Two-particle cluster integral in the expansion of the dielectric constant

We study in detail the two-particle cluster integral in the cluster expansion for the effective dielectric constant of a suspension of spherically symmetric polarizable inclusions embedded in a uniform medium. Although our form for the integrand differs from that derived earlier by Finkel'berg and by Jeffrey, we show that the integral is equivalent. The two-body dielectric problem for particles with an arbitrary radial dependence of the dielectric constant is solved by an expansion in spherical harmonics. Numerical results for some special models illustrate the importance of multipole contributions to the effective dielectric constant.     

Cluster expansion for the dielectric constant of a polarizable suspension

We derive a cluster expansion for the electric susceptibility kernel of a dielectric suspension of spherically symmetric inclusions in a uniform background. This also leads to a cluster expansion for the effective dielectric constant. It is shown that the cluster integrals of any order are absolutely convergent, so that the dielectric constant is well defined and independent of the shape of the sample in the limit of a large system. We compare with virial expansions derived earlier in statistical mechanics for the dielectric constant of a nonpolar gas. In these expansions the virial coefficients are given by integrals which are only conditionally convergent.     

Effective dielectric constant of dilute polydisperse suspensions of spheres

We study the effective dielectric constant of a dilute, polydisperse suspension of spheres embedded in a uniform background. We consider a frequency region where the dipole polarizability of individual spheres exhibits a resonance. We evaluate the effective dielectric constant to second order in the volume fraction employing the dipole approximation, which in previous work has been shown to be applicable in resonance. We apply our results to suspensions of spheres with identical and uniform dielectric constant, assuming a log-normal distribution of sphere radii.     

Multipole contributions to the effective dielectric constant of suspensions of spheres

We study multipole contributions to the effective dielectric constant of dilute suspensions of uniform spheres. It is shown that for frequencies near the plasma resoance multipole contributions are negligible in comparison with the dipole contributions. Outside resoance multipolar corrections to the Clausius-Mossotti formula are of the same order of magnitude as the dipolar ones. We argue that in resonance the dipole approximation should be valid also for more complicated sphere models.     

Ab initio study of dielectric function of C-substituted single walled boron nanotubes

We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant ε ₁(ω) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.     

Analysis of the temperature influence on the plasma reflectance by a new FDTD method

We apply the shift-operator FDTD (SO-FDTD) method for calculating dispersive media plasmas. We write the dielectric constant of a dispersive medium as a rational fractional function and derive the relation between D and E in the time domain. For a uniform, approximately isothermic, isotropic, warm-collision-plasma slab, the reflection coefficient of electromagnetic waves can be calculated using the SO-FDTD method. We study the influence of temperature on the collisions and absorption of electromagnetic waves in the plasma and discuss the regularity of the relationships obtained.     

Analysis of the electrostatic force on a dielectric particle with partial charge distribution

This paper presents the analysis of the electrostatic force acting on a charged dielectric particle on a grounded plane. The force has been determined by a numerical field calculation method to make clear the effect of particle dielectric constant and charge distribution on the particle surface. The charge is treated to be distributed in three ways: (a) uniformly over entire surface, (b) partially on the upper, or (c) on the lower part of a particle. The calculation results show that, if a particle with dielectric constant ?_p = 3 is partially charged on the lower part by a zenith angle π/2, π/4 and π/8, the force shall be higher by 0.7, 4.3 and 20 times, respectively, than that for a uniform charging with the same charge amount. On the other hand, the force becomes weaker when charge is on the upper part. The effect of the particle dielectric constant is found to be dependent on the charge distribution. With charge uniform on the entire surface or on the upper part, the force always increases with the dielectric constant. However, when surface charge is restricted to a small area at the lower part of the particle (θ_q < π/4), the force may decrease with increasing the dielectric constant.     

