Piezoelectric material device

The basis for the present-day generation of ultrasound was established as far back as 1880 with the discovery of the piezoelectric effect by the Curies [1-3]. Most modern ultrasonic devices rely on transducers (energy converters) which are composed of piezoelectric material. Such materials respond to the application of an electrical potential across opposite faces with a small change in dimension. This is the inverse of the piezoelectric effect and will be dealt with in detail later (Chapter 7). If the potential is alternated at high frequencies the crystal converts the electrical energy to mechanical... 

Nylon 11 (Equation 6.56) is also a piezoelectric material that can be aligned when placed in a strong electromagnetic field giving films used in infrared-sensitive cameras, underwater detection devices, and in electronic devices since it can be overlaid with printed circuits. 

Closely related to ferroelectricity is piezoelectricity in which polarization is induced and an electric field is established across a specimen by the application of external force (see Figure 6.28a,b). Reversing the direction of the external force, as from tension to compression, reverses the direction of the field. Alternatively, the application of an external electric field alters the net dipole length and causes a dimensional change, as in Figure 6.28c. Piezoelectric materials can be used as transducers—devices that... 

Piezoelectric materials are used in many different types of sensing—actuating devices. A few applications include printing, monitoring of performance behavior of adhesive joints, and intelligent processing. 

In the devices discussed above, the acoustic wave propagates in a slab of piezoelectric material whose thickness is infinitely larger than the wavelength of the propagating wave (Table 4.2). When the thickness of the plate is reduced so that it becomes comparable to A, the whole plate becomes involved in the periodic motion and a symmetric and antisymmetric Lamb wave is created (White et al., 1987 Fig. 4.21). 

When it is struck or pressed, quartz generates an electric current. Materials having this property are known as piezoelectric materials. If an external voltage is applied across the crystal, the crystal undergoes vibrations that are in resonance with the alternating current frequency. This type of behavior is the basis for quartz being used as a timing device in watches or in crystals used to establish radio frequencies. 

Sensitive, selective detection of biochemically active compounds can be achieved by employing antigen-antibody, enzyme-substrate, and other receptor-protein pairs, several of which have been utilized in the development of piezoelectric immunoassay devices. The potential analytical uses of these materials has been reviewed, particularly with respect to the development of biochemical sensors [221-224], The receptor protein (e.g., enzyme, antibody) can be immobilized directly on the sensor surface, or it can be suspended in a suitable film or membrane. An example of the sensitivity and response range that can be... 

An example of a one-port device is the bulk resonator shown in Figure 6.1, which has a single, planar electrode on each side of a slab of piezoelectric material (these two electrodes together comprise a single port). Most often, the material takes the form of a disk and the electrodes are circular, covering less than the entire surface of the disk. Connection to an external circuit is typically made via a coaxial cable, with one of the two electrodes connected to the shield and the other to the center conductor. This device is known as a resonator because an external circuit (see Section 6.3.3.2) excites the piezoelectric substrate in such a way that a standing wave is set up in the crystal, which thus resonates. 

With the aid of a particular class of materials (thin-film piezoelectrics), incorporation of AW devices and conventional integrated circuit components on the same silicon substrate is in fact possible. Under the proper conditions, a number of piezoelectric materials can be deposited in thin-film form, typically by RF sputtering, and retain their piezoelectric nature. For this to occur, the crystallites that grow during deposition must be predominantly oriented in a single, piezo-electrically active crystallographic direction. Two such materials are 2 0 and AIN the former has been used as an overlayer on Si wafers to fabricate all of the FPW devices studied for sensor applications to date, and also for SAW resonators. Because extremely thin piezoelectric films are readily fabricated, both ZnO and AIN have been used to make bulk resonators that operate at much higher... 

Trolier-McKinstry, S., Sabolsky, E., Kwon, S., Duran, C., Yoshimura, T., Park, J.-H., Zhang, Z., and Messing, G.L., in Piezoelectric Materials and Devices, Nava Setter, Ed., Ceramic Laboratory, EPFL, Lausanne, Switzerland, 2002. 

The field of molecular electronics may be considered to encompass much more than molecular electronic devices. In its broadest context, molecular electronics may be regarded as simply the application of molecules, primarily organic molecules, to electronics. This definition would include such areas as liquid crystalline materials, piezoelectric materials such as poly(vinylidine fluoride), chemically sensitive field-eflFect transistors (CHEMFET), and the whole range of electroactive polymers. These applications are beyond the scope of this book and are covered in other reviews 34, 33). However, given the basic tenet of molecular electronics, namely, the ability to engineer and assemble molecular structures into a useful device, the broader definition raises the question of whether organic molecules can be specifically assembled or engineered for unique applications in electronics. 

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. 

These companies can supply piezoelectric material and devices such as tubes, stacked assemblies, unimorphs, and bimorphs. 

The main types of SiOj used in indu.siry are high-purity a-quanz, vimeous silica, silica gel. fumed silica and diaiomaceous eanh. The most important application of quartz is as a piezoelectric material (p. 58) it is used in crystal oscillators and filters for frequency control and modulation, and in electromechanical devices such as transducers and pickups tens of millions of such devices are made each year. There is insufficient natural quartz of adequate purity so it must be synthesized by hydrothermal growth of a s crystal using dilute aqueous NaOH and vitreous SiOy at 4(I0°C and... 

The performance of oscillators depends essentially on the stabihty of the acoustic device [7-9] no matter if working as electromechanical resonator or delay line. Because of its extraordinary importance we will concentrate further on resonators, namely quartz crystal resonators. However, the analysis is descriptive also for other piezoelectric materials and partly for delay line elements as well. 

Any type of acoustic transducer, such as quartz crystal microbalance (QCM) or surface acoustic wave device (SAW), is fundamentally based on the piezoelectric effect. This was first described in 1880 by Jacques and Pierre Curie as a property of crystalline materials that do not have an inversion centre. When such a material is subjected to physical stress, a measurable voltage occurs on the crystal surfaces. Naturally, the opposite effect can also be observed, i.e. applying an electrical charge on a piezoelectric material leads to mechanical distortion, the so-called inverse piezo effect. These phenomena can be used to transfrom an electrical signal to a mechanical one and back, which actually happens in QCM and SAW. Different materials are ap-pHed for device fabrication, such as quartz, Hthium tantalate, lithium titanate... 

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