Electrostriction Mechanism Research Articles

Enhancing Electrostrictive Actuation via Strong Electrostatic Repulsion among Field-Induced Nanodomains in a Relaxor Ferroelectric Poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) Random Terpolymer

Electrostrictive polymers having a large strain are desirable for actuation, sensing, and energy harvesting in wearable electronics and soft robotics. However, a high electric field (>100 MV/m) is usually required for current electrostrictive polymers. To realize large electrostriction at reduced electric fields, the fundamental electrostriction mechanism needs to be better understood. In response to this need, the structure and electrostrictive properties of relaxor ferroelectric (RFE) poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] random terpolymers films with different thermal annealing histories were studied in this work. First, the semicrystalline structure of the P(VDF-TrFE-CTFE) terpolymer films was studied by combined small-angle X-ray scattering and wide-angle X-ray diffraction analyses. A three-phase model was employed, namely, crystals and oriented and isotropic amorphous fractions (OAF and IAF). The bulky CTFE units generated taut-tie molecules (TTM) in the crystalline lamella, dividing it into many nanosized crystals (∼1.3 nm thick). It is this unique crystalline structure with nanocrystals and mobile TTM/OAF that enabled the RFE behavior for the P(VDF-TrFE)-based terpolymers. Through electrostriction measurements and nonlinear dielectric analysis, an inverse correlation was observed between the ferroelectric nonlinearity and the electrostrictive coefficient under a high poling electric field (>100 MV/m). This suggested that higher electrostriction performance could be achieved by decreasing the ferroelectric nonlinearity of the RFE terpolymer. Indeed, above the Curie temperature, the paraelectric terpolymer films achieved a high electrostrictive performance with the transverse strain being ∼5% at 200 MV/m. This was attributed to the strong electrostatic repulsion among electric field-induced ferroelectric nanodomains. The finding from this work provides a viable way to design new electrostrictive polymers with higher performance at low driving fields.

Initiation of nanosecond-pulsed discharge in water: Electrostriction effect

Underwater nanosecond-pulsed discharges have been widely utilized in numerous industrial applications. The initial stage of nanosecond-pulsed discharge in water contains extremely abundant physical processes, however, it is still difficult to reveal the details of charge transportation and multiplicative process in liquid within several nanoseconds by currently existing experimental diagnostic techniques. Up to now, the initiation mechanism of underwater nanosecond discharge has been still a puzzle. In this paper, we develop a two-dimensional axially symmetric underwater discharge model of pin-to-plane, and numerically investigate the electrostriction process, cavitation process, and ionization process in water, induced by nanosecond-pulsed voltage. The negative pressure in water caused by tensile ponderomotive force is calculated. The creation of nanoscale cavities (so-called nanopores) in liquid due to negative pressure is modeled by classical nucleation theory with modified nucleation energy barrier. When estimating the temporal development of nanopore radius, a varying hydrostatic pressure is considered to restrain the unlimited expansion of nanopores. We estimate the electron generation rate by the product of the generation rate of incident electrons and the number density of nanopores. The simulation results show that cavitation occurs in liquid within several microns from pin electrode due to the electrostriction, which results in the formation of a large number of nanopores. The expansion of nanopore, caused by electrostrictive pressure on nanopore surface, provides a sufficient acceleration distance for electrons. The impact ionization of water molecules can be triggered by energetic electrons, leading the local liquid to be ionized rapidly. The effects of nanopores on rapid electron generation in water are discussed. Once nanopores are formed, the electrons can be generated in the following ways: 1) Field ionization of water molecules on the nanopore wall continuously provides seed electrons; 2) the seed electrons accelerated in nanopores enter into the liquid and collide with water molecules, resulting in the rapid increase of electrons. It can be inferred that the randomly scattered nanopores act as micro-sources of charges that contribute to the continuing ionization of liquid water in cavitation region near pin electrode. Electrostriction mechanism provides a new perspective for understanding the initiation of nanosecond-pulsed discharge in water.

