Gravimetric sensors, acoustic

Acoustic perturbation methods, 14 617 Acoustic streaming, 9 59, 81 Acoustic wave gravimetric technique, acoustic wave sensors and, 22 270. 

See also Gravimetric techniqugges Acoustic waves, sensors using, 22 269-270 Acoustooptic (AO) modulators, 14 676 Acousto-ultrasonics, in nondestructive evaluation, 17 425-426 Acquired Immunodeficiency Syndrome (AIDS), 3 135 25 500. See also Anti-HIV drug candidates HIV entries Nevirapine entries sulfonamide exposure in, 23 506 Acquisitions, 15 639 Acrawax C, dental wax, 8 296 9-Acridinecarbonylimidazole, as... 

Table 10. Comparison of sensitivities and other characteristics of acoustic gravimetric sensors [228], 255], [256) international symbols (short form) have been used to denote specific cuts of the various materials...

Piezoelectricity. The Piezoelectric Ejfect. Because all acoustic gravimetric sensors are based on the phenomenon of piezoelectricity, it seems appropriate to discuss briefly the effect itself. Piezoelectricity was first observed by the Curie brothers (Jaques and Pierre) in 1880 [258]. It is a reversible phenomenon, consisting of linear electromechanical interactions between mechanical and electrical properties in certain crystals (Fig. 52). The effect is generated, as already men-... 

Gravimetric Gardner (UK) Surface acoustic wave (SAW) sensors [20]... 

As the readers may see, quartz crystal resonator (QCR) sensors are out of the content of this chapter because their fundamentals are far from spectrometric aspects. These acoustic devices, especially applied in direct contact to an aqueous liquid, are commonly known as quartz crystal microbalance (QCM) [104] and used to convert a mass ora mass accumulation on the surface of the quartz crystal or, almost equivalent, the thickness or a thickness increase of a foreign layer on the crystal surface, into a frequency shift — a decrease in the ultrasonic frequency — then converted into an electrical signal. This unspecific response can be made selective, even specific, in the case of QCM immunosensors [105]. Despite non-gravimetric contributions have been attributed to the QCR response, such as the effect of single-film viscoelasticity [106], these contributions are also showed by a shift of the fixed US frequency applied to the resonator so, the spectrum of the system under study is never obtained and the methods developed with the help of these devices cannot be considered spectrometric. Recent studies on acoustic properties of living cells on the sub-second timescale have involved both a QCM and an impedance analyser thus susceptance and conductance spectra are obtained by the latter [107]. 

The adsorption and desorption isotherms of an inert gas (classically N2 at 77 K) on an outgassed sample are determined as a function of the relative pressure (Prei = p/Po/ the ratio between the applied pressure and the saturation pressure. The adsorption isotherm is determined by measuring the quantity of gas adsorbed for each value of p/po by a gravimetric or a volumetric method (less accurate but simpler). A surface acoustic wave device can also be used as a mass sensor or microbalance in order to determine the adsorption isotherms of small thin films samples (only 0.2 cm of sample are required in the cell) [42,43]. 

Lucklum and Hauptmann, who have made significant contributions to the development of the theory and applications of the QCM, address the future of this field in a recent review with 235 references [17]. To quote In this review we give an overview of recent developments in resonant sensors including micromachined devices and also list recent activity relating to the (Bio)chemical interface of acoustic sensors. Major results from theoretical analysis of quartz crystal resonators, descriptive for all acoustic microsensors are summarized and non-gravimetric contributions to the sensor signal from viscoelasticity and interfacial effects are discussed. ... 

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