溶胶-凝胶法制备BaTiO3/SrTiO3多层膜的介电增强效应

采用溶胶凝胶法,在PtTiSiO2Si衬底上逐层制备了BaTiO3SrTiO3多层膜.从多层膜的XRD图可看出明显的双峰,分别对应为BaTiO3和SrTiO3的特征峰,表明样品已形成了多层膜结构.与同厚度的Ba05Sr05TiO3单层膜比较,BaTiO3SrTiO3多层膜的介电系数得到了明显的增强,在频率为10kHz时,周期为66nm的BaTiO3SrTiO3多层膜相对于同厚度的Ba05Sr05TiO3薄膜的介电系数从245增强到595,而损耗依然保持较低,分别为0029和0033.研究同时表明,BaTi 关键词： 溶胶-凝胶法 多层膜 介电增强     

Observation of surface gap solitons in semi-infinite waveguide arrays

We report on the observation of surface gap solitons found to exist at the interface between uniform and periodic dielectric media with defocusing nonlinearity. We demonstrate strong self-trapping at the edge of a LiNbO3 waveguide array and the formation of staggered surface solitons with propagation constant inside the first photonic band gap. We study the crossover between linear repulsion and nonlinear attraction at the surface, revealing the mechanism of nonlinearity-mediated stabilization of the surface gap modes.     

Static dielectric properties of Stockmayer fluids

Dielectric constants for the Stockmayer fluid are computed both from the equilibrium fluctuations of the polarization and from the polarization response to an applied field in a molecular dynamics simulation with periodic boundary conditions and with the dipole interactions treated by the Ewald method. The dielectric constant at finite wavelength is obtained from a Kirkwood-like expression, while for uniform polarization fluctuations a different expression applies due to the absence of surface effects in the Ewald calculation. The results are nearly independent of the number (up to 500) of particles investigated, even at large values of the dipole moment. The dielectric constants obtained from the approximate solution of the hypernetted chain integral equation are considerably larger than the molecular dynamics results except at low dielectric constants. The external field simulation permits study of the non-linear dependence of the dielectric constant on the magnitude of the applied electric field.     

Bounds for the complex dielectric constant of a two-phase composite

We study the effective dielectric constant of a two-phase composite for the case where the dielectric constants of the two components are complex. Milton has derived a sequence of narrowing bounds in the complex plane limiting the possible values of the effective dielectric constant, assuming that certain geometrical coefficients characterizing the medium are known. We cast Milton's bounds in a different form, making use of auxiliary functions introduced by Bergman. We derive explicit expressions for the bounds up to third order and compare values for the corresponding geometrical coefficient derived for different geometries.     

Magnetodielectric effects from spin fluctuations in isostructural ferromagnetic and antiferromagnetic systems

We report on the effects of spin fluctuations, magnetic ordering, and external magnetic field on the dielectric constant of the ferromagnet SeCuO3, and the antiferromagnet TeCuO3. A model based on the coupling between uniform polarization and the q-dependent spin-spin correlation function is presented to explain the different behaviors for these isostructural compounds. The large magnetocapacitance near the transition temperature in the ferromagnet SeCuO3 suggests routes to enhancing the magnetodielectric response for practical applications.     

Chloride Assisted Growth of Aluminum Nitride Nanobelts and Their Enhanced Dielectric Responses

通过氯化物辅助的气-固生长方法成功地制备出了大量单晶的氮化铝纳米带. X射线衍射、透射电子显微镜以及选区衍射分析表明,所制备的纳米带是纯度高、结构均匀的单晶体,并具有六方的晶体结构. 显微观察表明所获得的氮化铝纳米带没有缺陷,其生长方向为[0001]方向. 测量了产物在50 Hz 到5 MHz范围内的介电频谱,谱图分析表明样品中的界面对样品的介电特性有很大的影响. 室温条件下,与氮化铝微米粉相比,氮化铝纳米带的介电常数高得多,并在低频情况下尤为显著.     