Amplification of the electrostriction mechanism of photoacoustic conversion in layered media

In this work we have performed an analysis of an electrostriction mechanism of optical-to-acoustical energy conversion on the interface of two materials with low optical absorption. We compared this method of conversion with the widely used thermal conversion based on thin metal film. It was shown that the contribution of the electrostriction mechanism is significantly lower in the case of the homogeneous medium. We demonstrated the possibility to amplify the generated acoustic signal by excitation of the guided modes, for which the energy is localized in a thin dielectric layer (of about 200–400 nm in thickness). Due to the high electromagnetic field energy concentration in the structure, local values of intensity increase by more than two orders of magnitude in comparison to the intensity of the incident light, which also allows an increase in the amplitude of the pressure correspondingly. Thus, in this project, we propose the novel layered dielectric structures, in which the electrostriction effect occurs due to the excitation of the guided modes.

Towards an improved understanding of nanosecond-pulse discharge initiation in water: from cavitation to electron multiplication

Underwater nanosecond-pulse discharges have been widely utilized in numerous industrial applications. However, the physical processes before nanosecond discharge ignition are still not well understood. In this paper, we investigate the full processes incorporating cavitation, nanopores expansion and subsequent electron multiplication based on an electrostriction mechanism. We modify the energy barrier of cavitation to avoid the overestimation of nucleation rate at highly negative pressure. A varying hydrostatic pressure instead of a fixed pressure adopted by previous models is considered to restrain the unlimited expansion of nanopores. We estimate the electron generation rate by the product of the generation rate of incident electrons and the number density of nanopores. The simulation results using real experimental conditions are in accordance with the experimental data. It is inferred that the electrostriction can be responsible for the underlying mechanism of underwater nanosecond discharge. This work provides a quantitative solution to calculating electron generation rate in liquid water under fast-pulse voltages (nanosecond or even picosecond), and can be referred in future 2D and 3D modelling.

Electrostrictive Mechanism of Liquid Breakdown in Strongly Nonhomogeneous Field under the Action of Nanosecond Voltage Pulse

Electrostriction mechanism of breakdown in polar liquid caused by high-voltage nanosecond pulse is studied. Nonstationary motion of liquid in the pin-to-plane system exposed to a pulse with peak voltage of 30 kV and 6-ns duration is numerically analyzed. Cavities in which the breakdown can be initiated are formed in the vicinity of the tip electrode. Dimensions of such cavities are estimated, and the conditions for formation are formulated. Profiles of voltage and current pulses are measured for breakdown in water and air. The velocity of breakdown development in air is determined using the time delay of the pulse measured by the shunt of discharge current at several interelectrode distances. The proposed method has limitations in the measurement of breakdown in water due to the effect of displacement current that exceeds the discharge current.

Progress in constitutive theory and stability research of electroactive dielectric elastomers

Dielectric elastomer has special mechanical and electrical performance. It can change its shape or volume under external electric field and can recover the original shape or volume when the electric field is removed. That makes it one of the most promising electroactive polymers for fabricating actuators, sensors, shakers and energy harvesters and have huge application potential in areas such as artificial muscle, intelligent biomimetics, aerospace, mechanics and biology. This paper make a brief review of dielectric elastomer and its applications firs and then focuses on the progress in dielectric elastomer theories, including constitutive theory, electromechanical stability, snap-through stability, giant electrostriction mechanism, allowable area description and failure analysis of dielectric devices. At last, this paper make a outlook on the research of soft dielectric electroactive elastomer.

The Study of Optoacoustic First and Second Sound Waves in Superfluid Helium under the Effect of Gaussian Laser Light Considering Electrostriction Mechanism

The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostriction mechanism. This study considers crystal parts of superfluid helium with a zero absorption coefficient applying electrostriction mechanism. Affecting Gaussian laser light on these crystal parts, a spectrum of cylindrical first and second sound waves and cylindrical slow and rapid waves is obtained. Meanwhile, frequency of waves amplitudes proportionate to time period of laser light is calculated.

