Transducers, description

Taxonomy No. 2 18 1 Equipment Description TRANSDUCERS - CURRENT TO PNEUMATIC ... 

To minimize experiment time a very strong Co/Rh source was used, with an initial source strength of about 350 mCi at launch. Instrument internal calibration is accomplished by a second, less intense radioactive source mounted on the end of the velocity transducer opposite to the main source and in transmission measurement geometry with a reference sample. For further details, see the technical description in Sect. 3.3. 

Hair cells are specialized mechanoreceptors located in the inner ear these cells transduce mechanical forces transmitted by sound and head movement, and permit an organism to sense features of the external world. Well-characterized biophysically, a molecular description of hair-cell transduction has finally begun to emerge. 

With the qualitative illustration of observable shock and bubble parameters shown in Fig 5, we can now proceed to a description of the test methods used to obtain such data. Figs 2 5 immediately suggest the use of pressure transducers to follow the pressure-time histories of underwater explns. Similarly Fig 1 (bottom portion) suggests the use of visual (photographic) techniques to obtain dimensions and positions of the gas bubbles. Indeed, these are the major techniques now used in studying underwater shock and bubble effects... 

The apparatus developed for yb measurements of BLM deserves brief comment since it can be used not only to examine the effects of various substances on BLM but is readily adaptable for studying other types of interfacial films and related adsorption phenomena at either air-water or oil-water interfaces (and bifaces). Unlike both the Wil-helmy plate and film balance methods, the present technique measures 7i directly. From the description of the apparatus and procedure that the present method relies on the ability to measure the very small pressure difference across an interface (or biface). For certain BLM s, the pressure heads measured are only fractions of a millimeter of water. Therefore, the method described here has been possible only as a result of developing pressure transducers of high sensitivity. 

G. Bourdon Gauges. As an alternative to mercury manometers there is a variety of gauges based on mechanical or electrical pressure transducers. This section presents a description of purely mechanical gauges which still find use in this electronic age.4 The metal Bourdon gauge (Fig. 7.5) is fashioned around a semicircular thin-walled metal tube with mechanical linkage to a pointer. Fused-quartz spiral gauges are also available. In this case, a thin spiral is sensitive to a pressure differential, and the deflection is balanced with air pressure in the surrounding envelope. The air pressure is then measured with a manometer. 

Various types of pressure transducers with digital readout are available with metal interior construction. These have become quite popular for fluorine-handling systems and the like. A description of some of the common types is given in Chapter 7. 

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. 

The description of an interface acting as a transducer from ionic to electronic conduction is due to Eliezer Gileadi. 

Fig. 1 Schematic description of the fretting device. (1) spherical glass counterface, (2) epoxy specimen, (3) tangential load transducer, (4,5) normal load transducers, (6) extensometer, (7) microscope and CCD camera.

An excellent overview and in-depth description of miniaturization techniques is given in Ref. [2]. Here, only a few examples of how miniaturized biosensors can he fabricated are described. A clear distinction can be made between the miniaturization of the biosensor fluid flow system and the use of a miniaturized transducer. Both result in different advantages for the biosensor assay, as it will be discussed below. In the case of biosensor fluid flow system, microfabrication tools used are by far fewer than those applied to the fabrication of micro/nanotransducers, which can span all of the micro/ nanofabiication techniques developed. 

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