Other Transducers

Recent advances in instrumentation range from novel (laser) sources and highly compact spectrometers over waveguide technology to sensitive detectors and detector arrays. This, in combination with the progress in electronics, computer technology and chemometrics, makes it possible to realise compact, robust vibrational spectroscopic sensor devices that are capable of reliable real-world operation. A point that also has to be taken into account, at least when aiming at commercialisation, is the price. Vibrational spectroscopic systems are usually more expensive than most other transducers. Hence, it depends very much on the application whether it makes sense to implement IR or Raman sensors or if less powerful but cheaper alternatives could be used. 

In practice, surface modifications are restricted to sensors of the ATR- or FEWS-type. For other transducer layouts, the sample - radiation interaction is less localised, making a modification difficult to impossible. Depending on the analytes and the environment of the sensor, two basic surface modification strategies can be used to enhance the function of vibrational spectroscopic optical chemical sensors. The functional layers can either be... 

A shadow-mask technique has been applied for the local metal deposition to exclude metal residues on other designs processed on the same wafer (Fig. 4.2b). Such metal residues may be caused by imperfections in the patterned resist due to topographical features on the processed CMOS wafers or dust particles. The metal film is only deposited in those areas on the wafer, where it is needed for electrode coverage on the microhotplates. This also renders the lift-off process easier since no closed metal film is formed on the wafer, so that the acetone has a large surface to attack the photoresist. Another advantage of the local metal lift-off process is its full compatibility with the fabrication sequence of chemical sensors based on other transducer principles [20]. 

Table 1. Microbial species used for BOD-sensors based on amperometric oxygen determination and their parameters (it is noted when other transducer are used)... 

In general, one should be aware that tablet press instrumentation involves the use of strain gauges or piezoelectric transducers to provide a voltage signal proportional to the force applied for the compaction operation. Let us say we can measure forces, such as those applied to the granulation by the punches, that applied to the die wall, that required for tablet ejection, etc. With tlie use of other transducers we can also measure distance. With the measurement of force and distance, we can calculate work, energy, etc. 

Other Transducers. Ultrasound also has been used for the measurement of force, vibration, acceleration, interface location, position changes, differentiation between the composition of differing materials, grain size in metals, and evaluation of stress and strain and elasticity in materials. Sonic devices can used to detect gas leaks, and to count discrete parts by means of an interrupted sound beam. Frequently, an ultrasonic device can be applied where photoelectric derices are used. Particularly tn situations where light-sensitive materials are being processed (hence presence of light must be avoided), ultrasonic devices may be the detectors of choice. 

Although electrode is used by most researchers, other transducers including non-glass electrode also have been investigated. Thermistor is... 

There is a continuing demand for the application of electrochemical sensors with a good quality/cost performance not only in comparison to sensors based on other transducer mechanisms but also to some standard analytical methods. Electrochemical Sensor Analysis (ECSA) presents novel theoretical considerations along with detailed applications of electrochemical (bio)sensors. The combination of both theoretical and practical aspects provides a comprehensive forum that integrates interdisciplinary research and development, presenting the most recent advances in applications in various important areas related to everyday life. Additionally ECSA reflects that electrochemical sensor analysis is already a well established research and applied area of analytical chemistry. 

Chemical sensors utilize the immunological recognition principle by coupling with optical, electrochemical, or other transducer (signal transfer) described e.g. by Eggins (1996) and Rogers et al. (1998). A tendency to miniaturized formats ( chips ) as part of the nanotechnology can be observed. 

In hemodialysis devices, urea analysis makes it possible to monitor the effect of the medical treatment continuously. For this purpose, the ET feasibility in urea monitoring was investigated. In comparison to other transducers, the ET... 

When compared with other transducer technologies, piezoelectric sensors have several specific features ... 

Beynnon uses a differential voltage reluctance transducer, DVRT, produced by Micro Strain, Burlington, VT, to measure ligament strain. The DVRT is a form of LVDT which was described above. The miniature DVRT displacement transducer allows access to delicate and hard-to-reach structures. It is much smaller than other transducers and measures only 1.5 mm in diameter. The... 

However, all these sensors suffer from the very slow kinetics of the dissociation of the complexes. Thus renewal of the transducer surface for repeated measurements with the same device is very difficult. Dissociation of the complexes can be attained by applying highly concentrated urea solutions to the sensor, but even then not more than a few measurements are possible with the same device, as has been shown with a sensor for Salmonella typhimurium [236]. As a consequence, the application of immunological reactions for these and other transducer surfaces is in general limited to one-shot measurements. On the other hand, as antibodies can be obtained against nearly any substance, affinity sensors, mainly those based on piezoelectric crystals, offer so many possibilities that their further development is a promising challenge. 

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