Initiation stage of nanosecond breakdown in liquid

In this paper, based on a theoretical model (Shneider and Pekker 2013 Phys. Rev. E 87 043004), it has been shown experimentally that the initial stage of development of a nanosecond breakdown in liquids is associated with the appearance of discontinuities in the liquid (cavitation) under the influence of electrostriction forces. Comparison of experimentally measured area dimensions and its temporal development were found to be in a good agreement with the theoretical calculations. This work is a continuation of the experimental and theoretical works (Dobrynin et al 2013 J. Phys. D: Appl. Phys. 46 105201, Starikovskiy 2013 Plasma Sources Sci. Technol. 22 012001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 162001, Marinov et al 2013 Plasma Sources Sci. Technol. 22 042001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 3555201), initiated by the work in (Shneider et al 2012 IEEE Trans. Dielectr. Electr. Insul. 19 1597–82), in which the electrostriction mechanism of breakdown was proposed.

Electric field induced ultra-high actuation in a bulk carbon nanotube structure

Electric-field induced nonlinear actuation behavior is demonstrated in a bulk nanotube (CNT) structure under ambient conditions. Completely recoverable and non-degradable actuation over several cycles of electric-field is measured in these structures. A symmetric and polarity independent displacement corresponding up to an axial strain of 14% is measured upon application of a low strength electric field of 4.2kV/m in the axial direction. However, a much lower strain of ∼1% is measured in the radial (or, transverse) direction. Furthermore, the electric field induced actuation increases by more than a factor of 2 upon impregnating the CNT cellular structure with copper oxide nano-particles. An electrostriction mechanism, based on the electric-field induced polarization of CNT strands, is proposed to account for the reported actuation behavior.

Electrostrictive Mechanism of Radiation Self-Action in Nanofluids

The electrostriction mechanism of beam self-focusing in nanofluids is theoretically investigated. An analytical solution of the diffusion equation, which describes the dynamics of particles in nanofluids, was obtained and studied. Explicit expressions for the nonlinear part of the refractive index and concentration lens focal length are presented. It is shown that there is a limit on the radiation intensity associated with the physical and hydrodynamic characteristics of the phenomena in these processes.

