Sensor applications environment control

Acoustic-wave devices are sensitive to a large number of physical and chemical measurands. These include such parameters as temperature, pressure, acceleration, stress, and the adjacent medium s density, viscoelastic properties, and electrical conductivity. Indeed, it is this wide range of measurand sensitivities that makes AW devices attractive for a wide variety of sensor applications. However, since one is interested in exploiting only one of these sensitivities for a particular application, all other responses become undesirable interferences. Thus, it is essential that the sensor environment be carefully controlled to eliminate the effects of sensor cross-sensitivities. 

The development of new NO, sensors has been driven by the strong demand of the automotive and combustion industries worldwide. Figure 3.3 shows market trends of the automotive exhaust gas sensors since 2003. The worldwide production of vehicles will presumably reach saturation by 2010 [5,8], in contrast, the automotive exhaust gas sensors maiket is stiU predicted to grow to over 100 million sensors per year in the next few years. Furthermore, approximately one half of all NO, emissions into the environment are currently due to power plants and industrial boilers [6]. Although it has been more than two decades since the commercial use of X-sensors began, the deployment of NO electrochanical sensors in combustion control has been lacking. The requirements for NO sensors to be used in a commercial combustion application are summarized in [7, 8], and they are as follows ... 

Typical applications for these high speed IR detectors are characterized by strictly controlled, dark environments where a flash fire could originate. While simple high speed infrared systems have been available for several years, modern sensor and filter developments, coupled with state-of-the-art electronics, have resulted in systems tailored for the munitions industry. These systems are more selective within the electromagnetic spectrum, fast in response, and extremely flexible in application to suppression systems. 

These results are consistent with previous measurements which showed that CO concentration was lowest at the combustor operating conditions that most efficiently reduced the overall emission of toxic gases. Thus a measurement of CO concentration can serve as an effective indicator of combustor performance. The results demonstrate the applicability of multiplexed diode laser sensors for rapid, continuous measurements and control of multiple flowfield parameters, including trace species concentrations, in high-temperature combustion environments. 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

The BioView sensor (DELTA Light Optics, Denmark) was developed especially for industrial applications. It is capable of completely automatic optical measurement for monitoring and control of different bioprocesses. The instrument is conceived to withstand harsh industrial environments (e.g., high temperature, moisture) and electromagnetic interference. For data transfer a single-fiber asynchronous modem is used, which allows a distance between the computer and spectrometer of up to several hundred meters. 

Yet another significant challenge to the successful use of AW sensors is the isolation of their sensitivities to numerous different perturbations, so that only a single, desired interaction is observed. As an example, AW sensors are sensitive to enviixmmental variables such as temperature, pressure, and gas or liquid flow rate in mass-sensing applications, excessive response to these variables can be a serious problem. Controlling the AW sensor environment is the focus of Section 6.4. 

The application of optical immunosensors for environmental monitoring started some years ago. The use of sensors for the measurement of pollutants is a viable alternative in environmental control where it is important to develop sensors of small size, that are reliable, sensitive and selective, for operation in situ and produced by a low cost technology. Several applications have been reported mainly applied to pesticide detection (herbicides, biocides, etc.). The SPR technology has been applied to many environmental problems, mainly for the detection of pollutants in the aquatic environment, such as... 

Flow-based analytical procedures are already used in many fields, e.g., environment, food and health. In tandem with the developments described above, flow analysers will also be used in new and emerging fields of application such as the "omics" (metallomics, genomics and proteomics), biotechnology (enzymatic assays, platforms for bio-sensors and flow immunoassays) and quality-control applications in general. Economic resources will also be a driver for more multi-parametric flow-based methods, particularly with spectrophotometric detection. 

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