Electrostrictive piezoelectric

Ultrasonication involves the conversion of a conventional 50 / 60 Hz alternating-current line power to 20 kHz electrical energy and transformation to mechanical vibration. A lead zirconate titanate electrostrictive (piezoelectric) crystal, when subjected to alternating voltage, expands and contracts. This transducer vibrates longitudinally and transmits this motion to the horn tip. The horn tip is immersed in the liquid slurry and cavitation... 

Usually, artificial muscle based on electrostrictive, piezoelectric, electrostatic, or ferroelectric materials have been manufactured as a film of the dry polymer, both sides coated with a thin metallic film required to apply the electric field. Electrokinetic artificial muscles [5,6] are constituted by films of polymeric gel (polymer, solvent, and salt) and two electrodes, located as close as possible to the material or coating both on sides, which are required to apply the electric field that drives the electroosmotic process. Any of the actuators described in this paragraph has a triple layer structure metal-electroactive polymer-metal (Figure 16.2). 

The presence of water and ions in electrostrictive, piezoelectric, or ferroelectric polymers produces an overlapping of both actuation processes electromechanical and electrokinetics. The water also generates a problem the high applied-potentials (from several volts to thousand of volts) in an electrolytic media... 

Interface polarization Dipole stretching Ferroelectric hysteresis Electric domain wall resonance Electrostriction Piezoelectricity Nuclear magnetic resonance Ferromagnetic resonance Ferrimagnetic resonance... 

Piezoelectric and Electrostrictive Device Applications. Devices made from ferroelectric materials utilizing their piezoelectric or electrostrictive properties range from gas igniters to ultrasonic cleaners (or welders) (72). 

Multilayer-type piezoelectric or electrostrictive actuators are used for several apphcations including the composite smart stmcture shown in Figure 9... 

Piezoelectrics. AH ceramics display a slight change ia dimension, or strain, under the appHcation of an electric field. When the iaduced strain is proportional to the square of the field iatensity, it is known as the electrostrictive effect, and is expressed by ... 

Due to their high piezoelectric response, electrostriction in ferroelectrics, induced by an applied electric field, can be used as strain-inducing components (just as ferromagnetic materials can be exploited for their magnetostriction). Thus barium... 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

Ferroelectrics Poly(vynidilene fluoride) undergoes electrostriction when subjected to high ac fields, thus can be made into actuators applied pressure produces a piezoelectric response useful in sensors. 

Electrostriction. As distinct from inverse piezoelectric effect, electrostriction is a phenomenon in which the strain and the electrical field inducing the strain are related by Sy = where My are electrostriction coefficients. Several relaxor... 

As will be shown in the theory, the electrostriction effect plays an important role in the piezoelectric effect of polymer films. Moreover, a knowledge of the complex electrostriction constant as a function of frequency reveals a new aspect of the relaxational behavior of polymers. In this review a new method for measuring complex electrostriction constant with varying frequency will be presented with some results for poly(vinylidene fluoride). 

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. 

It must be noted that the above consideration for Case (A) assumes that the material is elastically heterogeneous but homogeneous in its dielectric property. If we assume heterogeneity in the electrostriction constant, CJC changes with strain, keeping //(//2 — ) constant, and hence another possibility of piezoelectricity may be introduced however, we will not take this complication into account in the following. 

III. Methods for Measuring the Piezoelectricity and Electrostriction Constant of Polymer Films 3.1. Measurement of the Piezoelectric Constant... 

Fig. 7. Sketch of the apparatus for measuring inverse piezoelectric effect in polymer films. B vibrating cantilever beam, E electromagnetic exciter, P electromagnetic pick-up, S specimen film, M weight, C oscillator, Vt, V2 and V3 voltmeters, Sw switch, V d.c. bias source for measuring electrostriction effect. Drawn after Kawai (1) (1969) by permission of the Japan Society of Applied Physics...

A) When an alternating voltage (frequency = to) is applied to the film, the film is strained with frequencies to and 2 to. The former is the inverse piezoelectric effect and the latter the electrostriction effect. By measuring the strain amplitude of the 2to component, we can obtain the electrostriction constant (Oshiki and Fukada, 1971). 

Fig. 28. Piezoelectric stress constant obtained from inverse piezoelectric effect and electrostriction constant of drawn and polarized poly(vinylidene fluoride) film plotted against temperature. Draw ratio = 7. Polarized at 90° C under the field of 400 kV/ctn for 3 hours. Frequency of applied voltage = 37.5 Hz. (Oshiki and Fukada, 1971) Broken line represents dielectric constant at 21.5 Hz for roll-drawn poly (vinylidene fluoride) film (Peterlin and Eiweil, 1969)...

The electrostriction effect, beside its effect on the piezoelectricity, gives a new insight onto relaxations in polymers when the electrostriction constant is obtained over a wide frequency range. It provides us with a knowledge of the strain dependence of relaxation time. 

Oshiki,M., Fukada,E. The inverse piezoelectricity and electrostriction in elongated and polarized films erf polyfvinylidene fluoride). Rep. Progr. Polymer Phys. Japan 14, 471 (1971). 

The strain. flies along the axis of the electric field, E, or most often along the axis of the induced polarization, P. The electrostrictive coefficients for the electric field and polarization are M and O. respectively. Electrostriction is a small effect. In contrast to piezoelectric materials, electrostrictive materials... 

Converse piezoelectricity is a specific kind of a more general phenomenon known as electrostriction. Electrostriction is the deformation of a material exposed to an electrical field. Nearly all dielectrics... 

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