Effect of X-rays on effective nonlinearity of crystals of the triglycine sulfate group

The effect of low irradiation doses on the threshold behavior of the effective permittivity of crystals of the triglycine sulfate group in an ac electric field has been studied. It has been shown that the effect of radiation-induced radicals on the domain structure of the studied crystals is not identical and is controlled by the nature of the previously introduced defects. Interaction energies of domain walls with defects have been calculated.     

A model for the dependence of the dielectric loss factor of a ferroelectric on the microwave signal amplitude

The nonlinear phenomena occurring in ferroelectrics were studied using a model for the dependence of the ferroelectric polarization on the amplitude of the applied field. The inclusion of the static internal defect field made it possible to determine the dependence of the complex permittivity of a ferroelectric on the dc electric field strength. The dependences of the complex permittivity and the dielectric loss factor on the amplitude of microwave oscillations were obtained using the Poynting theorem for harmonic microwave oscillations.     

Influence of defects on the conductivity of graphene within the effective theory approach

The results of the Monte Carlo simulations of graphene with structural defects are presented. The calculations are performed within an effective quantum field theory with non-compact 3 + 1-dimensional Abelian gauge field and 2 + 1-dimensional Kogut-Susskind fermions. It was found that defects shift the semimetal-insulator phase transition point towards higher values of a substrate permittivity.     

Anomalous surface deceleration of a domain wall in an amorphous ferromagnet

On soft magnetic amorphous specimens, a rapid decrease in the surface amplitude of 180° domain wall oscillations relative to the bulk amplitude is observed with increasing frequency of the magnetizing field. The dynamics of the domain wall is studied by a magnetooptical method at the specimen surface and by the induction method in the bulk. The results of the experiment disagree with the theory, which takes into account the effect of eddy currents and predicts that, with increasing frequency, the surface amplitude of the domain wall oscillations should decrease slower than the bulk amplitude. The observed behavior of the domain wall is explained by its interaction with macroscopic defects at the specimen surface. This interaction gives rise to unsteady chaotic surface wall displacements, which lead to an increase by several orders of magnitude in the effective surface damping parameter in the Landau-Lifshits equation.     

Effective permittivity of the system of metal nanoislands in strong electric fields

The effect of the electric field on the value and sign of the low-frequency effective permittivity of metal island films is studied. It is shown that the permittivity in island metal films can be both positive and negative. The permittivity of some samples changed sign with the polarity of the applied electric field. Film polarization mechanisms are considered.     

Dynamic conductivity of composites of fractal structure

We have studied the dynamic conductivity of a composite consisting of well- and weak-conducting components with random fractal structure. In order to calculate effective properties of composite medium, we used hierarchic structure model and innovative iterative averaging method based on renormalization group transformations idea. Our results show, that the behavior of a composite over a magnetic field become even more complicated.Unusual peaks and oscillations appear in frequency dependencies of effective conductivity, permittivity and other properties. We discuss the influence of fractal parameters of the composite structure on such unusual behavior of effective properties.     

Transformation of a monochromatic plane wane by the pulse-periodic time modulation of an infinite medium

An exact solution to the problem of the transformation of a monochromatic plane wave by a finite train of equally spaced rectangular pulses of permittivity and conductivity of an infinite medium is considered. The permittivity pulse train is shifted relative to the conductivity pulse train by an arbitrary time. The problem is studied analytically in terms of the second-order Volterra integral equation describing the electromagnetic wave transformation in a medium with time-dependent parameters. The equation is solved using the resolvent technique. Expressions for the amplitude of the transformed electric field component for any time instant at any spatial point are derived and analyzed.     

Vortex System Dynamics upon Pulsed Magnetization of a HTS

A numerical investigation of the response of a HTS with different numbers of defects to the action of rectangular magnetic field pulses with a varying amplitude is carried out. The time dependences of a magnetic field trapped by the superconductor are calculated at different pulse parameters. The values of the HTS response to pulsed and gradual magnetization and demagnetization of the sample are compared, which reveals that magnetic flux trapping is more efficient under the action of pulses. A feature in the behavior of the vortex lattice acted on by field pulses is established, which relates to correlation between the number of defects and pulse amplitude. Flux trapping is shown to have a maximum dependent on the concentration of defects at each pulse amplitude.     

Analysis of the electric field behavior in the vicinity of a triple junction,using finite elements method computational simulations

The authors studied the electric field behavior in the vicinity of a triple junction, composed by metal, vacuum and dielectric parts, using computational simulations. A bi-dimensional model was constructed using ANSYS MAXWELL to analyze the magnitude of the electric field as a function of the contact angles of the materials. The results showed that a field enhancement or reduction could occur in vacuum for certain contact angles. The influence of the dielectric permittivity was also investigated, and the conclusions showed that the maximum electric field enhancement is proportional to the dielectric permittivity.     

Long-range surface plasmon polariton modes with a large field localized in a nanoscale gap

A planar five-layer waveguide with a metal-insulator (with the low permittivity)-metal structure embedded in a high-permittivity dielectric is theoretically studied. A long-range surface mode draws special attention because of its superior properties of low attenuation and a large field localized inside the nanoscale middle gap provided with permittivity-contrast. Effects of the surrounding permittivity and the metal film thickness are investigated, and the electric field amplitude in the gap can be dozens of times higher than that at the outer interfaces. This plasmonic structure may have potential applications in integrated photonic devices.     

