Surface acoustic wave devices classes

Piezoelectric-based or acoustic wave (AW) sensors such as surface acoustic wave (SAW), quartz crystal microbalance (QCM) or bulk acoustic wave (BAW), and cantilever-based devices create a specific class of gas sensors widely used in various applications (Ippolito et al. 2009 Korotcenkov 2011) (see Fig. 13.1). Virtually all acoustic wave-based devices use a piezoelectric material to generate the acoustic wave which propagates along the surface in SAW devices or throughout the bulk of the structure in BAW devices. Piezoelectricity involves the ability of certain crystals to couple mechanical strain to electrical polarization and will only occur in crystals that lack a center of inversion symmetry (Ballantine et al. 1996). 

Surface acoustic wave (SAW) devices have been studied in detail for chemical sensing applications (1-12). Nearly all this work has relied on some sort of chemically sensitive interface, many of which, however, are not particularly chemically selective. Table I summarizes the different classes of materials that have been examined for SAW-based chemical sensing applications, with a few examples in each category. Bearing in mind that SAW devices respond to changes in mass/area, none of the materials in Table I can be claimed to be entirely immune to interference fi om nonspecific adsorption, particularly for interferants vrith vapor pressures significantly below ambient pressure. 

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