Discontinuity Of Permittivity Research Articles

Space Charge Characteristics in Epoxy Resin Impregnated Paper under AC and AC-DC Superimposed Electric Fields

In this paper, charge distributions in three-layered epoxy resin and epoxy resin impregnated paper samples under AC and AC-DC superimposed electric fields are measured by the improved high-speed pulsed electro-acoustic system. To exclude the interferences caused by the discontinuity of relative permittivity, a method to distinguish between net dipolar charges and free charges is proposed. Through analysis, the influences of frequency, AC component and DC component on the charge transport and trapping characteristics in multi-layered epoxy composites are obtained, which could provide important reference to the structural design and optimization of converter transformer bushings.

Integration and High-Temperature Characterization of Ferroelectric Vanadium-Doped Bismuth Titanate Thin Films on Silicon Carbide

4H-SiC electronics can operate at high temperature (HT), e.g., 300°C to 500°C, for extended times. Systems using sensors and amplifiers that operate at HT would benefit from microcontrollers which can also operate at HT. Microcontrollers require nonvolatile memory (NVM) for computer programs. In this work, we demonstrate the possibility of integrating ferroelectric vanadium-doped bismuth titanate (BiTV) thin films on 4H-SiC for HT memory applications, with BiTV ferroelectric capacitors providing memory functionality. Film deposition was achieved by laser ablation on Pt (111)/TiO2/4H-SiC substrates, with magnetron-sputtered Pt used as bottom electrode and thermally evaporated Au as upper contacts. Film characterization by x-ray diffraction analysis revealed predominately (117) orientation. P–E hysteresis loops measured at room temperature showed maximum 2Pr of 48 μC/cm2, large enough for wide read margins. P–E loops were measurable up to 450°C, with losses limiting measurements above 450°C. The phase-transition temperature was determined to be about 660°C from the discontinuity in dielectric permittivity, close to what is achieved for ceramics. These BiTV ferroelectric capacitors demonstrate potential for use in HT NVM applications for SiC digital electronics.

THE CHERENKOV EMISSION IN REGULAR AND RANDOM PHOTONIC CRYSTALS

We systematically study the Cherenkov optical emission by a nonrelativistic charge uniformly moving in parallel to surface of a photonic crystal by FDTD simulations. It is found that a near-static structure of field oscillations produced by a discontinuity of dielectric permittivity in surface of photonic lattice is generated. Such oscillations have large amplitude in Cherenkov group cone and generate a number of well defined spectral resonances corresponding to eigenmodes of the photonic grid. The dynamics and field properties in photonic lattice with random vacancies are investigated too. It is found that even at medium level of a random perturbation the field shape shows the structural stability of the Cherenkov emission field in a photonic crystal.

FDTD Method for Piecewise Homogeneous Dielectric Media

In this paper, we consider a numerical solution of Maxwell’s curl equations for piecewise uniform dielectric medium by the example of a one-dimensional problem. For obtaining the second order accuracy, the electric field grid node is placed into the permittivity discontinuity point of the medium. If the dielectric permittivity is large, the problem becomes singularly perturbed and a contrast structure appears. We propose a piecewise quasi-uniform mesh which resolves all characteristic solution parts of the problem (regular part, boundary layer and transition zone placed between them) in detail. The features of the mesh are discussed.

Asymptotic representation of the electromagnetic field of a dielectric waveguide near a corner point of the line of discontinuity of permittivity

The behavior of the electromagnetic field of a waveguide near a corner point of a line of discontinuity of the permittivity is studied.

