Optical sensor

Temperature sensors for providing closed-loop feedback for APFC are being developed by Stanford University for the measurement of combustion species and temperature. Laser-diode sensors offer nonintrusive measurements of the combustion exit plane temperature pattern. A detailed description of the sensor measurement methodology can be found in the literature [1, 2]. There is 

Most MIP optical sensors reported in the literature utilize fluorescence as the detectable signal [215, 216]. With fluorescent analytes, the fluorescence of the MIP will increase upon binding [217, 218]. With non-fluorescent analytes, a fluorescent reporter molecule can be applied. The reporter molecule competes with or is displaced by the analyte [219-221]. Alternatively, a fluorescent monomer can be incorporated in the polymer network [222]. Upon binding of the analyte, the fluorescence of the MIP is altered. 

Another approach for MIP sensors is detection based on surface plasmon resonance (SPR) [223-225]. The strategy is to synthesize the MIP on a gold or silver 

An optode is a chemical sensor based on an optical fiber. To understand how optodes work, we first need to know a little about refraction of light. 

The speed of light in a medium of refractive index n is chi, where c is the speed of light in vacuum. That is, for vacuum, n = 1. Refractive index is commonly measured at 20°C at the wavelength of the sodium D line (A = 589.3 nm). The frequency of light, v, inside a medium does not change from the frequency in vacuum. Because the speed of light, chi, inside a medium decreases from that of vacuum, the wavelength decreases so that Av = c/n. 

In a ferroelectric material, the dipole moments of molecules remain aligned in the absence of an external field. This alignment gives the material a permanent electric polarization. 

Infrared radiation promotes electrons from the valence band of silicon to the conduction band. Semiconductors that are used as infrared detectors have smaller band gaps than silicon 

Solution The refractive index for air is close to 1, and for water, 1.33. From Snell s law, 

Interaction of electromagnetic radiation with matter occurs over a broad range of frequencies and usually in a highly specific way (Table 9.1). Study and use of these interactions is in the domain of spectroscopy, which provides information ranging from the electronic structure of atoms to dynamics of polymeric chains. 

Janata, Principles of Chemical Sensors, DOI 10.1007/978-0-387-69931-8 9, Springer Science+Business Media, LLC 2009 

Region Wavenumber Oam-1) Wavelength (pm) Transition Information Energy (kJ/mol) 

The concept of dual character of light is particularly relevant to the discussion of optical sensors. In this introductory section, the basic quantized (corpuscular) aspects of light as they relate to optical sensors are reviewed first, followed by a brief review of physics of optical waveguides and optical fibers which rely on wavelike (continuous) properties of light. Detailed information can be found in analytical (e.g., Skoog et al., 1998) and specialized textbooks (e.g., Hollas, 2004). 

In corrosion applications, pH gradients have been tentatively measured using fluoresceine or fluoresceinamine. For fluoresceine excitation is at 488nm and emission is at 515nm. 

CLSM and Near-Field Scanning Optical Microscopy has been used by R.W Smyrl to map the fluorescence during corrosion of 2024 and 6061 aluminium alloys. It has been shown that on 6061 alloy fluorescence is emitted from the Al-Mg-Si intermetal-lics. The fluorescence is in fact trapped by the corrosion products (Fig. 9a) due to the selective dissolution of Mg it is an indirect 

FOCS (fiber bundle) was used by S.Szunerits et D.Walt to image the concentration of Al cations during localized dissolution of pure aluminium in this case the fluorescent molecule was morin (excitation 3 lOnm - emission 510 mu) which allowed the in situ visualization of the corrosion processes by monitoring the release of Al. Nevertheless, application of FOCS for corrosion mechanisms has not been deeply investigated in the mentioned work but this kind of sensor represents a promising tool which could be applied. 

How to Image In-Situ the Galvanic Current Distribution Scanning Vibrating Electrode Technique 

The potential drop measured by the microelectrode is converted with the Ohm s law into a current density value after amplification. The displacement of the microelectrode is performed using a motorized and computer controlled XYZ micromanipulator (see Fig. 11a). To improve the application in case of localized cor- 

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Technology has been introduced for on-line estimation of the kappa number based on absorption of ultraviolet light (35). This breakthrough ia optical sensor technology permits closed-loop feedback control of digesters from on-line measurement of the kappa number. 

