where the rate of mutual conversion between "strain ACE species" (chain terminated by a tertiary 1-oxoniacyclobutane ion, Al) and "strain-free ACE species" (chain terminated by a tertiary 1-oxoniacyclohexane ion, Tl) depends on the rate at which Ox converts the stable species T1 (kind of "dormant" species) into a living "propagating" center A1 (i.e., k aapp[Ox]). The role of the THP solvent associated with the suspension of irreversible and reversible transfer reactions to polymer, when the polymerization is initiated with EMOA, was predicted by our kinetic considerations. The activation -deactivation pseudoequilibrium coefficient (Qt) was then calculated in a pure theoretical basis. From the measured apparent rate constant of Ox (kOxapp) and THP (kTHPapp = ka(endo)app) consumption, Qt and reactivity ratio (kp/kd, k a(endo)/ka(exo), and ks/ka(endo) were calculated, which then allow the determination of the transition rate constant of elementary step reactions that governs the increase of Mu with conversion. © 2009 American Chemical Society.

Seawater carbonate chemistry, growth rate and PIC and POC production during experiments with Emiliania huxleyi (B92/11), 2011

The coccolithophore Emiliania huxleyi was cultured under a broad range of carbonate chemistry conditions to distinguish the effects of individual carbonate system parameters on growth, primary production, and calcification. In the first experiment, alkalinity was kept constant and the fugacity of CO2(fCO2) varied from 2 to 600 Pa (1Pa ~ 10 µatm). In the second experiment, pH was kept constant (pHfree = 8) with fCO2 varying from 4 to 370 Pa. Results of the constant-alkalinity approach revealed physiological optima for growth, calcification, and organic carbon production at fCO2 values of ~20Pa, ~40 Pa, and ~80 Pa, respectively. Comparing this with the constant-pH approach showed that growth and organic carbon production increased similarly from low to intermediate CO2 levels but started to diverge towards higher CO2 levels. In the high CO2 range, growth rates and organic carbon production decreased steadily with declining pH at constant alkalinity while remaining consistently higher at constant pH. This suggests that growth and organic carbon production rates are directly related to CO2 at low (sub-saturating) concentrations, whereas towards higher CO2 levels they are adversely affected by the associated decrease in pH. A pH dependence at high fCO2 is also indicated for calcification rates, while the key carbonate system parameter determining calcification at low fCO2 remains unclear. These results imply that key metabolic processes in coccolithophores have their optima at different carbonate chemistry conditions and are influenced by different parameters of the carbonate system at both sides of the optimum.

Seawater carbonate chemistry and processes during experiments with phytoplankton Emiliania huxleyi (strain Bergen 2005), 2010

The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented for acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment. The exact number of generations required for acclimation to CO2-induced changes in seawater carbonate chemistry, however, is unknown. Here we show that Emiliania huxleyi's short-term response (26 h) after cultures (grown at 500 µatm) were abruptly exposed to changed CO2 concentrations (~190, 410, 800 and 1500 ?atm) is similar to that obtained with acclimated cultures under comparable conditions in earlier studies. Most importantly, from the lower CO2 levels (190 and 410 ?atm) to 750 and 1500 µatm calcification decreased and organic carbon fixation increased within the first 8 to 14 h after exposing the cultures to changes in carbonate chemistry. This suggests that Emiliania huxleyi rapidly alters the rates of essential metabolical processes in response to changes in seawater carbonate chemistry, establishing a new physiological "state" (acclimation) within a matter of hours. If this relatively rapid response applies to other phytoplankton species, it may simplify interpretation of studies with natural communities (e.g. mesocosm studies and ship-board incubations), where often it is not feasible to allow for a pre-conditioning phase before starting experimental incubations.