Piezoelectric effect mechanisms

The pyroelectric effect is similar to the piezoelectric effect. Mechanical deformations generate electric voltages. Such deformations are caused by temperature changes with pyroelectric materials. 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

In general terms, the pyroelectric coefficient of a free sample consists of three components. The first, called the real coefficient, depends on the derivative of spontaneous polarization with respect to the temperature. The second is derived from the temperature dilatation and can be calculated based on mechanical parameters. The third coefficient is related to the piezoelectric effect and results from the temperature gradient that exists along the polar axis of the ciystal. 

These two anciently served as a means of ignition. They still can. Although the sparking of flint and steel is strictly a mechanical phenomenon, any subsequent fires will not be. Other forms of silica still serve as igniters to this day, via the piezoelectric effect. 

The voltage from the battery induces a minute mechanical strain in the crystal, causing it to vibrate - a property known as the piezoelectric effect. 

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... 

Piezoelectric microbalance The piezoelectric microbalance is a resonant frequency device. The piezoelectric effect is the development of a charge on some crystals such as quartz when a stress is applied the stress may be mechanical (e.g., added weight) or electrical. Such crystals may be used as part of a resonance circuit to provide very stable, narrow-band frequencies the quartz crystal is plated on two sides with a thin conducting layer and leads are connected to the resonance circuit so the crystal replaces an LC network. The obtained frequency of vibration (pu) depends on a number of parameters of the crystal but is usually 5-10 MHz. However, if a mass (Am) becomes attached to one side of the crystal, it changes the resonant frequency by an amount At , such that... 

Figure 6.28 Schematic illustration of the piezoelectric effect that occurs in (a) an unstressed and (b) stressed piezoelectric material. Mechanical deformation can also occur when (c) a voltage is applied to a piezoelectric material. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission John Wiley Sons, Inc.

Ferroelectrics. Among the 32 crystal classes, 11 possess a centre of symmetry and are centrosymmetric and therefore do not possess polar properties. Of the 21 noncentrosymmetric classes, 20 of them exhibit electric polarity when subjected to a stress and are called piezoelectric one of the noncentrosymmetric classes (cubic 432) has other symmetry elements which combine to exclude piezoelectric character. Piezoelectric crystals obey a linear relationship P,- = gijFj between polarization P and force F, where is the piezoelectric coefficient. An inverse piezoelectric effect leads to mechanical deformation or strain under the influence of an electric field. Ten of the 20 piezoelectric classes possess a unique polar axis. In nonconducting crystals, a change in polarization can be observed by a change in temperature, and they are referred to as pyroelectric crystals. If the polarity of a pyroelectric crystal can be reversed by the application on an electric field, we call such a crystal a ferroelectric. A knowledge of the crystal class is therefore sufficient to establish the piezoelectric or the pyroelectric nature of a solid, but reversible polarization is a necessary condition for ferroelectricity. While all ferroelectric materials are also piezoelectric, the converse is not true for example, quartz is piezoelectric, but not ferroelectric. 

In the usual experiment where E0 = 0, the term kSE in Eq. (9) does not make any contribution as far as the electrical response with the same frequency as the mechanical excitation is concerned. However, as will be described in 2.2 and 2.4, the piezoelectric constant of a polymer film is sometimes a function of the electrostriction constant which plays an important role in the anisotropy and relaxational behavior of the piezoelectric effect. 

The piezoelectric effect has been shown to exhibit a relaxational nature and the complex piezoeletric constant is a function of frequency and temperature. In Group (A), the relaxation is ascribed to either the nature of the crystallite itself or the viscoelasticity of the amorphous phase in which the crystallites are embedded. In the former case, the piezoelectric relaxation is a cross-coupling phenomenon of dielectric relaxation and mechanical relaxation of the crystallite. In the latter, on the other hand, the relaxation is governed by the mechanical relaxation of the amorphous phase. 

