Time-averaged total force on a dipolar sphere in an electromagnetic field

We establish the time-averaged total force on a subwavelength-sized particle in a time-harmonic-varying field. Our analysis is not restricted to the spatial dependence of the incident field. We discuss the addition of the radiative reaction term to the polarizability to deal correctly with the scattering force. As an illustration, we assess the degree of accuracy of several previously established polarizability models.     

Acoustic radiation force on a multilayered sphere in a Gaussian standing field

We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach. An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid. The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed, with particular emphasis on the shell thickness of every layer, and the width of the Gaussian beam. The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka, as well as the shell thickness of each layer. This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave, which may benefit the improvement and development of acoustic control technology, such as trapping, sorting, and assembling a cell, and drug delivery applications.     

Capillary pressure and contact line force on a soft solid

The surface free energy, or surface tension, of a liquid interface gives rise to a pressure jump when the interface is curved. Here we show that a similar capillary pressure arises at the interface of soft solids. We present experimental evidence that immersion of a thin elastomeric wire into a liquid induces a substantial elastic compression due to the solid capillary pressure at the bottom. We quantitatively determine the effective surface tension from the elastic displacement field and find a value comparable to the liquid-vapor surface tension. Most importantly, these results also reveal the way the liquid pulls on the solid close to the contact line: the capillary force is not oriented along the liquid-air interface, nor perpendicularly to the solid surface, as previously hypothesized, but towards the interior of the liquid.     

Radiation forces on a Rayleigh dielectric sphere in a patterned optical near field

We report on the study of the radiation forces exerted on a Rayleigh dielectric particle by a patterned optical near-field landscape at an interface decorated with resonant gold nanostructures. This configuration allows for the generation of a large array of surface subwavelength optical traps from an extended collimated beam, which may be of interest for parallel optical manipulation and sorting of submicrometer objects.     

Electric fields inside and outside an anisotropic dielectric sphere

Analytical expressions of electric fields inside and outside an anisotropic dielectric sphere are presented by transforming an anisotropic medium into an isotropic one based on the multi-scale transformation of electromagnetic theory. The theoretical expressions are consistent with those in the literature. The inside electric field, the outside electric field and the angle between their directions are derived in detail. Numerical simulations show that the direction of the outside field influences the magnitude of the inside field, while the dielectric constant tensor greatly affects its direction.     

Mean force on a small sphere in a sound field in a viscous fluid

A mean force exerted on a small rigid sphere by a sound wave in a viscous fluid is calculated. The force is expressed as a sum of drag force coming from the external steady flow existing in the absence of the sphere and contributions that are cross products of velocity and velocity derivatives of the incident field. Because of the drag force and an acoustic streaming generated near the sphere, the mean force does not coincide with the acoustic radiation pressure, i.e., the mean momentum flux carried by the sound field through any surface enclosing the sphere. If the sphere radius R is considerably smaller than the viscous wave penetration depth delta, the drag force can give the leading-order contribution (in powers of delta/R) to the mean force and the latter can then be directed against the radiation pressure. In another limit, delta< or =R, the drag force and acoustic streaming play a minor role, and the mean force reduces to the radiation pressure, which can be expressed through source strengths of the scattered sound field. The effect of viscosity can then be significant only if the incident wave is locally plane traveling.     

Electrostatic charging of a conducting sphere using another conducting sphere at constant voltage

This study uses results of classical electrostatics to predict the resulting voltage of a conducting sphere that is charged by a second sphere maintained at a constant voltage. The voltage of the charged sphere is calculated as a function of the charging voltage and the size ratio of the two spheres. Theoretical predictions are verified experimentally using conducting spheres of various sizes and a Faraday ice pail apparatus. The results may seem somewhat counterintuitive. For example, a charging sphere held at 100 V will charge another sphere of equal size only to 69.3 V by contact.     