Optical Fibers. Pure and doped fused siHca fibers have replaced copper lines in the telecommunication area. Eused siHca fibers are used in laser surgery, optical sensor appHcation, and laser welding (see Sensors). Optical-fiber-tethered weapons such as fiber-optics-guided (EOG) missiles are another potential appHcation for fused siHca (249,250) (see Eiberoptics). 

Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

OT1442 A fibre optic sensor for flexible pipeline and riser integrity momtonng... 

Carbon monoxide and carbon dioxide can be measured using the FTIR techniques (Fourier transform infrared techniques see the later section on the Fourier transform infrared analyzer). Electrochemical cells have also been used to measure CO, and miniaturized optical sensors are available for CO 2 monitoring. 

This type of isolation device (also called a chemical barrier) is similar to deflagration suppression systems used on process equipment. This barrier system consists of an optical sensor, installed in the pipeline or duct between two items of equipment, that detects an oncoming deflagration... 

Heterocycles as ligands in ionophores for potentiometric and optical sensors 98CRV1593. 

Optical sensors and relay switches are used throughout the test routine for verification. For all possible problems, as well as the sequence in which they occur, the robot must recognize that there is a problem, define the problem, decide how best to resolve the problem, perform the necessary operations to overcome the problem, and enable the system to resume testing. This is an AI application area and a critical feature, mainly because the system operates unattended and measurements are taken overnight and during weekends. 

Nanosize particles (e.g., metals, semiconductors, etc.) are of continuing interest because they possess fascinating catalytic, electronic, and optical properties. Larger particles decorated with smaller nanoparticles on their surface are of interest because of their potential use as heterogeneous catalysts and their relevance in electronic and optical sensor applications as well as surface-enhanced Raman scattering [39,72-75]. 

Multiple options for data input, the most important of which are machine read and thus obviate the bottleneck that often occurs in data entry. The two main options are Optical Mark Read (bubble) forms, and Smart-Pen , a special pen with an optical sensor that records each keystroke (Fig. 23.2). Both utilize paper case report forms, for which sites have indicated a strong preference over the requirement to enter data on a keyboard. 

Figure 23.2 The SmartPen system is a pen with an optical sensor that records each keystroke on a special form. The pen is docked at a computer or data can be wirelessly transmitted, and data from anywhere in the world are immediately sent for validation. Queries are generated within minutes, closing the feedback loop and markedly rednc-ing query rates as compared to conventional systems.

Elosua, C., Bariain, C., Matias, I.R., Arregui, F.J., Luquin, A., Vergara, E. and Laguna, M. (2008) Indicator immobilization on Fahry-Perot nanocavities towards development of fiber optic sensors. Sensor and actuators B, 130, 158-163. 

Capacitance or conductance measurement This method is applied where the working fluid acts as a capacitive or conductive element in a circuit (Jones et al., 1981). Use of fiber optics sensors has been developed recently (Moujaes and Dougall, 1987, 1990). These methods are used to measure film thickness in annular flow. Further discussion appears in Section 3.3.4.4. For other regimes, the use of the electrical impedience imaging method has also been introduced (Lin et al., 1991). 

Measurement by means of a wall optical sensor The thickness of a film and the slope of its free surface can also be measured by means of a wall optical sensor, as proposed by Ohba et al. (1984). This sensor consists of a cluster of seven optical fibers mounted flush with the wall (Fig. 3.33). A laser beam passed through the central fiber is reflected by the free surface onto the other fiber tips, which collect the light and transmit it to two photodiodes. The light intensities received by these two detectors enable the film thickness and the inclination angle to be determined. 

Figure 3.33 Measurement of liquid film thickness by means of a wall optical sensor as used by Ohba et al. (1984). (From Del-ha ye, 1986. Copyright 1986 by Hemisphere Publishing Corp., New York. Reprinted with permission.)... 

