Stability of Non-axisymmetric Electrolyte Jet in High-frequency AC Electric Field

In the present work linear instability of capillary non-axisymmetric micro-jets of electrolyte solutions in a high-frequency alternating axial electric field is investigated theoretically. The gravity affects are neglected. The problem is described by strongly coupled nonlinear system of PDEs for ion transport, electrical field and fluid flow. Viscous liquid is taken. The problem can be divided into outer and inner ones. Solution for the unsteady double ion layer is obtained in Debye-Huckel approximation provided that the oscillation frequency is sufficiently high while Pecklet number based on the Debye layer thickness is sufficiently small. The unsteady double ion layer produces additional normal and tangential stresses on the liquid–gas interface; the latter can either stabilize or destabilize the flow. It is shown that only axisymmetric mode is unstable while non-axisymmetric perturbations are always stable. It is also shown that in unstable case there is an essential dependence of the main stability characteristics on the parameter proportional to the frequency of external field. There are two threshold values of the parameter at which a bifurcation of stability parameters occurs. In particular, the size of the formed drops suffers a jump at increase of amplitude of fluctuation of an electric field. The problem is solved in a broad region of its parameters. There is a qualitative agreement of the theory developed with the available experimental data.     

Electroosmotic fluid motion and late-time solute transport for large zeta potentials

Analytical and numerical methods are employed to determine the electric potential, fluid velocity, and late-time solute distribution for electroosmotic flow in a tube and channel at zeta potentials that are not necessarily small. The electric potential and fluid velocity are in general obtained by numerical means. In addition, new analytical solutions are presented for the velocity in a tube and channel in the extremes of large and small Debye layer thickness. The electroosmotic fluid velocity is used to analyze late-time transport of a neutral nonreacting solute. Zero- and first-order solutions describing axial variation of the solute concentration are determined analytically. The resulting expressions contain eigenvalues representing the dispersion and skewness of the axial concentration profiles. These eigenvalues and the functions describing transverse variation of the concentration field are determined numerically using a shooting technique. Results are presented for both tube and channel geometries over a wide range of the normalized Debye layer thickness and zeta potential. Simple analytical approximations to the eigenvalues are also provided for the limiting cases of large and small values of the Debye layer thickness.     

The Local Electric Field in Photorefractive and Other Semi-insulating Materials

Abstract

Debye-Huckel theory is applied to determine the local electric field around a dipole in a photorefractive semi-insulating material. The dipole can be either induced, as in the presence of an electric field, or permanent. It is shown that when the Debye screening length is large, the local electric field E is given by E_M(? + 2)/3, where E _M is the macroscopic electric field. On the other hand, when the Debye screening length is small, the local electric field is equal to the macroscopic electric field.     

A mechanism of the Fréedericksz surface dynamic effect

It is shown that the period of low-frequency relaxation processes involved in the local reorientation of molecules in a plane-oriented nematic liquid crystal is determined both by relaxation of a weakly deformed director upon switching off the applied field and by redistribution of the voltage drop between the bulk and the near-electrode region (electric double layer). The maximum deformation of the director takes place in the surface layer with a thickness equal to the Debye screening length.     

Anti‐plane mechanical and in‐plane electrical fields for a finite electrode/punch on a finite piezoelectric layer

The problems of a surface electrode and a rigid punch on a finite piezoelectric layer are considered in this paper. The resultant force and the accumulated electric charge on the electrode/punch are prescribed. Closed‐form solutions for the electromechanical fields at the electrode/punch tip are obtained and are expressed in terms of the applied strain and electric field intensity factors. For infinite layer thickness, the strain and electric field intensity factors are obtained in closed‐form. For finite layer thickness, the strain and electric field intensity factors are obtained numerically by the singular integral equation technique. The effect of layer thickness on the electrode/punch tip fields is discussed. It is found that the field intensities at the electrode/punch tip can be reduced considerably by decreasing layer thickness. In addition to the single electrode/punch problem, this paper also provides a solution technique for two collinear surface electrodes/punches on a finite piezoelectric layer. The effect of the relative distance between the two electrodes/punches on the electromechanical fields in the piezoelectric layer is also discussed.     

