Dielectric Inclusions Research Articles

An enhanced integral-equation formulation for accurate analysis of frequency-selective structures

In this work, a very efficient mixed-potential integral-equation formulation is implemented for the rigorous analysis of multilayered structures with arbitrarily shaped two-dimensional periodic metallic and/or dielectric inclusions. Original acceleration techniques have been developed for the computation of the components of the scalar and dyadic Green's functions, based on different types of asymptotic extractions according to the potential considered. The theoretical approach and its computational convenience have been validated through different full-wave analyses concerning both scattering problems and complex-mode dispersive behaviors in various frequency-selective structures for microwave applications.

Scattering of a pulsed wave by a sphere with an eccentric spherical inclusion

A dielectric sphere with an eccentric spherical dielectric inclusion and an incident amplitude-modulated plane electromagnetic wave constitute an exterior radiation problem, which is solved in this paper. A solution is obtained by combined use of the Fourier transform and the indirect-mode-matching method. The analysis yields a set of linear equations for the wave amplitudes of the frequency-domain expansion of the electric-field intensity within and outside the externally spherical inhomogeneous body; that set is solved by truncation and matrix inversion. The shape of the backscattered pulse in the time domain is determined by application of the inverse fast Fourier transform. Numerical results are shown for a pulse backscattered by an acrylic sphere that contains an eccentric spherical cavity. The effects of cavity position and size on pulse spreading and delay are discussed.

Birefringent nanostructured composite materials

We use a very efficient recursive method to calculate the effective optical response of materials made up of arbitrarily shaped dielectric inclusions arranged in periodic 2D arrays within a metal matrix with a lattice constant much smaller than the wavelength of the incident light, so that we may neglect retardation. The starting point of the calculation is a digitized image of the system. The geometrical shape of the inclusions and their orientation in the 2D array induce a birefringent optical response of the whole metamaterial that can be tailored to specific needs.

Inverse scattering in guides

We present statements and a method of solution to the inverse scattering problem of reconstructing permittivity of a dielectric inclusion in a 2D or 3D waveguide from the transmission characteristics. The approach employs a volume singular integral equation (VSIE) method. The unique solvability of VSIE is established. The inverse problem is solved by the method of iterations applied to VSIE; the convergence of the method is proved

Microwave absorption in the cores of the Abrikosov vortices pinned by artificial insulator inclusion

The spectrum of core excitations of the Abrikosov vortex pinned by a dielectric inclusion or nanoholes of the size of the coherence length is considered using the Bogoliubov–deGennes equations beyond the semiclassical approximation. While the lowest excitation, mini-gap, in the unpinned (or pinned by a metallic defect) vortex is of the order of Δ2/εF, it becomes of the order of the superconducting gap Δ. The reconstruction of the quasiparticle excitations’ spectrum has a significant impact on optical properties and on the tunneling density of states. We calculate the absorption amplitude and point out that, while in STM the energy gap ΔDOS is between a quasiparticles state with angular momentum μe=μs>1/2 and quasi-hole with μh=-μs the microwave absorption gap, Δdir is between states with μe=μh+1. It is shown that Δdir>ΔDOS. The large mini-gap might play a role in magneto-transport phenomena broadly associated with the “superconductor–insulator” transition in quasi 2D systems in which small insulating inclusions are generally present.

Tunable terahertz metamaterial based on resonant dielectric inclusions with disturbed Mie resonance

Tunable metamaterial operating in terahertz (THz) frequency range based on dielectric cubic particles with deposited conducting resonant strip was investigated. The frequency of the first magnetic type Mie resonance depends on the electric length of the strip. It can be changed under photoexcitation or applied voltage. This method of control was used for a design of tunable double negative metamaterial based on dielectric resonant inclusions and wire medium.

Microwave absorption in the cores of Abrikosov vortices pinned by artificial insulator inclusion

The spectrum of core excitations of the Abrikosov vortex pinned by a dielectric inclusion or nanoholes the size of the coherence length is considered using the Bogoliubov-deGennes equations beyond the semiclassical approximation. While the lowest excitation, minigap, in the unpinned (or pinned by a metallic defect) vortex is of the order of ${\ensuremath{\Delta}}^{2}/{E}_{F}$, it becomes of the order of the superconducting gap $\ensuremath{\Delta}$ (${E}_{F}$ is Fermi energy). The reconstruction of the quasiparticle excitations' spectrum has a significant impact on optical properties and on the tunneling density of states. We calculate the absorption amplitude and point out that, while in scanning tunneling microscopy the energy gap ${\ensuremath{\Delta}}_{\mathrm{DOS}}$ is between a quasiparticle state with angular momentum ${\ensuremath{\mu}}^{e}={\ensuremath{\mu}}_{0}g1/2$ and quasihole with ${\ensuremath{\mu}}^{h}=\ensuremath{-}{\ensuremath{\mu}}_{0}$, the microwave absorption gap, ${\ensuremath{\Delta}}_{\mathrm{dir}}$, is between the states with ${\ensuremath{\mu}}^{e}={\ensuremath{\mu}}^{h}\ifmmode\pm\else\textpm\fi{}1$. It is shown $\phantom{\rule{0.16em}{0ex}}$that ${\ensuremath{\Delta}}_{\mathrm{dir}}g{\ensuremath{\Delta}}_{\mathrm{DOS}}$. The large minigap might play a role in magneto-transport phenomena broadly associated with the ``superconductor-insulator'' transition in quasi-two-dimensional systems in which small insulating inclusions are generally present.