Importance of polarization processes near the electrodes in measurements of the dielectric constant of conducting media

We attempt in the present work to analyze from a unified viewpoint the complicated laws which are observed in experiments when the dielectric constant of media with rather high positive conductivity is measured. The proposed method allows the calculation of the basic parameters of a measuring cell and of the dielectric constant of media.     

Spatial Uniformity of Atmospheric Pressure Discharges: A Simulation Study

Spatial uniformity is important in most applications of dielectric barrier discharges operating at atmospheric pressure. However, such uniformity is not easily achieved. Under many conditions, a filamentary structure usually develops. In this paper, we employ a two‐dimensional self‐consistent fluid model to explore the influence of several factors on the evolution of spatial structure of dielectric barrier discharges. In particular, we contrast the behavior of discharges in pure helium and He‐N₂ gas mixture, which represent the reduction in breakdown voltage of gas during the evolvement of uniform glow discharge plasma. The transformation from filamentary to uniform mode of discharge plasma is analyzed by the phenomenon of coalescence of filaments and we investigate the effect of several external discharge parameters, such as driving frequency and effect of overvoltage, and the dielectric constant of the barrier material for the uniform and filamentary discharge plasmas. This simulation study is useful to describe the spatio‐temporal profiles of electron density in different phases of the filamentary, uniform Townsend and glow discharge regimes under various constraints. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Existence of gaps in the spectrum of periodic dielectric structures on a lattice

We consider the finite-difference counterpart, i.e., the true lattice analog, of Maxwell's equations and equations that govern the propagation of acoustic waves in a medium with a periodic dielectric structure. In particular, the vector nature of electromagnetic waves is fully taken into account. The existence of true gaps for these lattice models is proved for a two-component medium for which the dielectric constant is everywhere real and positive, and the dielectric constant of the background is essentially larger than the one corresponding to the embedded component.     

Dynamics of the destruction and rebuilding of a dipole gap in glasses

After a strong electric bias field is applied to the polyester glass Mylar at temperatures in the mK range, its dielectric constant increases and then decays logarithmically in time. We observed its dielectric response for several temperatures and different field sweeps. Starting from the dipole gap theory, we developed a model suggesting that the change in dielectric constant after transient application of a bias field is only partly due to relaxational processes. In particular, nonadiabatic driving of tunneling states (TSs) by applied electric fields causes additional dielectric response. Also, we find that for T less, similar 50 mK the relaxation of TSs is caused primarily by mutual interactions.     

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches have made use of simple analytical formulas to analyze the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tip-sample electrostatic interaction in the following setup: an insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.     

Quantization and generation of squeezed states of electromagnetic field in a cavity with variable parameters

Quantization of an electromagnetic field in a cavity filled with a uniform medium having a time-varying dielectric constant and in a cavity with a moving wall is considered. It is shown that squeezed and correlated states of the field can be generated. The possible limits of the squeezing and correlation coefficients are indicated. Two methods of parametric buildup of field modes, by variation of the dielectric constant and by vibrating the cavity wall at double the frequency, are compared.Presented at the International Workshop on Squeezed and Correlated States in Quantum Optics, Moscow, December 3–7, 1990.     

Applications of the expanded basis method to study the properties of photonic crystals with frequency-dependent dielectric functions and dielectric losses

Band structures of two-dimensional photonic crystals (PCs) made of polar material with frequency-dependent dielectric constant are calculated by using an expanded basis method. The effect of the polariton gap (PG) of polar material on the photonic band gaps (PBGs) is explored. It is found that the PBGs are significantly modified near the PG, where the abrupt change of the dielectric constant appears. The feature of electromagnetic (EM) field is revealed when the frequency is located in the flat band. We display the equifrequency-surface configuration of the localized field and the spacial distributions of field. We observe the existence of several equi-ω curves for a specified frequency and the localized field distribution exhibiting various different patterns, dependent of the mode index. We also study the influence of the dielectric losses of the polar material on dispersion and find that the change of the real part of the Bloch wave vector is crucially related to the real part of the dielectric constant and the attenuated length is determined by its imaginary part.