A piezoelectric screw dislocation interacting with a nonuniformly coated circular inclusion

This paper investigated the interaction of a piezoelectric screw dislocation with a nonuniformly coated circular inclusion in an unbounded piezoelectric matrix subjected to remote antiplane shear and electric fields. In addition to having a discontinuous displacement and a discontinuous electric potential across the slip plane, the dislocation is subjected to a line force and a line charge at the core. The alternating technique in conjunction with the method of analytical continuation is applied to derive the general solutions in an explicit series form. This approach has a clear advantage in deriving the solution to the heterogeneous problem in terms of the solution for the corresponding homogeneous problem. The presented series solutions have rapid convergence which is guaranteed numerically. The image force acting on the piezoelectric screw dislocation is calculated by using the generalized Peach–Koehler formula. The numerical results show that the varying thickness of the interphase layer will exert a significant influence on the shear stress and electric field within the circular inclusion, and on the direction and magnitude of the image force. This solution can be used as Green’s function for the analysis of the corresponding piezoelectric matrix cracking problem.     

Acousto-electric attenuation in a layered structure analyzed by the transmission line technique

In general, theoretical determination of attenuation of ultrasonic waves caused by acousto-electric interaction in any structure is cumbersome and difficult. However, by adopting a transmission line model and using the technique of capacitance perturbation, the analytical process can be greatly simplified. In this paper, we start to analyze a simple structure of an infinitesimally thin semiconductor film deposited on a SAW substrate without an isolation layer in-between. Results for a simplified case are obtained. This analysis is then extended to the general layer structure for both an arbitrary thickness semiconductor layer and an isolation layer. The device parameters are chosen such that the charge relaxation time is much smaller than the duration of the wavelength. Therefore, the electric potential accompanying the acoustic wave is thoroughly screened. Thus, the induced electric field beyond a Debye length or at the top of the semiconductor is negligible. Under this condition, the induced potential as well as the space charge density waves possess a simple form. By integrating the space charge across the thickness of the semiconductor, an effective surface charge density is obtained. With the surface charge density known, one can readily calculate the value of the perturbed capacitance and determine the attenuation constant. The results are in agreement with other analyses.     

Light distribution close to focus in biaxially birefringent media

The effect of focusing into a biaxially birefringent medium on the light distribution in the focal region of a high-NA optical system is investigated with the Debye approach to vectorial diffraction theory. Attention is limited to media with small birefringence. The electric field in the focal region is the sum of the field of the two polarization eigenmodes of the biaxially birefringent medium. Both modes are generally astigmatically aberrated, are defocused with respect to each other, and have a polarization field that is nonuniform over the pupil. The diffraction integrals are calculated numerically on the basis of an expansion of the field close to focus in terms of partial waves.     

THE EFFECTIVE DIELECTRIC CONSTANT OF DUST LAYERS

The electrical breakdown of a dust layer usually occurs at average electric fields which appear to be too small to initiate the breakdown. This suggests that the local electric field where breakdown occurs is somehow enhanced over that of the average field across the layer. AC dielectric measurements performed on the dust layer can be used to determine an effective static dielectric constant at a given temperature. The use of this dielectric constant in an expression for the local electric field, which combines the effects of dielectric polarization and space charge in the layer, results in predicted values of the local electric field which can be more than an order of magnitude larger than the applied field. In studies involving 11 different dust species, the dielectric constant was found to depend on temperature and layer thickness, as well as the concentration of alkali and alkaline earth metals in the dust.     