Influence of the inclusion shape on the conductivity of two-dimensional models of composites

The conductivity of some two-dimensional models of composites with randomly located and oriented dielectric inclusions of various shapes is considered. Exact analytical expressions are obtained for the effective conductivity σe at low concentration N of inclusions. The results are compared with the results of the corresponding computer experiment.

Control of electrostatic field localization in field-emission structures

Specific features of various methods used to increase the field-emission current of carbon-containing structures, which are intended to control the localization of electrostatic field on a micro-, nano-, and mesoscales, are considered. An original field-emission heterostructure is proposed in which the activation of the emitting layer of carbon nanotubes is ensured by incorporated dielectric inclusions. The mechanism of the electrostatic field localization in systems of this type is described. The efficiency of using mesoscale dielectric inclusions to develop technology for reliable, long-lived field electron emitters with increased current emissivity is justified.

Topological Derivative for Fast Imaging of Two-Dimensional Thin Dielectric Inclusions in The Wave Propagation Environment

In this paper, we consider the topological derivative concept for developing a fast imaging algorithm of thin inclusions with dielectric contrast with respect to an embedding homogeneous domain with a smooth boundary. The topological derivative is evaluated by applying asymptotic expansion formulas in the presence of small, perfectly conducting cracks. Through the careful derivation, we can design a one-iteration imaging algorithm by solving an adjoint problem. Numerical experiments verify that this algorithm is fast, effective, and stable.

EXPERIMENTAL STUDY ON A FLANGED PARALLEL-PLATE DIELECTRIC WAVEGUIDE PROBE FOR DETECTION OF BURIED INCLUSIONS

This paper presents an experimental study of a ∞anged parallel-plate dielectric waveguide (PPDW) probe for detecting dielectric inclusions in a dielectric host medium, with difierent electrical properties from the inclusions. The S-parameter signals from an inclusion (modelled as a conducting sphere) are shown to have resonant characteristics, from which the size and location of the inclusion can be deduced. As an example of a possible application for this technique, we use parameters of host medium and inclusions relevant for detection of tumors in body tissues. An experimental study was performed on solid tissue-simulating phantoms with embedded conducting dielectric inclusions. The measurements show promising results.

Three-dimensional numerical simulation of light field modulation in the vicinity of inclusions in silica subsurface

One of the important factors of the low laser induced damage threshold is the defects in the subsurface of fused silica. The three-dimensional model of a spherical inclusion in the subsurface is established in this study. Three-dimensional finite-difference time-domain method is used to calculate and simulate the light field distribution in the vicinity of inclusions. The effects of dielectric constant and inclusion size are analyzed, separately. The results show that the light intensity enhancement factor (LIEF) does not change with the size and the dielectric constant of the inclusions when the dielectric constant is smaller than that of fused silica, where the LIEF is kept at about 4. When the dielectric constant is 6.0, the LIEFs are 50.1588, 73.3904 and 102.9953 for the inclusions with sizes of 1.5λ, 2λ and 2.5λ respectively. When the inclusion size is constant, the LIEF will increase with the increase of dielectric constant. The light enhancement for the round inclusions is much higher than that for the ellipsoidal inclusions. Therefore, the round inclusions with large size and dielectric constant significantly enhance the electric field.

On the dielectric function tuning of random metal-dielectric nanocomposites for metamaterial applications

The potential of random metal-dielectric nanocomposites as constituent elements of metamaterial structures is explored. Classical effective medium theories indicate that these composites can provide a tunable negative dielectric function with small absorption losses. However, the tuning potential of real random composites is significantly lower than the one predicted by classical theories, due to the underestimation of the spectral range where topological resonances take place. This result suggests that a random mixture consisting of a metal matrix with embedded isolated dielectric inclusions is a promising design guideline for the fabrication of tunable composites for metamaterial purposes.

Existence and uniqueness of a solution to the inverse problem of the complex permittivity reconstruction of a dielectric body in a waveguide

This paper presents a statement, a proof of uniqueness, and a method of solution to the inverse problem of the determination of permittivity of a lossy dielectric inclusion in a three-dimensional waveguide of rectangular cross-section from the transmission characteristics. The approach is based on the solution to a volume singular integral equation (VSIE). The examination of this equation is based on the analysis of the corresponding boundary value problem (BVP) for the system of Maxwell's equations and the equivalence of this BVP and VSIE. The existence and uniqueness for VSIE in the space of square-integrable functions are proved. The permittivity reconstruction employs a method of iterations applied to the solution of VSIE.

