Dielectric Permittivity Profile Research Articles

Light-driven PT symmetry in colloids with gain and loss nanoparticles

We consider a planar layer of a colloid solution with gain and loss nanoparticles. The concentration of the particles of both types is assumed to provide balanced light amplification and dissipation in the corresponding effective medium. The normally incident plane electromagnetic wave causes the spatial separation of gain and loss particles due to the pulling and pushing ponderomotive forces that act on active and absorptive particles, respectively. We show that at the moderate intensity of incident light, the emerging stationary distribution of the gain and loss nanoparticles forms a parity–time (PT)-symmetric profile of the effective dielectric permittivity satisfying the condition εeff(−z)=εeff∗(z). The magnitude of the imaginary part of the colloid refractive index can be controlled by the intensity of incident light, which makes the proposed tunable PT-symmetric layer a promising tool for studying non-Hermitian optical phenomena.

Dispersion Equations of Transverse Electromagnetic Waves Narrowly Localized Near the Interface between the Media with Different Graded-Index Profiles

"Combinations of three pairs of contacting media with linear, exponential, and parabolic profiles of dielectric permittivity are described theoretically. Three new types of narrowly localized transverse electric waves propagating along the interfaces between the considered graded-index media are found. The exact dispersion equations for each type of the waves determining the effective refractive index in dependence on optical and geometric characteristics are obtained. The influence of the thicknesses of the graded-index layers on dispersion equation solutions is analyzed. It is found that the effective refractive index increases with an increase in the thickness of the gradedindex layers in all considered combinations of the contacting media. The thickness of the parabolic graded-index profile has the least significant effect on the effective refractive index, compared to the linear and exponential ones. "

Finding Infinities in Nanoconfined Geothermal Electrolyte Static Dielectric Properties and Implications on Ion Adsorption/Pairing.

Infinities should naturally occur in the dielectric responses of ionic solutions relevant to many geochemical, energy storage, and electrochemical applications at a strictly zero frequency. Using molecular dynamics simulations cross-referenced with coarse-grained Monte Carlo models, using nanoslit pore models at hydrothermal conditions, and treating confined mobile charges as polarization, we demonstrate the far reaching consequences. The dielectric permittivity profile perpendicular to the slit (ϵ⊥(z)) increases, not decreases, with ionic concentration, unlike in the more widely studied megahertz-to-gigahertz frequency range. In confined electrolytes, the divergences in ϵ⊥(z) correctly describe crossovers between bulk- and surface-dominated dielectric behavior. Nanoconfinement at low ionic concentrations changes monovalent ion energetics by 1-2 kJ/mol, but no dielectric property studied so far is universally correlated to ion adsorption or ion-ion interactions. We caution that infinities signal violation of the "electrical insulator" dielectric assumption.

Models of waveguides combining gradient and nonlinear optical layers

Objectives. Theoretical studies of the waveguide properties of interfaces between nonlinear optical and graded-index media are important for application in optoelectronics. Waveguides combining layers with different optical properties seem to be the most promising, since they can be matched to optimal characteristics using a wide range of control parameters. The paper aims to develop a theory of composite optically nonlinear gradedindex waveguides with an arbitrary profile, within which it is possible to obtain exact analytical expressions for surface waves and waveguide modes in an explicit form. The main feature of the theory proposed in this paper is its applicability for describing surface waves and waveguide modes, in which the field is concentrated inside the gradient layer and does not exceed its boundary, avoiding contact with the nonlinear layer.Methods. Analytical methods of the theory of optical waveguides and nonlinear optics are used.Results. A theoretical description of the waveguide properties of the interface between two media having significantly different optical characteristics is carried out. The formulated model of a plane waveguide is applicable to media having an arbitrary spatial permittivity profile. An analytical expression describing a surface wave propagating along the interface between a medium having stepwise nonlinearity and a gradient layer with an arbitrary permittivity profile is obtained. Additionally, analytical expressions for surface waves propagating along the interface between a medium with Kerr nonlinearity (both self-focusing and defocusing), as well as graded-index media characterized by exponential and linear permittivity profiles, are obtained.Conclusions. The proposed theory supports a visual description in an explicit analytical form of a narrowly localized light beam within such waveguides. It is shown that by combining different semiconductor crystals in a composite waveguide, it is possible to obtain a nonlinear optical layer on one side of the waveguide interface and a layer with a graded-index dielectric permittivity profile on the other.