Manifestation of optical quadratic nonlinearity in gas mixtures

In optical media, particularly in gases, there existseveral types of quadratic optical nonlinearity. Thisphenomenon is manifested in a nonlinear (quadratic)dependence of the refractive index n of the opticalmedium on the light wave amplitude. The best knownis the Kerr optical nonlinearity, for which the increasein the refractive index is associated with orienting mol-ecules in the light wave field. The other example is thephenomenon of electrostriction, in which the light wavecompresses the medium and elevates its density,thereby increasing n [1]. It turns out that, in gas mix-tures, there exists one more mechanism of manifestingoptical nonlinearity. We are implying the fact that themolecules of a gas with the highest n are attracted to theregion of the most intense light. As a result, the refrac-tive index of the mixture is higher compared to theequilibrium mixture in the absence of optical radiation.Thus, quantity n inside the radiation field is dependenton the radiation intensity. In the case of increasing n ,the work spent to separate molecules in a gas mixturecan be smaller than that spent for the same increase in n by means of compression of the same gas mixture bythe electrostriction mechanism. Therefore, the effectobserved can be even stronger than in the case of elec-trostriction.As is well known, the separation of a mixture isassociated with an energy consumption determined bythe expression W = T ∆ S , where T is the temperature ofthe gas mixture and ∆ S is the rise of the entropy whenthe gases are mixed [2]. If this process is adiabatic, theincrement of entropy is zero. Therefore, when the heatinflow to the system under consideration is negligible,the work needed for separation of the gas mixture isclose to zero, and the nonlinearity coefficient of the gasmixture can be rather high. However, the time of occur-ring transition processes accompanied by the suction ofmolecules of a gas with the highest n is also relativelylong, because it is associated with transport phenom-ena. Therefore, in the case of instantaneous appearanceof radiation, e.g., in a gas discharge, there is no domainfrom which molecules can be sucked, since the radia-tion is present in the entire volume of the mixture.However, this does not imply that the effect of the indi-cated mechanism is not manifested.In the same manner as the condensation of saturatedvapor can be accompanied by the appearance of a fogconsisting of small droplets of liquid, the molecules ofa gas with the highest n are concentrated by intenseradiation in a local domain. In contrast to droplets ofliquid—where molecules occupy the entire droplet vol-ume—in a gas mixture, molecules are concentrated in athin spherical layer (TSL) having an increased refrac-tive index. The TSL plays the role of a bent planar lightguide directing the light that circulates in it over all pos-sible paths. Intense light, in turn, provides the concen-tration in the TSL of molecules with the highest n .Thus, in a gas mixture, intense light condenses asthough into light fog consisting of a set of different-sizeTSLs.Figure 1 illustrates the stages of the appearance ofthese formations. We assume that, in a certain domain,a fluctuation of the density and/or of the concentrationhas occurred. In this case, the boundary of the domainwith an elevated refractive index is convex. Then, inaccordance with the eikonal equation, a beam propagat-ing along the tangent to the boundary is bent toward themaximum refractive index. The radius of curvature isdetermined by the expression R

Close Relationship between Bending-Electrostrictive Response and Space Charge Distribution in a Polyurethane Film

The object of our study was to clarify the mechanism of the bending-electrostrictive response of a polyurethane film. We investigated the mechanism using the pulsed electroacoustic method for measuring the space charge distribution in the film. The measurements revealed a similarity between the time courses of the bending-electrostrictive response and the space charge accumulation. That is, the film gradually bent to the cathode side during the first electric-field application to a virgin sample. However, it quickly bent during the succeeding second application. On the other hand, the measurement of the space charge showed that a negative space charge gradually accumulated inside the anode during the first application. However, it quickly accumulated during the second application. Time plots of the bending deformation and the space charge density clearly showed the above similarity in the response profile. Such a similarity suggests that the space charge is closely related to the bending electrostriction mechanism.

Electrostriction mechanism of Bragg grating formation in germanosilicate fibres

An electrostriction model is proposed for the photorefractive effect observed during the writing of Bragg gratings in germanosilicate fibres. Electrostriction is caused by a spatial charge grating formed upon the exposure to UV radiation. According to our estimate, the contribution of electrostriction to the photorefractive effect under real writing conditions is comparable with the contribution from colour centres and exceeds the contribution from the electrooptical effect by more than an order of magnitude. The electrostriction model explains the production of the IIA type Bragg grating in fibres with a high content of germanium in the core, as well as a number of effects that could not be explained earlier.

Transverse Brillouin Effect Produced by Electrostriction in Optical Fibers and Its Impact on Soliton Transmission Systems

Large radial gradient of light intensity in single-mode fibers leads to excitation of transverse acoustic waves through electrostriction mechanism. The nanosecond range for the acoustic effect introduces a time-dependent index evolution for the optical pulses following and results in an additional temporal shift. The dynamic frequency shift of optical pulses in optical fibers is evaluated by a time-domain resolution technique using copropagated pump and probe signals arrangement. Complete electrostrictive response measurements including excitation of pure radial and mixed torsional–radial acoustic modes are presented. In a second time, the acoustic effect is incorporated in the nonlinear Schrödinger equation as a perturbative term. We have investigated the evolution of timing jitter, taking into account both the Gordon–Haus and the acoustic interaction contributions for different dispersion management soliton system configurations in order to evaluate the induced penalties.