Nanocomposite Phase-Change Memory Alloys for Very High Temperature Data Retention

Phase-change memory alloys based on germanium, antimony, and tellurium with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanophase dielectric inclusions are investigated for material and electrical properties. The new alloys are prepared by cosputtering with a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> target creating nanophase dielectric inclusions. The addition of the dielectric inclusions significantly increases the crystallization temperature without affecting the required programming current. In memory device configurations, the nanocomposite alloys exhibit a ten-year data retention above 200°C and a cycle life greater than 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cycles while maintaining the SET programming speed of 250 ns.

Tunable two-dimensional photonic crystal couplers made of dielectric elastomer inclusions

We propose a tunable directional coupler based on a two-dimensional photonic crystal made of dielectric elastomer rods embedded in air background. In the interaction region, the inclusions are a dielectric elastomer cylindrical actuator made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicon-made actuator and the coupling characteristics of the photonic crystal coupler are investigated. The coupling length of the photonic crystal coupler depends on the voltage applied between the electrodes, which is analyzed by the plane wave expansion method. Due to the radial strain of the dielectric elastomer under external voltage, the tunable photonic crystal coupler is realized. Numerical simulations obtained by the finite-difference time-domain method confirmed the feasibility of the tunable photonic crystal coupler.

On the imaging of thin dielectric inclusions buried within a half-space

Motivated from the application area of imaging of anti-personnel mines completely embedded in the homogeneous medium, the problem of non-iterative imaging of thin dielectric inclusions buried within a dielectric half-space is considered. For that purpose, an imaging algorithm operated at several frequencies is proposed. It is based on the asymptotic expansion formula of the scattering amplitude in the presence of the inclusions. Various numerical examples illustrate how the method behaves.

The effective dielectric constant of plasmas — A mean field theory built from the electromagnetic ionic T-matrix

This work aims to obtain the effective dielectric constant tensor of a warm plasma in the spirit of the derivation of a mixing law. The medium is made of non point-like ions immersed in an electron gas with usual conditions relating the various lengths which define the problem. In this paper the ion dielectric constants are taken from their RPA responses as developed in a previous paper [1]. Furthermore the treatment of the screening effects is made through a mathematical redefinition of the initial problem as proposed in Ref. [1]. Here the complete calculation of the T-matrix describing the scattering of an electromagnetic wave on an isolated ion immersed in an “effective medium” is given. It is used for building , in the spirit of a mixing law, a self-consistent effective medium theory for the plasma dielectric tensor. We then extend the results obtained in Ref. [1] to higher orders in ion or dielectric inclusion densities. The techniques presented are generic and can be used in areas such as elasticity, thermoelasticity, and piezoelectricity.

Simultaneously enhanced transmission and artificial optical activity in gold film perforated with chiral hole array

We propose a simple two-dimensional metallic periodic chiral structure (PCS) consisting of a dielectric substrate and a thin gold film perforated with gammadion-shaped chiral hole array, in which the transmittance and artificial optical activity can be simultaneously enhanced. The principle and optical performance of the PCS are demonstrated through the experimental realization of a PCS sample, from numerical design, fabrication, to optical characterization. Good agreement between theory and experiment has been obtained. The PCS sample shows an enhanced transmittance of 53% at wavelength 1168 nm, accompanied nearby by a polarization rotation peak with the effective specific rotatory power up to ${10}^{5}\text{ }\text{deg}/\text{mm}$. The enhancement mechanism of the dual effect is thoroughly studied by investigating the optical anomalies (i.e., Rayleigh anomalies, surface plasmon polaritons, and localized surface plasmons) in the PCS and their roles in the light-matter interaction. Several light-anomaly coupling regimes have been revealed. The single-layer metallic PCS is relatively easy to realize in optical frequencies by using mature microfabrication techniques such as electron-beam lithography and lift-off technique. The physical insight into the enhancement mechanism provides guidelines to develop more complicated PCS, such as multilayer PCS with metal and dielectric inclusions, which can produce stronger optical activity and better optical performance.

ON THE IMAGING OF THIN DIELECTRIC INCLUSIONS VIA TOPOLOGICAL DERIVATIVE CONCEPT

In this paper, we consider the imaging of thin dielectric inclusions completed embedded in the homogeneous domain. To image such inclusion from boundary measurements, topological derivation concept is adopted. For that purpose, an asymptotic expansion of the boundary perturbations that are due to the presence of a small inclusion is considered. Applying this formula, we can design only one iteration procedure for imaging of thin inclusions by means of solving adjoint problem. Various numerical experiments without and with some noise show how the proposed techniques behave.