Effect of low-angle boundaries on the dielectric properties of epitaxial Ba0.8Sr0.2TiO3 films

The effect of low-angle boundaries on the dielectric properties of epitaxial Ba_0.8Sr_0.2TiO₃ films is studied by comparing films differing in crystalline-block size. It is found that the permittivity diminishes considerably when the block sizes are reduced. The maximum of the temperature-dependent permittivity is shifted towards lower temperatures, and the sensitivity of the permittivity to an electric field is reduced. Moreover, it is found that the maximum in the permittivity temperature dependence is displaced towards lower temperatures when the applied measured voltage is increased and becomes higher than the coercive voltage. The width of a hysteresis loop decreases significantly when the frequency of the controlling field is reduced. The reasons for the observed behavior are analyzed.     

Modeling the electrical characteristics of periodic dielectric media

The dispersion of the effective permittivities of two inhomogeneous matrix systems with unidirectional fiber inclusions with a square cross section is studied. Interpolation formulas for the effective permittivity as a function of the frequency are obtained, whose range of applicability is determined through physical modeling and comparison with known systems of equations admitting exact solutions. It is established that the effective loss factor exhibits anomalous behavior in the vicinity of the critical concentration of inclusions.     

Absorption losses in periodic arrays of thin metallic wires

We analyze the transmission and reflection of electromagnetic waves calculated from transfer matrix simulations of periodic arrangements of thin metallic wires. The effective permittivity and the absorption of the arrangements of wires are determined. Their dependence on the wire thickness and the conductance of the metallic wires is studied. The cutoff frequency, or effective plasma frequency, is obtained and compared with analytical predictions. It is shown that the periodic arrangement of wires exhibits a frequency region in which the real part of the permittivity is negative while its imaginary part is very small. This behavior is seen for wires with thickness as small as 17 microm with a lattice constant of 3.33 mm.     

Surface waves in a crystal with switching Kerr nonlinearity

In this paper, we explore transverse electric surface waves propagating along the crystal with jump change of Kerr nonlinearity in dependence on field amplitude. The dielectric permittivity in the proposed model of nonlinearity is characterized by abruptly changing unperturbed dielectric constant and Kerr nonlinearity coefficient from one value to another when field amplitude exceeds the threshold value of the switching field. This allows to find exact solutions of model equations in different cases of nonlinearity signs, and to obtain the dependence of wave characteristics, including total power flux, on effective refractive index in explicit form. Such solutions describe two new types of nonlinear surface waves with specific structure depending on electric field amplitude. We derive the conditions of surface domain formation. It is found that the largest percentage of radiation is concentrated within the domain.     

Reversible permittivity of a photosensitive relaxor ferroelectric

The reversible permittivity of barium strontium niobate, a photosensitive relaxor ferroelectric, doped with lanthanum and cerium is investigated in the dark and under illumination with a power density of 0.22 mW/cm². The permittivity is measured under a combined effect of a weak ac electric field at a frequency of 1 MHz and a slowly varying periodic field E _b with an amplitude of ±2.3 kV/cm. It is shown that the illumination significantly increases the permittivity, changes the dependence of the permittivity on the periodic field E _b , and eliminates the possible unipolarity of the crystal, thus significantly improving the reproducibility of the permittivity during repeated measurements.     

阵元固体指向性补偿对超声全聚焦成像的 优化研究*

超声全聚焦成像中,声波的传播受到阵元指向性的影响,位于阵元不同方位的缺陷成像幅度不同。缺陷相对阵列中心偏角越大,回波幅度越低,容易造成漏检。为提高超声全聚焦算法对固体中大偏角缺陷的成像能力,该文引入了矩形阵元固体指向性函数,建立了基于固体指向性补偿的超声全聚焦优化算法,利用指向性系数对不同角度区域的成像进行幅值补偿。实验结果表明,相对于基本超声全聚焦和传统指向性补偿的超声全聚焦算法,该文固体指向性优化算法对大偏角缺陷的成像幅度补偿效果更好,检测灵敏度更高,有效避免了缺陷漏检,扩展了超声全聚焦算法检测范围。     

Anomalously high low-frequency effective permittivity in a system of metal nanoislands

The low-frequency effective permittivity in a system of Co, W, and FeNi metal nanoislands in an electric field is investigated. The permittivity of films is determined from analyzing the dependences of the susceptance of the films on the temperature and the electric field. It is found that the effective permittivity of the structures under investigation has an anomalously high positive value (10⁷–10⁸) and that an increase in the electric field leads to a decrease in the effective permittivity and an increase in the electrical conductivity of the films. The nature of the high effective permittivity of the structures is governed by the island structure of the metal films and associated with the polarization of dipoles formed by pairs of negatively and positively charged metal nanoislands.     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

Phenomenological model of relaxor behavior

A phenomenological model is proposed for describing the behavior of ferroelectrics with the diffuse phase transition near the permittivity maximum in the low-temperature phase. The behavior in this temperature range is shown to be related to the dynamics of formation of polarized state regions near defects with localized charges. The delay in the transition to the uniformly polarized state in the low-temperature phase is discussed.     

Low-frequency polarization relaxation in PMN + 2% Li2O ferroelectric ceramics in the region of diffuse phase transition

Studies of dielectric nonlinearity in lead magnoniobate ceramics doped with lithium show that at a certain value of external field amplitude E, two peaks appear on the temperature dependences of effective dielectric permittivity ?_eff′(T). They are caused by the dynamics of the polar regions in the vicinity of diffuse phase transition and by variation in their volume under the action of field E.