PIEZOELECTRIC EFFECT. The interaction of mechanical and electrical stress-strain variables in a medium. Thus, compression of a crystal of quartz or Rochelle salt generates an electrostatic voltage across it, and conversely, application of an electric field may cause the ciystal to expand or contract in certain directions, Piezoelectricity is only possible in crystal classes which do not possess a center of symmetry. Unlike clcctrostricdon, the effect is lineal in the field strength. 

Piezoelectric materials are materials that exhibit a linear relationship between electric and mechanical variables. The direct piezoelectric effect can be described as the ability of materials to convert mechanical stress into an electric field and the reverse, to convert an electric field into a mechanical stress. The use of the piezoelectric effect in sensors is based upon the latter property. 

Piezoelectric materials are materials that exhibit a linear relationship between electric and mechanical variables. Electric polarization is proportional to mechanical stress. The direct piezoelectric effect can be described as the ability of materials to convert mechanical stress into an electric field, and the reverse, to convert an electric field into a mechanical stress. The use of the piezoelectric effect in sensors is based on the latter property. For materials to exhibit the piezoelectric effect, the materials must be anisotropic and electrically poled ie, there must be a spontaneous electric field maintained in a particular direction throughout the material. A key feature of a piezoelectric material involves this spontaneous electric field and its disappearance above the Curie point. Only solids without a center of symmetry show this piezoelectric effect, a third-rank tensor property (14,15). 

The piezoelectric effect is an electromechanical effect in which mechanical evoke and reverse an electric reaction in a ferroelectric material and vice versa. The word piezo has been derived from the Greek piezein which means press . Compounds are composed of positive and negative ions and are electrically neutral as a whole. The fact that electrically charged particles are still present in the crystal can for example be demonstrated by means of the electric... 

The simplest SAW sensor is a two-terminal transmission (delay) line in which the acoustic (mechanical) wave is piezoelectrically launched in one oscillator, called the transmitter. It travels along the surface of the substrate and is then transformed back into an electrical signal by the reverse piezoelectric effect at the receiving oscillator (Fig. 4.18). 

Today, the atomic mechanism that causes the piezoelectric effect is well understood. Quartz, for example, consists of long chains of silicate (Si042-) groups arranged in a helical pattern, as shown in the diagram below. In any one silicate group, the atoms are arranged... 

The piezoelectric effect entails a linear coupling between electrical and mechanical energies. Numerous piezoelectric coefficients are in use, depending on the electrical and mechanical boundary conditions imposed on the part under test. Each of the piezoelectric d, e, g, and h coefficients can be defined in terms of a direct and a converse effect the two sets of coefficients are related by thermodynamics. For example, the piezoelectric charge coefficient, dkjk, can be defined via [1] ... 

The term piezoelectric nonlinearity is used here to describe relationship between mechanical and electrical fields (charge density D vs. stress a, strain x vs. electric field E) in which the proportionality constant d, is dependent on the driving field, Figure 13.1. Thus, for the direct piezoelectric effect one may write D = d(a)a and for the converse effect x = d(E)E. Similar relationships may be defined for other piezoelectric coefficients (g, h, and e) and combination of electro-mechanical variables. The piezoelectric nonlinearity is usually accompanied by the electro-mechanical (D vs. a or x vs. E) hysteresis, as shown in Figure 13.2. By hysteresis we shall simply mean, in the first approximation, that there is a phase lag between the driving field and the response. This phase lag may be accompanied by complex nonlinear processes leading to a more general definition of the hysteresis [2],... 

The discovery of the piezoelectric effect (the appearance of electrical charges on different surfaces of crystals under mechanical stress) in 1880 by Pierre Curie (1859-1906) and his brother Jacques (1855-1941) is discussed in a brief paper.91... 

In practice the energy transfer electrical-to-mechanical (or vice versa) occurs in a complex 3-dimensional way. The strains caused by applied electrical or mechanical stresses have components in three orthogonal directions necessitating the description of the piezoelectric effect in terms of tensors, as outlined below. 

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