Optical fibres technique

M.N. Tib and R. Narayanaswamy, Multichannel calibration technique for optical-fibre chemical sensor using artificial neural network. Sensors Actuators, B39 (1997) 365-370. 

Most dyes, including sulfonated azo dyes, are nonvolatile or thermally unstable, and therefore are not amenable to GC or gas-phase ionisation processes. Therefore, GC-MS techniques cannot be used. GC-MS and TGA were applied for the identification of acrylated polyurethanes in coatings on optical fibres [295]. Although GC-MS is not suited for the analysis of polymers, the technique can be used for the study of the products of pyrolysis in air, e.g. related to smoke behaviour of CPVC/ABS and PVC/ABS blends [263],... 

This chapter reviews the development of optical gas sensors, starting with an initial emphasis on optical-fibre remoted techniques and finishing with a particular focus on our own group s work on highly selective methods using correlation spectroscopy. This latter section includes extensive theoretical modelling of a correlation spectroscopy method, and compares theory with practice for a CO2 sensor. 

Gas detection methods may be split into two groups, (i) direct methods, which monitor a physical parameter of the target gas, and (ii) indirect methods, which use a chemical reaction or indicator to show the concentration of the gas being sensed. This division of methods may be further split into optical sensing techniques and non-optical techniques. This review will predominantly focus on direct optical-spectroscopy fibre sensing techniques. 

A general review of optical gas sensing techniques, particularly optical fibre-based ones, has been presented to set the scene, before finishing with a more detailed description of our own methods using correlation... 

The application of near-IR spectroscopy for real-time monitoring of glucose, lactic acid, acetic acid and biomass in liquid cultures of microorganisms of the genera Lactobacillus and Staphylococcus has been recently published [76]. The NIR spectrum acquired by the optical-fibre probe immersed in the culture is exploited using a partial least squares (PLS) calibration step, a classical method for IR techniques. 

K. I. White, Practical application of the refracted-near-field technique for the measurement of optical fibre refractive index profiles. Optic and Quantum Electronics 11, 185-196 (1979). 

Another sensor based on a fiber-optic-based spectroelectrochemical probe uses a DNA/ethidium bromide system to take advantage of the biological recognition processes [92]. The concept of immobilizing electrochemical reagents on the end of an optical fibre is a useful addition to the field of bioanalytical sensors. Before this development, optical and electrochemical detection of DNA were performed separately. Optical and electrochemical detection of DNA are suitable for a DNA detection system [93, 94] and these techniques will enable a production of a cheap DNA biosensor with a rapid and quantitative response. 

Optoelectronic components for remote control and monitoring and for data transmission are being installed in hazardous areas more and more. In particular, the optical-fibre transmission technique enables numerous modem applications. Apart from the great advantages of this technology, the risk of an ignition caused by optical radiation at a power level sufficiently high is to be taken into account (see Section 1.2.7). 

Environmental monitoring has also taken advantage of acoustic levitation for the investigation of physico-chemical processes relevant to the troposphere — mainly at temperatures below 0°C. Gas-liquid transfer of H2O2 from the gas phase to the levitated droplet was studied from in situ chemiluminescence measurements. Also, freezing of stably positioned droplets was observed by means of a microscope and a video camera, and the usefulness of this technique for simulation and investigation of cloud processes thus demonstrated. Ex situ microanalysis of sub-microlitre droplets by the use of an optical fibre luminometer also proved an effective means for investigating important physicochemical processes at the micro scale [100]. 

Mignot, L., Junter, G.A. and Labbe, M. (1989). A new type of immobilized-cell photobioreactor with internal illumination by optical fibres. Biotechnol. Techniques 3,299-304. 

Lyons, W. B. Lewis, E. Neural Networks and Pattern Recognition Techniques Applied to Optical Fibre Sensors. Trans. Inst. Measurm. Control 2000, 22, 385 104... 

In general, a vast number of optical transduction techniques can be used for biosensor development. These may employ linear optical phenomenon (e.g. adsorption, fluorescence, phosphorescence, and polarization) or nonlinear phenomena (e.g. second harmonic generation). The choice of a particular optical method depends on the analyte and the sensitivity needed. Total internal reflection fluorescence (TIRF) has been used with planar and fibre-optic wave-guides as signal transducers in a number of biosensors. 

As discussed later, in Section 3.4, this technique is particularly well adapted to coupling to optical fibres, so a probe that can be immersed in a polymer reaction stream may be fabricated to enable spectra to be collected in real time. The principles of total internal reflection and its application in fibre-optics are discussed in more detail in Section 3.4.1. 

At about the same time as these concerns were expressed, the optimization of an optical-fibre system for use in remote Raman spectroscopy was described (Hendra et al, 1988). The areas explored are similar to those for remote emission spectroscopy discussed earlier in Section 3.4.2, and techniques for achieving the efficient transfer of the weak scattered radiation to the gathering probe include the use of... 

Lee and Cho (2005) developed a cure model for UV nano-imprinting. It was shown via fibre-optic FTIR techniques (as developed by Decker and Moussa (1990)) that the degree of cure had an exponential relation to the UV-irradiation time, power and temperature. 

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