Bulk Acoustic Waves

Alternatively the capillary rise can be measured using a bulk acoustic wave sensor [97Che]. (Data obtained with these methods are labelled BAW). 

A schematic diagram of a bulk acoustic wave (BAW) chemical sensor is composed of a BAW piezoelectric resonator with one or both surfaces covered by a membrane (CIM) (fig. 14). 

There is increasing interest in the use of specific sensor or biosensor detection systems with the FIA technique (Galensa, 1998). Tsafack et al. (2000) described an electrochemiluminescence-based fibre optic biosensor for choline with flow-injection analysis and Su et al. (1998) reported a flow-injection determination of sulphite in wines and fruit juices using a bulk acoustic wave impedance sensor coupled to a membrane separation technique. Prodromidis et al. (1997) also coupled a biosensor with an FIA system for analysis of citric acid in juices, fruits and sports beverages and Okawa et al. (1998) reported a procedure for the simultaneous determination of ascorbic acid and glucose in soft drinks with an electrochemical filter/biosensor FIA system. 

Tan YG, Peng H, Liang CD, Yao SZ. A new assay system for phenacetin using biomimic bulk acoustic wave sensor with a molecularly imprinted polymer coating. Sens AcUiat B 2001 73 179-184. 

MOS metal oxide sensor, MOSFET metal oxide semiconductor field-effect transistor, IR infrared, CP conducting polymer, QMS quartz crystal microbalance, IMS ion mobility spectrometry, BAW bulk acoustic wave, MS mass spectrometry, SAW siuface acoustic wave, REMPI-TOFMS resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry... 

First, the underlying principles upon which bulk acoustic wave (BAW) devices operate are described. When a voltage is applied to a piezoelectric crystal, several fundamental wave modes are obtained, namely, longitudinal, lateral and torsional, as well as various harmonics. Depending on the way in which the crystal is cut, one of these principal modes will predominate. In practice, the high-frequency thickness shear mode is often chosen since it is the most sensitive to mass changes. Figure 3.4 schematically illustrates the structure of a bulk acoustic wave device, i.e. the quartz crystal microbalance. 

Rosenbaum, J. F. Bulk Acoustic Wave Theory and Devices, Artech Boston, Sect. 

Quartz crystal microbalance (QCM) Surface plasmon resonance (SPR) Piezoelectric quartz crystal (PQC) Bulk acoustic wave (BAW) surface acoustic wave (SAW) 4-vinylpyridine (4-VP) Ethylene glycol dimethacrylate (EDMA) Methacrylic acid (MAA), Ethylene glycol dimethacrylate (EDMA) IV-phenylacrylamide (PAM) Diethylamino ethyl methacrylate (DEAEM). 

Surface acoustic waves (SAW), which are sensitive to surface changes, are especially sensitive to mass loading and theoretically orders of magnitude more sensitive than bulk acoustic waves [43]. Adsorption of gas onto the device surface causes a perturbation in the propagation velocity of the surface acoustic wave, this effect can be used to observe very small changes in mass density of 10 g/cm (the film has to be deposited on a piezoelectric substrate). SAW device can be useful as sensors for vapour or solution species and as monitors for thin film properties such as diffusivity. They can be used for example as a mass sensor or microbalance to determine the adsorption isotherms of small thin film samples (only 0.2 cm of sample are required in the cell) [42]. 

The most used devices in biosensors are generally bulk acoustic wave (BAW)-based employing AT-cut quartz crystals. 

Mannelli, I., Minunni, M., Tombelli, S., Mascini, M. (2003). Bulk acoustic wave (BAW) affinity biosensor for genetically modified organisms (GMOs) detection. IEEE Sens. J. 3,369-375... 

Rosenbaum JF (1988) Bulk acoustic wave theory and devices. Artech, Boston... 

Although this chapter is concerned with bulk acoustic wave (BAW) devices, some of the concepts apply to shear horizontal surface acoustic wave (SH-SAW) devices in a similar way [33,34]. When modeling SH-SAW devices, one usually decomposes the wave vector into a vertical and a lateral component. The vertical component obeys similar laws as the shear wave in a BAW resonator. This being said, we confine the discussion to BAW devices (also termed thickness-shear resonators) in the following. 

Fig. 8 Idealised model of acoustic attenuation. A Diagrammatic representation of a thickness shear mode bulk acoustic wave resonator, coated with a rigid metal adhesion and electrode layer, a rigid chemical linker layer, a finite viscoelastic antibody receptor layer, a second adherent finite viscoelastic analyte layer, and finally a Newtonian liquid. B An idealised model of acoustic attenuation from bulk quartz through the above layers of varying viscosity, density, and shear modulus...

The most commonly known oscillator sensors are bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices. The BAW devices operate according to the Sauerbrey principle that very thin films on AT-cut crystals can be treated as equivalent mass changes of the crystal. The SAW devices can operate either on the Rayleigh wave propagation principle at solid thin-film boundaries [3] or as bulk wave devices [4]. 

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