Electric charge and field in the meniscus of a dielectric fluid

Using the conformal mapping method, we calculate the electric field at the tip of a high-voltage electrode mounted in the injector of fluid particles. The space charge of the dielectric fluid charged from the high-voltage electrode of the injector of the fluid charged particles is determined. We present the results of simulation of the charge and field in the meniscus for VM-1vacuum oil.     

Electric field localizations in thin dielectric films with thickness non-uniformities

Thickness non-uniformities in electrostatic capacitors and in electroactive polymers – arising from manufacturing processes or electromechanical induced inhomogeneous deformations – may lead to drastic charge and electric field localizations and, ultimately, to an anticipated device failure. Based on a geometric interpretation of the Gauss equation enlightening the effect of the electrode curvature, we obtain an analytic expression of the electric field and of the surface charge density localization for non perfectly planar capacitors with symmetric thickness non-uniformities. The efficiency of the model is exploited by analyzing specific boundary value problems of technological interest.     

On the low vibration modes observed in a sphere submitted to a tangential contact force

In this paper we discuss the existence of translational and rotational displacements of a sphere submitted to a tangential contact force. On the basis of the Bogdanov and Skvortsov’s works [A.N. Bogdanov, A.T. Skvortsov, Sov. Phys. Acoust. 38 (1992) 224–226.] the dispersion equation has been established and solved for any value of the frequency in the case of the linear approximation. The present experimental analysis confirms that it exists two branches: an upper branch associated to the translation of the sphere and a lower branch characteristic of the rotation of the bead.     

用电象法计算均匀外电场中导体球表面上感生电荷的分布

用电象法求出了均匀外电场中导体球表面上感生电荷的分布.     

带电细圆环与导体球壳系统的场分布

先依电象法,推导均匀带电圆环在金属导体球壳内的"象电荷";再在球坐标系下,根据电场强度的计算公式与Tay-lor展开式,计算出均匀带电细圆环在全空间的电场分布的级数形式解;进而结合唯一性定理和电场的叠加原理,获得带电细圆环与导体球壳系统的空间场分布.     

Interaction force between a bubble and a solid particle in a sound field

The time-averaged interaction force exerted by a sound field between a gas bubble and a solid spherical particle is examined. An approach is developed allowing the force to be calculated for small separations between the bubble and the particle. The results obtained are compared with the existing asymptotic equation derived for large separations. It is shown that when the bubble and the particle are closely spaced, both the magnitude and the sign of the force are different from those predicted by the asymptotic equation, resulting in new interesting effects.     

Force and torque on a sphere with electric dipole moment moving in a dielectric fluid in the presence of a uniform magnetic field

The torque exerted by a magnetic field on a sphere with permanent electric dipole moment moving steadily in a dielectric fluid is calculated to lowest order in the dipole moment. Hence the force exerted on a steadily rotating sphere with electric dipole moment is found by Onsager symmetry. The modification from the vacuum values of torque and force depends only on the slip parameter and the static dielectric constant of the fluid. It is suggested that for a macroscopic ferro electric sphere the calculated effects could be measured experimentally without great difficulty.     

Energy,force and field strength in a system of two charged conducting balls

A calculation has been performed for the interaction force and the field strength in a system consisting of two charged conducting balls in three cases: 1) the balls are maintained at the preset potentials; 2) the balls are insulated and have fixed charges; 3) one of the balls has the preset potential, and the second one has the preset charge. Experimental measurements of forces in the first and third cases were performed and fair agreement with calculations was confirmed. A calculation method has been suggested, and the electric field strength on the nearest poles of the balls has been calculated for the three mentioned cases. A good agreement with the other authors' calculation results has been demonstrated.     

Electric field effects on nucleation during phase transitions of a dielectric fluid

Using the thermodynamic theory of phase transitions, it is shown that an electric field increases the critical size and work for bubble nucleation in a superheated liquid and impedes the process; it decreases the critical size and work for liquid droplet formation in a supercooled vapour and enhances the process.