Sensing volume

Also here the small sensing volume makes this kind of sensors attractive devices for high-sensitivity sensing and detection down to the single molecule level. 

D. S. Garmatyuk and R. M. Narayanan, Ultra wide-band continuous-wave random noise arc-SAR , in IEEE Transactions on Geoscience and Remote Sensing, Volume 40, Issue 12, Dec. 2002, pp. 2543-2552. 

A Dispersion occurring in the detector cell, or in the sensing volume of the detector, which can be considered to contribute a variance, (o )... 

The requirements for chemical sensors suitable for use in eddy correlation direct measurements of surface fluxes are examined. The resolution of chemical sensors is examined and defined in terms of surface flux and commonly measured micrometeorological parameters. Aspects of the design and operation of sensor systems are considered. In particular, the effects of the inlet ductingy the sensing volume, and the signal processing on the ability to measure surface fluxes were analyzed. 

Sensing Volume. The sensing volume of a sensor is the volume where the air is actually monitored. The sensing volume is the reaction chamber of a flame photometric detector or a chemiluminescence device, the field of view of an open-path sensor, or the White cell of a reduced-pressure optical system. The residence time of the sample within the sensing volume ultimately limits the temporal resolution of most chemical sensors. 

Two other passive mechanisms that have been studied which involve films that are thicker than the evanescent field free-volume filing and dissolution. These thicker films shield the evanescent field from many enviromnental effects and offer greater sensing volume for increased sensitivity and selectivity. 

Clearly, the LSP resonance is also sensitive to the local refractive index (relative permittivity), and LSP have been studied for applications to SPR sensing as well [4]. One advantage of LSP is that the sensing volume is reduced to the local environment and so a smaller limit of detection and greater multiplexing are possible. 

It is clear that reducing dispersion to these low limits places strict demands on detector design. The solutes are actually sensed in the sensor cell or sensing volume of the detector but must be carried to... 

It is seen that the basic sensor is, indeed, very simple and the top design can be easily constructed to have an effective sensing volume of a few microliters. The lower sensors consist of short lengths of stainless steel tubing (about 0.020 in I.D. and 1/16 in O.D). The two tubes fit into a PTFE tube and the space between the two tubes constitutes the actual sensing volume. The lower sensor is basically the same, but two lengths of tube are employed, both of which are isolated... 

The electrochemical detector in the form described above is extremely sensitive but suffers from a number of drawbacks. Firstly, the mobile phase must be extremely pure and in particular free of oxygen and metal ions. A more serious problem arises, however, from the adsorption of the oxidation or reduction products on the surface of the working electrode. The consequent electrode contamination requires that the electrode system must be frequently calibrated to ensure accurate quantitative analysis. Ultimately, the detector must be dissembled and cleaned, usually by a mechanical abrasion procedure. Much effort has been put into reducing this contamination problem but, although diminished, the problem has not been completely eliminated particularly in the amperometric form of operation. Due to potentially low sensing volume the detector is very suitable for use with small bore columns. 

In addition to the dispersion that takes place during the normal function of the column, dispersion can also occur in connecting tubes, injection system, and detector sensing volume, and as a result of injecting a finite sample mass and sample volume onto the column. 

For the optical particle counter of Fig. 6.5, the sensing volume is 1.5 x 1.5 x mm. Determine the total energy scattered by the air molecules in the volume. Compare this with the scattering by single particles with diameters ranging from 0.05 to 5 / m and a refractive index of 1.5. Assume k = 0.5 m and express your answers in terms of the incident intensity. The temperature is 20 0,... 

Fig. 10 Dual photomultiplier scheme for fluorescent detection. EP - emitted photon stream from the sensing volume, PS - fiberoptic power splitter, ND -neutral density Alter, PMTx -photomultiplier, El, E2,...

However, optimal detection of fluorescence requires careful consideration of both the optical geometry and selective optical filtering of the raw photon flux emanating from the sensing volume. The optical receiver can be separated into a front end which maximizes collection of all emitted photons from the sensing volume and a back end which incorporates selective optical filtering to minimize the out off band emission. These two parts can be independently optimized. 

The above detection limit calculation is based on homogeneously distributed fluorophore molecules in the sensing volume. However, in practice, the probe molecules will be bound to the capillary surface, resulting in considerable decrease in the detection limit, assuming a one-to-one mapping into target molecules. The number of surface bound probes Mpm is given by... 

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