Sensor, temporal resolution

Ruzicka ei al. [57,58] developed some peculiar reflectance flow-through biosensors based on a sensing microzone accommodating an enzyme and an acid-base indicator (both in immobilized form) where spacial and temporal resolution of the biochemical and chemical reaction or the reversible separation of hydrogen ions was therefore impossible. The pH sensors developed by these authors (see Section 3.5.1.1) can be regarded as precedents for these reflectance sensors. The sensing approach used relies on... 

The factors that influence the chemical resolution of sensors are well understood and are not discussed here. This section reviews the factors that control the temporal resolution of sensors to be used for eddy correlation. In the analysis of the design of chemical sensors to be used for eddy correlation it is instructive to consider the different components of chemical sensor systems separately to determine the influences that they have on the temporal response to variations in the atmospheric concentration of a trace constituent. Of course this analysis is an oversimplification because the total systems operate in a more complex fashion, but it is a useful exercise. 

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. 

Among the different chemosensors, those which are fluorescence-based present many advantages such as high sensitivity (single molecule detection is possible), low cost, ease of performance, and versatility. The fluorescent-based sensors offer subnanometer spatial resolution with submicron visualization and submillisecond temporal resolution.20-26 Thus, numerous fluorescence-based chemosensors have been prepared and investigated.4-6 On the other hand, chromoionophores are also distinct and worthwhile subjects in their own right27-30... 

Shear stress measurement plays an important role for characterization and control of both macro-and microscale flows. There are various existing techniques suitable for either steady state or instantaneous nature of the flow. The rapid development of MEMS manufacturing technology has immensely contributed to improvement in spatial and temporal resolution of shear stress sensors. Therefore, turbulent flow control has become feasible for many practical apphcations. However, the cahbration and implementation issues of shear stress measurements are not completely estabhshed. Therefore, the implementation procedure for shear stress measurement is problem specific and requires complete understanding of the measurement principle. The existing shear stress measurement technologies have not been implemented over a wide range of microscale flow problems. Therefore, future research should concentrate on critical issues relevant to shear stress measurement in various microflow applications. This wfll contribute towards development of matured shear stress measurement techniques. 

Advances in instrumentation and communications (for data transmission) have increased the reUabi-lity of continuous monitors. Such systems can be deployed in remote and hazardous locations to provide high temporal resolution chemical data in aquatic and atmospheric environments. Examples include sensors for monitoring nutrients in rivers, instrumented buoys for oceanographic mapping, and... 

Fluorescent sensors in solution (chemosensors) and fiberoptic sensors. Fluorescence is a particularly important technique in this field because of its high sensitivity of detection down to a single molecule, subnanometer spatial resolution with submicrometer visualization and submillisecond temporal resolution. 

Despite promising, the reliability of implantable systems is often undermined by factors like biofouling [100, 101] and foreign body response [102] in addition to sensor drifts and lack of temporal resolution [103]. To minimize such problems. 

Figure 29.6 On-engine TDLAS monitoring of CO2 transient dynamics within the air intake manifold of production internal combustion engines. Left principle of the fibre-coupled sensor set-up right sensor incorporated into an actual manifold inset CO2 concentration measurement, with 1 s temporal resolution. Adapted from Sonnenfroh etal, 30th Int. Symp. on Combustion, 2004, with permission of Physical Sciences Inc...

As these requirements are rather complex, the advent of luminescent signalling systems and luminescent-based devices continues to bring about many advantages, since fluorescence measurements are usually very sensitive, low cost, easily performed and versatile, offering submicron visualisation and submillisecond temporal resolution. Consequently, luminescent chemical sensors play a major role in key fields such as industry, diagnostic and therapeutic medicine, and various kinds of environmental monitoring. 

Hot-wire anemometers have traditionally been applied in the fields of experimental fluid mechanics and aerospace engineering. Despite the possibilities to measure real-time physical parameters such as temperature, velocity, flow rates, and shear stress, the spatial resolution is limited to the device dimension. The advent of MicroElectroMe-chanical system (MEMS) and nano-scale thermal sensors has revolutionized the spatial and temporal resolution critical to gain entry into micro-fluidics, micro-circulation, biomedical sciences, and cardiovascular medicine. These micro/nano devices are fabricated with the Semiconductor-... 

More recently, solid-state and optical sensors for humidity and oxygen detection have been reported (Khijwania et al., 2005 Steele et al., 2006, 2009 Lee et al, 2009 Inman et al., 2010). These sensors are small, chemically stable, and minimally intrusive in typical PEMFC environments. They also enable transient measurements that approach the temporal resolution provided by available electrochemical and data-acquisition hardware (<1 s). 

Temporal Resolution. Due to the high-gain amplifiers incorporated into the Wheatstone bridge, CTA systems offer a very high frequency response, reaching into the range of hundreds of kilohertz. This makes CTA an ideal instrument for the measurement of spectral content in most flows. A CTA sensor... 

---