Magnetoelectric coupling at microwave frequencies observed in bismuth ferrite-based multiferroics at room temperature

• Room-temperature single phase multiferroic materials was obtained • Magnetoelectric coupling was observed at microwave (GHz) frequency • The coupling suggests a dynamic interaction between magnetic moments and ferroelectric polarization 0.63Bi 0.99 La 0.01 Fe 1- x Mn x O 3 -0.33BaTiO 3 -0.04Na 0.5 Bi 0.5 TiO 3 ( x = 0.10, 0.15, and 0.20) ceramics have been prepared by solid state reaction, and their structural, ferroelectric, ferromagnetic, piezoelectric, and magnetoelectric properties are studied. Except for the x = 0.2 composition, the X-ray diffraction and SEM-EDX analysis on the sintered ceramics show that the samples are single-phase, rhombohedral perovskites at room temperature. The introduction of Mn ions leads to a small deterioration in the ferroelectric and piezoelectric properties, whilst the room-temperature magnetization increases upon doping. The optimal multiferroic properties are obtained for the x = 0.15 composition. The magnetoelectric coupling in this sample was evidenced by the anomalies occurring simultaneously in the dielectric permittivity and magnetic permeability spectral profiles in the microwave region. Such a coupled phenomenon can be attributed to a dynamic interaction between magnetic moments and ferroelectric polarization.

Single-slice microwave imaging of breast cancer by reverse time migration.

Microwave imaging of breast cancer is considered and a new microwave imaging prototype including the imaging algorithm, the antenna array, and the measurement configuration is presented. The prototype aims to project the geometrical features of the anomalies inside the breast to a single-slice image at the coronal plane depending on the complex dielectric permittivity variation among the tissues to aid the diagnosis. The imaging prototype uses a solid cylindrical dielectric platform, where a total of 24 optimized Vivaldi antennas are embedded inside to form a uniform circular antenna array. The center of the platform is carved to create a hollow part for placement of the breast and the multistatic, microwave scattering parameters are collected with the antenna array around the hollow center. The dielectric platform further enhances the microwave impedance matching against the breast fat tissue and preserves the vertical polarization during the measurements. In the imaging phase, a computationally efficient inverse electromagnetic scattering method-reverse time migration (RTM)-is considered and adapted in terms of scattering parameters to comply with the actualmeasurements. The prototype system is experimentally tested against tissue-mimicking breast phantoms with realistic dielectric permittivity profiles. The reconstructed single-slice images accurately determined the locations and the geometrical extents of the tumor phantoms. These experiments not only verified the microwave imaging prototype but also provided the first experimental results of the imagingalgorithm. The presented prototype system implementing the RTM method is capable of reconstructing single-slice, nonanatomical images, where the hotspots correspond to the geometrical projections of the anomalies inside the breast.

Sub-surface stratification and dielectric permittivity distribution at the Chang’E-4 landing site revealed by the lunar penetrating radar

Context.In 2019, China’s Chang’E-4 (CE-4) probe landed on the far side of the Moon: a first in lunar exploration. The Lunar Penetrating Radar (LPR) mounted on the Yutu-2 rover allows the mapping of the near-surface structure and the dielectric permittivity of the landing area. The dielectric properties of the lunar soil affect the propagation of the LPR signals, which can be used to infer the depth of sub-surface boundaries and derive the composition of the component materials.Aims.Our objectives are to estimate the fine-resolution spatial distribution of relative permittivity and to improve the interpretation of the geological processes combined with the radargram of the CE-4 landing area.Methods.We used a modified method that combines the F-K migration and the minimum entropy of the ground penetrating radar (GPR) signals to estimate the velocity and permittivity values; this has the advantage of obtaining the appropriate velocity and permittivity, even with the incomplete or unnoticeable hyperbolic curves in the radar imageResults.The sub-surface stratification of the CE-4 landing area is seen in the first 31 lunar days of the LPR data. A fine-resolution dielectric permittivity profile ranging from ~2.3 to ~6.3 is obtained with our method, and the actual depths of the observed prominent sub-surface interfaces are determined, giving a maximum average depth of ~38 m. The thickness of the regolith layer is in the range of ~5.7–15.6 m, with an average of 11.8 m. The permittivity of the near-surface regolith (<30 cm) is ~2.78 ± 0.01, the bulk density is 1.57 ± 0.01 g cm−3, which is close to the results of ~1.61 g cm−3at the Apollo 15 landing area. The permittivity map is consistent with the radargram; the regolith and the paleo-regolith layer have relatively low permittivity and low echo strengths, while the rock debris has high permittivity and shows strong echos in the radargram. Two buried craters of different diameters beneath the navigation sites 4–11 and 16–31 are revealed in the radar profile. The permittivity distribution map can show detailed variations of material properties both inside and outside craters.

Quasi-Newton-Based Inversion Method for Determining Complex Dielectric Permittivity of 3-D Inhomogeneous Objects

We present a new method for determining the complex dielectric permittivity profile of 3-D inhomogeneous dielectric objects from measurements of the scattered electric field vectors in the frequency domain. The method is formulated as a minimization of a cost function defined in terms of electric field integral equations known as the object and data equations. Instead of an unknown object function containing the electromagnetic parameters of the dielectrics, the contrast sources induced within the scatterers are designated as the unknowns of the inversion scheme to avoid solving the forward scattering problem at each step. Later, the minimization of the cost function is achieved via a limited-memory quasi-Newton scheme, based on the Broyden–Fletcher–Goldfarb–Shanno (BFGS) formula, which iteratively updates the Hessian matrix estimation. The numerical results with the simulated and experimental scattered electric fields demonstrate that the presented method is capable of reconstructing scatterers with complex shapes.

