Sensor intrinsic optical

Optical sensors rely on optical detection of a chemical species. Two basic operation principles are known for optically sensing chemical species intrinsic optical property of the analyte is utilized for its detection indicator lor label) based sensing is used when the analyte has no intrinsic optical property. For example, pH is measured optically by immobilizing a pH indicator on a solid support and observing changes in the absorption or fluorescence of the indicator as the pH of the sample varies with time1 20. 

The intrinsic sensors are based on the direct recognition of the chemicals by its intrinsic optical activity, such as absorption or fluorescence in the UV/Vis/IR region. In these cases, no extra chemical is needed to generate the analytical signal. The detection can be a traditional spectrometer or coupled with fiber optics in those regions. Sensors have been developed for the detection of CO, C02 NOx, S02, H2S, NH3, non-saturated hydrocarbons, as well as solvent vapors in air using IR or NIR absorptions, or for the detection of indicator concentrations in the UV/ Vis region and fluorophores such as quinine, fluorescein, etc. 

The interaction phenomenon of the analyte with radiation is governed or modifies the principle on which light is transmitted through the waveguide. Depending on that interaction, we can differentiate three basic types of intrinsic optical sensors [82] refractive-index-type sensors, luminescence-based sensors and absorption-type sensors. 

Keywords Fiber optic sensors Chemical sensors Biosensors Evanescent field sensor Intrinsic fiber optic sensors Multimode fibers Modal power analysis Modal power distribution Spatial intensity modulation Optical far-held pattern... 

Based on the basic performance of optic fiber sensors, Krohn (1986) divided optic fiber sensors into two basic classes. In the first class, the transmission of the fiber is directly affected by the physical phenomena being sensed and is referred to as an intrinsic optic fiber sensor. The second class is for optic fiber position sensors which detect position changes and are sensitive to changes in physical property. There are usually five types of sensors according to their different working principles intensity modulated, transmitting, reflective, micro bending... 

Fig. 5.6. (a) Extrinsic optical fiber sensor, where fibers are used to guide input and output signals, (b) Intrinsic optical fiber sensor, where sensor is incorporated into fiber structure... 

Only a limited number of biochemical analytes have an intrinsic optical absorption that can be measured with sufficient selectivity directly by spectroscopic methods. Other species, particularly hydrogen, oxygen, carbon dioxide, and glucose, which are of primary interest in diagnostic applications, are not susceptible to direct photometry. Therefore, indicator-mediated sensors have been developed using specific reagents that are properly immobilized on the surface of an optical sensor. 

The optical fibre and sensors, intrinsically brittle, will be protected by the structure. 

Optical sensors fall into two categories (1) direct sensors, where the analyte is detected directly via some intrinsic optical property (2) indirect sensors, where the... 

Fiber-optic chemical sensors can be divided into two categories based on their structure (a) Intrinsic sensors are based on the analyte s intrinsic optical properties, and (b) extrinsic sensors are based on sensing materials (chemical or biological) immobilized to the fiber surface, with... 

Fiber-optic sensors are divided into intrinsic and extrinsic sensors. Intrinsic sensors use the individual characteristics of the fiber. For example, interferometric sensors exploit the phase changes of the transmitted light. Such sensors can detect variations in pressure, temperature, and magnetic field. In contrast, extrinsic sensors use an... 

In practice, very few applications of FEWS sensors can be found outside laboratory applications and demonstration systems. In the near-IR, suitable fibres are readily available but usually there is no real necessity to use them. Possible transmission pathlengths are sufficiently large to allow using standard transmission probes, while turbid samples can be measured using transflection or diffuse reflection probes. In the mid-IR, high intrinsic losses, difficulties in fibres handling and limited chemical and mechanical stability limit the applicability of optical fibres as sensor elements. 

Preliminary research has shown that Brillouin fiber-optic sensing systems provide a possible method to detect leaks and third-party intrusion on a pipeline over distances of 25 km or more. Their intrinsic response to both temperature and mechanical strain allows for the separation of these parameters and the detection of anomalies in the scan profiles. In addition, the same sensor could be integrated into the pipeline system to detect possible ground movement relative to fixed reference points. Limited test results on surface loads associated with the intrusion of vehicles and people on a pipeline have demonstrated the sensitivity of the system and its ability to discriminate loads at different soil depths. 

Intrinsically conducting polymers, 13 540 Intrinsic bioremediation, 3 767 defined, 3 759t Intrinsic detectors, 22 180 Intrinsic fiber-optic sensors, 11 148 Intrinsic magnetic properties, of M-type ferrites, 11 67-68 Intrinsic photoconductors, 19 138 Intrinsic rate expressions, 21 341 Intrinsic semiconductors, 22 235-236 energy gap at room temperature, 5 596t Intrinsic strength, of vitreous silica, 22 428 Intrinsic-type detectors, cooling, 19 136 Intrinsic viscosity (TV), of thermoplastics, 10 178... 

Fig. 20a.2. Optical sensor configurations (a) intrinsic sensors, (b) mediator assistant chemical sensor, and (c) chemical sensor-based biosensor.

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