The interaction between plasma filaments in dielectric barrier discharges and liquid covered wounds: electric fields delivered to model platelets and cells

The treatment of wounds by atmospheric pressure plasmas in the context of plasma medicine typically proceeds through a liquid layer covering exposed cells. The wounds and their liquid covering often have irregular shapes with electrical properties (i.e. conductivity and permittivities) that may differ not only from wound-to-wound but also for a single wound as healing proceeds. The differing shapes and electrical properties extend into the liquid within the wound that typically contains cellular materials such as blood platelets. The plasma, wound, liquid and intra-liquid cellular components represent an interacting system of mutual dependence. In this paper, we discuss the results from a computational investigation of the treatment of small, liquid-covered wounds by filamentary dielectric barrier discharges. The sizes of the wounds are of the order of the plasma filaments and the liquid within the wound, an approximation of blood serum, contains idealized blood platelets. We find that the electrical properties of a wound can have significant effects on the spreading of the plasma on its surface by virtue of the deformation of the vacuum electric fields due to the shape, the effective capacitance of the wound and the discontinuities in electrical permittivity. This in turn effects the penetration of the electric field to cells under the liquid. The orientation and permittivity of the platelets relative to the liquid determines the electric fields that may stimulate the platelets.

A second-order scheme for Maxwell's equations with dielectric permittivity discontinuities and total field-scattered field boundaries

A finite volume scheme for numerical solution of Maxwell's equations in regions with dielectric permittivity discontinuities and total field-scattered field (TFSF) boundaries is proposed. The scheme is second-order accurate in space and time. The key idea is to choose stencils for approximation of derivatives used to increase the order of approximation so that they do not cross dielectric permittivity discontinuities or TFSF boundaries. Computational results verify second order of approximation of the proposed scheme.

Dispersion relation for surface plasmon polaritons on a Schottky junction

The conventional analysis of surface plasmon modes on dielectric-metal interfaces requires clearly defining the permittivity discontinuity at the interface. A pivotal assumption of such an analysis is that the formation of the dielectric-metal interface does not change the material properties and the materials forming the interface have identical permittivities before and after the formation of the interface. However, this assumption breaks down if an interface is made between a metal and a semiconductor which is commonly known as a Schottky junction. Under certain conditions, such an interface can sustain a surface plasmon polariton (SPP) mode. It is also possible to change the properties of the media surrounding the Schottky junction interface by applying an external potential difference across the junction. Central to the understanding of the SPP mode behaviour in such a complex morphological interface is the dispersion relation which defines the feasible SPP modes and their characteristics. Here, we carry out a detailed analysis to derive an analytical expression for the dispersion relation for a Schottky junction. Our analysis takes into account the space charge layer formed due to the charge distribution across the Schottky junction and resulting new boundary conditions.

Optical waveguide grating couplers: 2nd-order and 4th-order finite-difference time-domain analysis

Output optical waveguide grating couplers are rigorously analyzed using the 2-order and the 4-order finite-difference time-domain (FDTD) method in conjunction with the total field/scattered field (TF-SF) approach and special averaging and regularization techniques for the mitigation of permittivity discontinuities. Volume-holographic and surface-relief grating couplers are analyzed for both TE and TM polarizations. The 2- and 4-order FDTD results are compared in terms of computational efficiency and accuracy. In addition, the FDTD results are compared to the approximate ones obtained by the rigorous coupled-wave analysis in conjunction with the leaky modes.

Finite-difference-time-domain analysis of finite-number-of-periods holographic and surface-relief gratings

The total-field-scattered-field formulation of the finite-difference time-domain method (FDTD) is used to analyze the diffraction of finite incident beams by finite-number-of-periods holographic and surface-relief gratings. Both second-order and fourth-order FDTD formulations are used with various averaging schemes to treat permittivity discontinuities and a comparative study is made with alternative numerical methods. The diffraction efficiencies for gratings of several periods and various beam sizes, for both TE and TM polarization cases, are calculated and the FDTD results are compared with the finite-difference frequency-domain (FDFD) method results in the case of holographic gratings, and with the boundary element method results in the case of surface-relief gratings. Furthermore, the convergence of the FDTD results to the rigorous coupled-wave analysis results is investigated as the number of grating periods and the incident beam size increase.