Kam, N.W.S. and Dai, H.J. (2005) Carbon nanotubes as intracellular protein transporters generality and biological functionality. Journal of the American Chemical Society, 127 (16), 6021-6026. Heller, D.A. et al. (2005) Single-walled carbon nanotube spectroscopy in live cells towards long-term labels and optical sensors. Advanced Materials, 17 (23), 2793-2799. 

Liebsch G, Klimant I, Krause C, Wolfbeis OS (2001) Fluorescent imaging of pFl with optical sensors using time domain dual lifetime referencing. Anal Chem 73 4354 -363... 

Resonant photoacoustic gas spectrometry was adapted to fiber optic sensor technology32 as early as in 1984. A Mach-Zehnder arrangement was combined with a resonant photoacoustic cell for gap analysis. The pollutant gas NO2 was detectable in a concentration of 0.5 ppm. In a smart optical fiber hydrogen sensor, the fiber is coated with palladium metal which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometry33. 

Following the discovery that the fluorescence of metalloporphyrins is strongly quenched by oxygen57, optical sensor membranes were developed that are suitable for phosphorescent sensing of oxygen58. Table 1 summarizes fundamental articles on optical sensors for oxygen until the year 2000. 

Hesse 1974 first fiber optic sensor also measures decay time... 

Kopelman et al.73 have prepared fiber optic sensors that are selective for nitric oxide and do not respond to most potential interferents. Both micro-and nanosensors have been prepared, and their response is fast (<1 s), reversible, and linear up to 1 mM concentrations of nitric oxide. The respective "chemistry" at the fiber tip was contacted with the sample, light was guided to the sample through the microfiber, and emitted light was collected by a microscope (without the use of fibers, however). 

As the potential of optical fiber probes for pH measurements was rapidly recognized, several other articles appeared within a few years75 83. Most were reflectance-based, and Seitz reported the first fluorescent pH sensors84, 78. The article by Janata85 on whether pH optical sensors can really measure pH is another "must" in the early literature since it points to aspects hardly addressed in pH sensor work. 

Petersons pH probe also was modified in order to give a miniature fiber optic sensor potentially suitable for glucose measurements90. Kopelman et al.91 developed a fiber-optic pH nanosensor for physiological measurements using a dual-emission sensitive dye. The performance of a pH sensor was reported92. An unclad fiber was dip-coated with a thin layer of porous cladding within which a pH-sensitive dye was entrapped. The fundamental... 

Table 2. Fundamental Work on pH Optical Sensors until the Year 2000.

Later, it was discovered138 that the FAD coenzymes of certain oxidases display large changes in their fluorescence if exposed to their substrates. Thus, the fluorescence of the FAD unit of lactate mono-oxygenase changes substantially on loading with lactate, and this can serve as the analytical information in an optical sensor. 

A novel fiber optic sensor concept using antibody-antigen reactions at a glass-liquid interface was reported by Daehne146. The reaction of antibodies immobilized onto the surface of fused silica fiber optic or planar waveguides with antigens in solution was detected by interaction with the evanescent wave. By detecting in-line fluorescence, the measurement of human IgG is described. 

Many of those working on optical sensors have been overoptimistic. While many chemical sensors and biosensor have found applications in the laboratory and in research, they are much less often applied than physical sensors, e.g. those for temperature, pressure, velocity, or strain. This may be due to several factors, of which the following are considered to be most significant ... 

Other medical products based on optical sensor technology include those of Cardiomed (System 4000), Puritan-Bennett, and one of Radiometer (Copenhagen) which has been withdrawn meanwhile. Optical (but non-fiber) sensors for oxygen and for C02 also are widely used for the determination of bacteria in blood. In 1986, Gehrich et al.36 described an optical fluorescence... 

Table 4 below summarizes the commercial fiber optical sensors that have come to our attention. 

Ivanov V.N., Ivanov S.V., Kel baHkhanov B.F., Klimova L.G., Trubnikov B.N., Chemyi V.V., Elisashvili D.T., Measurement of temperature and salinity variations of water with a fiber-optical sensor, Fizika Atmosfery i Okeana 1985 21 555. 

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