The effect of an alternating electric field on the liquid dielectric convection in a horizontal capacitor

The electroconvective instability in a low conducting nonuniformly heated liquid occurring in an alternating electric field between plates of a horizontal plane capacitor was studied in terms of the equations of electrohydrodynamics for arbitrary field modulation frequencies and various shapes (harmonic and triangular). In the gravitational field, the instability is determined by the interplay of dielectrophoretic and thermogravitational mechanisms. The layer heated from above can feature the parametric instability. In the low-frequency range, a numerical solution to the problem obtained by the Floquet method well agrees with the asymptotic results.     

Fracture analysis of a piezoelectric layer with a penny-shaped and energetically consistent crack

The problem of an eccentric penny-shaped crack embedded in a piezoelectric layer is addressed by using the energetically consistent boundary conditions. The Hankel transform technique is applied to solve the boundary-value problem. Then two coupling Fredholm integral equations are derived and solved by using the composite Simpson’s rule. The intensity factors of stress, electric displacement, crack opening displacement and electric potential together with the energy release rate are further given. The effects of the thickness of a piezoelectric layer and the discharge field inside the penny-shaped crack on the fracture parameters of concern are discussed through numerical computations. The observations reveal that an increase of the discharge field decreases the stress intensity factor and the energy release rate. An eccentric penny-shaped crack is easier to propagate than a mid-plane one in a piezoelectric layer, and the geometry of the crack along with the layer thickness have significant influences on the electrostatic traction acting on the crack faces. The solutions for a penny-shaped dielectric crack in an infinite or a semi-infinite piezoelectric material can be obtained easily.     

氯化镁介质中氧化铝表面的相互作用力

利用原子力显微镜研究了氯化镁介质中氧化铝表面的相互作用力随盐浓度、ｐＨ的变化规律．在中性条件下;当ＭｇＣｌ_２盐浓度由１０^－５ｍｏｌ／Ｌ增加到１０^－2ｍｏｌ／Ｌ时,长程排斥作用由于双电层压缩,作用范围从一百多纳米减弱到十几纳米,实验测得的双电层厚度的实际值与理论值较好的吻合．保持ＭｇＣｌ_２介质浓度不变;ｐＨ由３．６４变化到９．０９;氧化铝表面的相互作用始终表现为排斥力,与测得的Ｚｅｔａ电位值始终为正值相一致．当ｐＨ＝９．５时,由于镁离子的水合氢氧化物在氧化铝表面的特性吸附,产生了短程非静电徘斥力,首次用原子力显微镜证实了Ｍｇ^２＋特性吸附层的存在,厚度约为５ｎｍ。     

Low-frequency dielectric relaxation in 5TsB liquid crystals controlled by the ion adsorption-desorption processes

Stable liquid-crystalline states with various ε′ and ρ values were obtained in planar-oriented 5TsB liquid crystals by exposure to constant and alternating electric fields. The initial portion of the low-frequency dispersion of ε′ and ε″ obeys the Debye equation for both strictly planar and nonplanar (“oblique”) orientation of molecules.     

横向可压缩电流变夹层梁的振动特性

讨论了电流变夹层梁在考虑电流变材料层横向可压缩时的动力学特性。在建模过程中将电流变材料视为可压缩的粘弹性材料, 假设电流变材料层的横向位移随厚度变化。基于一阶剪切变形理论和能量方法建立了电流变夹层梁的挤压-剪切动力学模型, 并采用有限元方法进行了离散求解。通过对悬臂梁的仿真和实验分析得出:在电流变夹层梁的振动过程中, 上、下约束层的横向位移并不完全相等, 在低频阶段相差不大, 但在高频阶段较为明显; 加大外加电场的强度, 可以减小横向位移的差值; 而电流变层厚度的增加, 将使横向位移的差值加大。      

Postbuckling of pressure-loaded FGM hybrid cylindrical shells in thermal environments