Investigation of 2-D electromagnetic transients in a circular cylinder with time discontinuity in permittivity via the resolvent method

The resolvent method approach is proposed for analytically solving the time domain Volterra integral equation (TDVIE) which describes the electromagnetic fields in 2-D cylindrical structures with time changes in the permittivity. It is shown that the approach allows investigation of the electromagnetic field transformation due to an abrupt time change in dielectric permittivity inside a circular cylinder as well as the construction of the Green’s function for an initial-boundary value problem. Key mechanisms of electromagnetic field transformation are investigated and a qualitative distinction of the processes is shown that depends on an initial field configuration.

Pressure-induced phase transition in soy oil

Following the earlier works [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998). R.M. Siegoczyński, J. Je¸drzejewski and R. Wiśniewski, High Pressure Res. 1 225–301 (1989).] on the investigation of oily liquids such as oleic and triolein, authors predicted the occurrence of a phase transition in the wide class of commercial oils containing oils with double carbon bonds. Those predictions have been confirmed by the observation of the phase transition in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, in press]. The present article shows further confirmation of those predictions presenting first-order phase transition in soy oil. The measurements performed in the range up to 1 GPa have shown pressure-related discontinuity of permittivity and volume.

Electromagnetic Forming by Distributed Forces in Magnetic and Nonmagnetic Materials

In this paper, we discuss the electromechanical force densities associated with pulsed electromagnetic fields in inhomogeneous, linear media with conductive losses, in the context of a process of shaping metal objects. We show that the conductivity and the gradients in permittivity and in permeability lead to volume forces, while jump discontinuities in permittivity and permeability lead to surface forces. These electromagnetic forces are assumed to act as volume (body) source densities in the elastodynamic equations and as surface source densities in the corresponding boundary conditions that govern the elastic motion of deformable matter. As an example, we apply the theory to the calculation of the elastic field in a hollow cylindrical object made of a conducting magnetic or nonmagnetic material. We compare the numerical results with those for the classical theory of elasticity with concentrated forces on the boundaries of the material as the source of the elastodynamic field.

Comparison of Cartesian grid configurations for application of the finite-difference time-domain method to electromagnetic scattering by dielectric particles.

Two grid configurations can be employed to implement the finite-difference time-domain (FDTD) technique in a Cartesian system. One configuration defines the electric and magnetic field components at the cell edges and cell-face centers, respectively, whereas the other reverses these definitions. These two grid configurations differ in terms of implication on the electromagnetic boundary conditions if the scatterer in the FDTD computation is a dielectric particle. The permittivity has an abrupt transition at the cell interface if the dielectric properties of two adjacent cells are not identical. Similarly, the discontinuity of permittivity is also observed at the edges of neighboring cells that are different in terms of their dielectric constants. We present two FDTD schemes for light scattering by dielectric particles to overcome the above-mentioned discontinuity on the basis of the electromagnetic boundary conditions for the two Cartesian grid configurations. We also present an empirical approach to accelerate the convergence of the discrete Fourier transform to obtain the field values in the frequency domain. As a new application of the FDTD method, we investigate the scattering properties of multibranched bullet-rosette ice crystals at both visible and thermal infrared wavelengths.

Efficient finite-difference time-domain scheme for light scattering by dielectric particles: application to aerosols

We have examined the Maxwell-Garnett, inverted Maxwell-Garnett, and Bruggeman rules for evaluation of the mean permittivity involving partially empty cells at particle surface in conjunction with the finite-difference time-domain (FDTD) computation. Sensitivity studies show that the inverted Maxwell-Garnett rule is the most effective in reducing the staircasing effect. The discontinuity of permittivity at the interface of free space and the particle medium can be minimized by use of an effective permittivity at the cell edges determined by the average of the permittivity values associated with adjacent cells. The efficiency of the FDTD computational program is further improved by use of a perfectly matched layer absorbing boundary condition and the appropriate coding technique. The accuracy of the FDTD method is assessed on the basis of a comparison of the FDTD and the Mie calculations for ice spheres. This program is then applied to light scattering by convex and concave aerosol particles. Comparisons of the scattering phase function for these types of aerosol with those for spheres and spheroids show substantial differences in backscattering directions. Finally, we illustrate that the FDTD method is robust and flexible in computing the scattering properties of particles with complex morphological configurations.

