Transducers high-contact

Piezoelectric transducers can be of the high contact, two- or one- point contact types. The contact force between the sample and the transducer has been found to affect resonance spectra. Thus, resonant peaks increase with decreasing contact force also, the resonant frequency is dependent on the contact force [8]. Electrical and mechanical cross-talk between... 

It should be noted that many of the former studies on US-based detection were carried out by using piezoelectric transducers in contact with the sample [18,19]. Some, however, used non-contact electromagnetic transducers [20] and eddy current testing [21]. The greatest restrictions of the latter are that they require an electrically conductive sample and highly precise positioning of the transducer near the sample. 

Standard commercial iastmmentation and control devices are used ia fluorine systems. Pressure is measured usiag Bourdon-type gauges or pressure transducers. Stainless steel or Monel constmction is recommended for parts ia contact with fluoriae. Standard thermocouples are used for all fluorine temperature-measuriag equipment, such as the stainless-steel shielded type, iaserted through a threaded compression fitting welded iato the line. For high temperature service, nickel-shielded thermocouples should be used. 

The resolution of potentiometric transducers is dependent upon the construction of the resistance element. In the case of a wire-wound resistance, in order to obtain a high resistance in a small space, the resistance wire is wound on to a mandrel or card which is straight or formed into a circle or helix depending upon the motion of the contact. This limits the resolution of the transducer as the wiper moves from one wire to the next on the mandrel. The best resolution that can be obtained is about 0.01 per cent (see Section 6.10.1). Typical wire-wound potentiometers have strokes of between 0.0025 m and 0.5 m and rotational versions from about 10° of arc to 50 turns. An alternative often employed is the conductive plastic film element. This provides a continuous resistance element and thus, a zero resolution, but such elements suffer from a higher temperature coefficient of resistance. A more recent development is a combination of earlier types in which a conductive plastic coating is sprayed on to a wire-wound resistor. 

When the conducting polymer is used as ion-to-electron transducer in the form of an intermediate layer between the electronic conductor and the ion-selective membrane it does not significantly influence the sensitivity and selectivity of the ISE, but it allows high potential stability [75]. For example, microfabricated solid-state K+-ISEs with polypyrrole as ion-to-electron transducer was found to show even better long-term potential stability than those based on a hydrogel contact [58]. The potential of the polypyrrole-based K+-ISE was slightly more sensitive to the oxygen concentration of the sample in comparison to... 

Fig. 23. Schematic design of a biosensor that can be mounted in situ. The biosensor itself sits in a housing and consists of a biocomponent such as one or more immobilized enzymes or cells on top of and in close contact with a suitable type of transducer. A buffer or diluent stream can help to extend the useful dynamic range of the biosensor. The analyte arrives at the biosensor by passing a suitable membrane which enhances selectivity and protects the biosensor. An additional mechanical shield in the form of a mesh, grid or frit may be necessary to assure mechanical stability in the highly turbulent zone...

ZnO is a wide band gap semiconductor, which is used for various applications. Based on textured ZnO films one can build highly effective piezo field emitters. On the other hand ZnO is a very effective electron-excited phosphor. ZnO films easily withstand electron fluence more than 1 W/cm. ZnO films doped with Al, Ga, or In have a low resistivity of about 10 " Qcm and a high transparency of about 90%. This is sufficient for applications as a front contact in solar cells, liquid crystal displays etc. Dielectric ZnO films have a high electromechanical coupling factor that allow using ZnO in various surface acoustic wave (SAW) devices such as delay lines, delay-line filters, resonators, transducers and SAW convolvers. 

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