A postbuckling analysis is presented for a functionally graded cylindrical shell with piezoelectric actuators subjected to lateral or hydrostatic pressure combined with electric loads in thermal environments. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the shell surface and varied in the thickness direction and the electric field considered only has non-zero-valued component E_Z. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and piezoelectric layers are assumed to be temperature-dependent. The governing equations are based on a higher order shear deformation theory with a von Kármán–Donnell-type of kinematic nonlinearity. A boundary layer theory of shell buckling is extended to the case of FGM hybrid laminated cylindrical shells of finite length. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of pressure-loaded, perfect and imperfect, FGM cylindrical shells with fully covered piezoelectric actuators under different sets of thermal and electric loading conditions. The results reveal that temperature dependency, temperature change and volume fraction distribution have a significant effect on the buckling pressure and postbuckling behavior of FGM hybrid cylindrical shells. In contrast, the control voltage only has a very small effect on the buckling pressure and postbuckling behavior of FGM hybrid cylindrical shells.     

The Effect of Axial Concentration Gradient on Electrophoretic Motion of a Charged Spherical Particle in a Nanopore

The electrophoretic motion of a charged spherical nanoparticle along the axis of a nanopore connecting two fluid reservoirs, subjected to an axial electric field and electrolyte concentration gradient, has been investigated using a continuum model. The model consists of the Poisson and Nernst–Planck equations for the electric potential and ionic concentrations and the Stokes equations for the hydrodynamic field with zero gravity. In addition to the electrophoresis generated by the externally imposed electric field, the particle also experiences diffusiophoresis arising from the externally imposed concentration gradient. The effects of the diffusiophoresis on the axial electrophoretic motion are examined with changes in the ratio of the particle size to the thickness of the electric double layer (EDL), and the imposed concentration gradient. Since the EDL thickness, the particle size, and the nanopore size are of the same order of magnitude, the diffusiophoresis is dominated by the induced electrophoresis driven by the generated electric field arising from the double-layer polarization (DLP). For a relatively small κa _p , the ratio of the particle size to the EDL thickness, the diffusiophoresis is dominated by the induced electrophoresis from the type II DLP, which propels the particle toward regions with lower salt concentration. Depending on the magnitude and direction of the externally imposed concentration gradient, the electrophoretic motion can be accelerated, decelerated, and even reversed by the diffusiophoresis.     

电场作用下竖直板表面特性对霜层生长的影响

研究了自然对流条件下直流电场对竖直表面上霜晶初始形态的影响,拍摄了不同电场下的霜晶形态,研究发现,在成霜初期,电场越强,冷壁面上形成的水珠越小。当水珠完全冻结后,所形成的冰柱在一定时间内不断增大。在适当的电场下,亲水表面比裸铜表面能够更好地抑制霜层的厚度。对亲水表面结霜质量的研究表明,电场使结霜质量增加,并且结霜质量随着电场的增大而增大。     

Piezoelectric study on confocally multicoated elliptical inclusion

Within the framework of linear piezoelectricity, an effective method is developed and used to derive an analytical solution for the problem of a confocally multicoated elliptical inclusion embedded in an unbounded matrix which is subjected to arbitrary electromechanical loadings. Each layer of the composite is assumed to have different material constants, but has the same material orientation with x₃ being the poling direction. The alternating technique in conjunction with the method of analytical continuation is applied to derive the general series solution of electric field and displacement field for each layer of the composite. This approach has a clear advantage in deriving the solution to the heterogeneous problem in terms of the solution to the corresponding homogeneous problem. Several specific solutions are provided in closed form, which are verified by comparison with the existing ones. Some numerical results are provided to investigate the influence of material combinations and different electromechanical loadings on the shear stress and electric field. Besides, they also show that the derived solutions are well satisfied with the boundary conditions.     

基于三阶剪切变形理论的压电功能梯度板静力学等几何分析

针对压电功能梯度板的静力学问题,建立了一种基于三阶剪切变形理论的等几何分析求解方法.其中,定义功能梯度板的材料属性为板厚方向的幂函数分布,并假设压电功能梯度板中的机械位移场与电势场相互独立.利用压电材料的第二类本构方程以及哈密顿变分原理,推导出压电功能梯度板的相关等几何有限元方程.在压电功能梯度板的自由振动分析中,研究...