Numerical performance of finite-difference modal methods for the electromagnetic analysis of one-dimensional lamellar gratings

The numerical performance of a finite-difference modal method for the analysis of one-dimensional lamellar gratings in a classical mounting is studied. The method is simple and relies on first-order finite difference in the grating to solve the Maxwell differential equations. The finite-difference scheme incorporates three features that accelerate the convergence performance of the method: (1) The discrete permittivity is interpolated at the lamellar boundaries, (2) mesh points are located on the permittivity discontinuities, and (3) a nonuniform sampling with increased resolution is performed near the discontinuities. Although the performance achieved with the present method remains inferior to that achieved with up-to-date grating theories such as rigorous coupled-wave analysis with adaptive spatial resolution, it is found that the present method offers rather good performance for metallic gratings operating in the visible and near-infrared regions of the spectrum, especially for TM polarization.

Computation of the near-field pattern with the coupled-wave method for transverse magnetic polarization

In this paper, an accurate method for computing the elecromagnetic field distribution in lamellar gratings is proposed. The method that relies on the rigorous coupled-wave analysis provides accurate numerical results and avoids possible sources of artefacts due to permittivity discontinuities. Its performance is analysed through various lamellar grating cases, including dielectric and metallic materials, the visible and near-infrared (1–10 μm) regions of the spectrum. Special attention is placed on field singularities which are in general present at the grating wedges for transverse magnetic polarization.

Analysis of metal-interlaced-grating vertical-cavity surface-emitting lasers using the modal method by modal expansion

It is analyzed by the modal method by modal expansion (MMME) that the strong polarization discrimination of a vertical-cavity surface-emitting laser (VCSEL) can be effectively obtained by using the metal-interlaced grating on the topmost layer of the VCSEL. The MMME is used to overcome the problems coming from the large permittivity discontinuities at GaAs-Al-air-Al interfaces. The analyses predict the correct direction of dominant polarization and the mode-suppression ratio. The calculated transmission efficiencies explain the characteristics of the VCSEL's below threshold. It is found that the difference in phase and amplitude between the two orthogonal polarization generated by the grating plays important roles for the selection of a dominant polarization through mirror reflectivities and mirror losses. In addition, the influence of various thin metal layers on polarization stabilization is demonstrated.

Analytic solution of the forward problem for induced current electrical impedance tomography systems

An analytic method of solving the forward problem for a single target in a two-dimensional induced-current electrical impedance tomography (EIT) system is presented. The solution, derived for a single circular target anywhere within a circular region, takes account of both conductivity and permittivity discontinuities between target and background, and yields quadrature components of peripheral potential differences. The solution is used to explore the effects that the position and size of the target and its conductivity and permittivity have on the peripheral potential differences and the required instrumentation sensitivity to detect the target. It is shown that the effects of a change in target conductivity and permittivity are almost indistinguishable from those of a change in target area. It is also shown how the induced-current analytic solution may be modified to simulate an injected-current EIT system.

Time-domain study of arbitrary dipole in planar geometry with discontinuity in permittivity and permeability

Transient fields arising from a general impulsive dipole above ground characterized by permittivity and permeability are studied. A detailed analysis for arbitrary electric dipole excitation is given, and the fields arising from the analog magnetic sources can be obtained by applying the duality transform. The mathematical description of this problem is done using the Hertz vector, whose solution in the time domain is derived in a novel way using the exact image theory. From this solution, which involves a definite integral, the actual fields are obtained through simple differentiations. The efficiency of the method is demonstrated by solving 14 previously unknown closed-form results for various field components in certain specific cases. Seven of these are obtained for electric dipole excitation and listed, whereas the corresponding results in the case of magnetic excitation can be easily written by applying the duality transform. >