Electrostriction mechanism of microwave losses in a ferroelectric film and experimental confirmation

The experimental confirmation of the existence of the electrostriction mechanism of microwave losses in a thin ferroelectric film is discussed. The results of simulation of the dielectric loss tangent due to the mechanism discussed for a planar capacitor with one gap are presented and compared with existing experimental data for an interdigital capacitor. The simulation results agree well with the experimental data. The small discrepancy with experiment could be due to inaccurate determination of the sound velocity in the ferroelectric film and to differences in the capacitor structures used in the simulation and in the experiment.

A perturbation theory and simulations of the dipole solvation thermodynamics: Dipolar hard spheres

Padé truncation of the thermodynamic perturbation theory is used to calculate the solvation chemical potential of a dipolar solute in a model fluid of dipolar hard spheres. Monte Carlo simulations of the solvation thermodynamics are carried out over a wide range of solute and solvent dipoles in order to address the following major issues: (i) testing the performance of the Padé perturbation theory against simulations, (ii) understanding the mechanism of nonlinear solvation, and (iii) elucidating the fundamental limitations of the dielectric continuum picture of dipole solvation. The Padé form of the solvation chemical potential constructed in the paper agrees with the whole body of simulation results within an accuracy of 3%. Internal energy and entropy of solvation are also accurately described by the perturbation treatment. Simulations show a complex nonlinear solvation mechanism in dipolar liquids: At low solvent polarities the solvation nonlinearity is due to orientational saturation that switches to the electrostriction mechanism at higher dipolar strengths of the solvent. We find that the optimum cavity radius of the Onsager reaction-field theory of solvation depends substantially on solvent polarity. A general method of testing the performance of linear solvation theories is proposed. It shows that the fundamental failure of continuum theories consists in their inaccurate description of the internal energy and entropy of solvation.

Time-resolved measurement of dynamic frequency chirp due to electrostriction mechanism in optical fibers

The electrostrictional excitation of acoustic waves by light pulses in optical fibers results in a timing jitter in soliton transmissions which, in turn, imposes a limitation on the transmission rate in long-distance communication systems. In this letter, we report for the first time an experimental investigation of this electrostriction effect by time-domain resolution dynamic frequency shift measurement in a copropagating probe and pulse signal arrangement. The experimental results show a very good agreement with the theoretical model reported by Dianov.

Electrostriction mechanism of soliton interaction in optical fibers

In contrast to the mechanism of interaction determined by the Kerr nolinearity, the electrostrictive interaction between picosecond pulses in optical fibers can occur when the temporal interval between them is much greater than their duration. The width of the interval is determined by the lifetime of the sound wave in the fiber core region, i.e., ~1 nsec. It follows from our calculations that for long propagation distances (L > 1000 km) the relative temporal separation of the interacting pulses can reach hundreds of picoseconds at the temporal interval between them of ~1 nsec.

Theoretical resistance of an ionic crystal to destruction by an electric field

We describe an electrostriction mechanism for destruction of an ionic crystal by an electric field. We present a simple theory that transforms into the well-known Rogowskii theory when there is no electrostatic breakdown. We show that electrostatic breakdown of the crystal lattice is due to separation of nearestneighbor ions with different charges to the point where the electric field exceeds the interionic attractive forces. The theoretical tensile strength of a crystal lattice undergoing electrostriction by an electric field is 15 MV/cm.

Isolas in four-wave mixing optical bistability

Optical bistability based on the cross-interaction of two counterpropagating plane waves in a Kerr-like medium is considered. It is shown that the input-output characteristics of such a system have not only multivalued hysteretic response (which was demonstrated by Winful and Marburger in 1980), but also multiple isolated branches (so called isolas) with nonhysteretic jumps from these branches to the main curve (but not vice versa). The isolas were found both in the case in which the problem can be solved analytically (particularly for electrostriction mechanism of optical nonlinearity) and in the general case of arbitrary light-induced anisotropy.