Bulk acoustic wave devices

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. 

In this review, we discuss the development and appUcation to electrochemical problems of a bulk acoustic wave device, the thickness shear mode (TSM) resonator, whose operation (in the simplest case of a... 

Sigalas M, Kushwaha MS, Economou EN, Kafesaki M, Psarobas IE, Steurer W (2005) Classical vibrational modes in phononic lattices theory and experiment. Z Krisstallogr 220 765-809 Thomas L-A (2011) Porous silicon multilayers for gigahertz bulk acoustic wave devices. PhD thesis, University of Bath... 

Zinc oxide (ZnO) is a cheap but important material with many unique properties and potential applications [123-125]. Firstly, it is a gas/pressure-sensing ceramic and can be used as non-linear varistors and sensors [126]. Secondly, piezoelectric ZnO can find applications in surface and bulk acoustic wave devices [127-129]. Thirdly, it is a semiconducting oxide with a wide band gap of 3.37 eV at room temperature and a large exciton energy of 60 meV,... 

Slip is not always a purely dissipative process, and some energy can be stored at the solid-liquid interface. In the case that storage and dissipation at the interface are independent processes, a two-parameter slip model can be used. This can occur for a surface oscillating in the shear direction. Such a situation involves bulk-mode acoustic wave devices operating in liquid, which is where our interest in hydrodynamic couphng effects stems from. This type of sensor, an example of which is the transverse-shear mode acoustic wave device, the oft-quoted quartz crystal microbalance (QCM), measures changes in acoustic properties, such as resonant frequency and dissipation, in response to perturbations at the surface-liquid interface of the device. 

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

Piezoelectric phenomena are related to the reversible electric polarization generated by mechanical strain in crystals that do not display a centre of S5mimetry. The signal produced by acoustic wave devices is generated by bulk or surface acoustic waves launched by metal transducers at ultrasonic fi-equencies. Such waves are propagated through piezoelectric materials. 

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. 

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. 

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]. 

Rosenbaum J. F., Bulk Acoustic Wave Acoustic Theory and Devices (London Artech House Boston, 1988). 

The goal of this entry is to categorize and describe the mainstream acoustic wave biosensors. We will begin by discussing biosensors that utilize bulk acoustic waves and subsequently analyze devices that employ surface acoustic waves. We will also examine sensors that employ... 

Bulk acoustic wave (BAW) biosensors employ either longitudinal or shear waves, although the latter is often preferred to reduce acoustic radiation in the medium of interest. They are the oldest and the simplest acoustic wave devices. BAW devices consist of a parallel electrode placed on both sides of the thin piece of crystal. BAW sensor can technically employ any piezoelectric element, and typically quartz is used, as it is an inexpensive material readily available in nature and easily synthesizable in abundant quantities. In addition, thin disks of quartz are more stable at high temperatures than other piezoelectric elements. When an alternating electric field is applied, it results in a potential difference... 

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). 

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