A frequency-independent inhomogeneous planar radome with high angular stability based on permittivity manipulating

In this paper, an inhomogeneous planar radome (IPR) has been thoroughly investigated from an electromagnetic perspective. The inhomogeneity is considered to be an exponential function. Closed-form expressions have been derived for the transmission and reflection coefficients. A radome with frequency-independent response and angular stability up to 53° is achieved by manipulating the dielectric Permittivity Profile Variation (PPV) function with definite curvature. Implementation has been done with the use of the equivalent material theory (EMT). The optimal radome wall is prototyped by perforating the host medium continuously (which eliminates losses due to the discretization). An ultra-wide-band (3–18 GHz) free space measurement setup is used to characterize the frequency response of this prototype. Measurements are performed for both polarizations of TE and TM and various angles of the incidence. The results are in good agreement with the unit-cell full-wave simulations. The design procedure is generally described, which can be implemented for various electromagnetic and mechanical requirements.

Flow monitoring by microwave imaging inside a cuboid cavity: Theory and numerical feasibility analysis

In this paper, we investigate multiphase flow monitoring inside metallic pipes by qualitative microwave imaging, where foreign objects inside the liquid flow are monitored to eliminate contamination. The motivation stems from the fact that conventional tomographic approaches of microwave imaging are inherently not suitable for real-time flow monitoring due to their computational requirements as these techniques aim to retrieve the dielectric permittivity profile inside the pipeline. In this context, we envision that the factorization method of qualitative inverse scattering theory, which is a shape retrieval algorithm from scattered field measurements, provides a better alternative for flow monitoring. To demonstrate the feasibility of such an approach, we first reformulate the factorization method by considering dyadic Green’s functions inside a cuboid cavity with perfectly conducting walls. Later, the formulation is simplified for a specific microwave measurement configuration to accelerate the reconstructions for real-time flow monitoring. Finally, flow monitoring is realized as a differential imaging procedure where foreign objects are detected by using differences of multi-static scattering parameters that are measured consecutively. The simulation studies performed for food and petroleum flows reveal the capabilities of the technique as a viable solution for different industrial flows.

Hydrogen bonding arrangement of ice II observed in interfacial water attached on hydrophobic and hydrophilic surfaces

Interfacial water dielectric permittivity and electric field profiles were probed and compared. Relative permittivity values between 3 and 4 were measured on both hydrophobic and hydrophilic substrates. Since ice has crystal structures responsible for many of the liquid water properties, Raman spectral lines of ice II were compared to the intramolecular vibrational spectrum of the interfacial air/water region. The coincidence of their spectral lines suggests that the interfacial air/water arrangement is similar to ice II and is induced by the interfacial electric field.

Effect of thermal profile on a shift in phase transition temperature of Sb-doped KNN piezoceramic

This work investigated the impact of the thermal profile in the shift of phase transition temperature for KNNS piezoceramic, using high-resolution synchrotron x-ray powder diffraction (SXPD) and dielectric measurement. The temperature-dependent dielectric permittivity and SXPD profile showed that all phase transformations occurred at higher temperature under heating than under cooling. Moreover, under cooling from 227 °C to −163 °C and reheating to 227 °C, none of the unit-cell volumes fully recovered to their initial size. These results suggest that the change in unit-cell volume under heating/cooling plays a significant role in the shift of phase transition temperatures that was observed.

Numerical‐analytical method for determining the dielectric constant of 1D inhomogeneous plate in a waveguide

The inverse diffraction problem is considered for a layered dielectric plate in a metal waveguide of arbitrary cross-section. The proposed solution is based on the Cauchy problem for the Riccati equation. Based on this solution, algorithm and code are developed for the dielectric permittivity profile reconstruction. The measured and mathematically simulated values of the complex reflection coefficient at finite number of frequencies are used as input data. Reconstructed dielectric permittivity profiles for layered plates are in good agreement with measured ones.

High gain, wide-angle QCTO-enabled modified Luneburg lens antenna with broadband anti-reflective layer

The gradient-index (GRIN) Luneburg lens antenna offers significant benefits, e.g. high aperture efficiency, low-power, minimal cost, wide beam scanning angle and broad bandwidth, over phased array antennas and reflector antennas. However, the spherical shape of the Luneburg lens geometry complicates the integration of standard planar feed sources and poses significant implementation challenge. To eliminate the feed mismatch problem, the quasi-conformal transformation optics (QCTO) method can be adopted to modify the lens’ spherical feed surface into a planar one. However, Luneburg lenses designed with QCTO method are limited to poor performance due to the presence of the reflections and beam broadening arising from the quasi-conformal mapping. In this paper, we present a new method of implementing QCTO-enabled modified Luneburg lens antenna by designing a broadband anti-reflective layer along with the modified lens’s planar excitation surface. The proposed anti-reflector layer is inherently broadband in nature, has a continuously tapered inhomogeneous dielectric permittivity profile along its thickness, and ensures broadband impedance matching. To show the new QCTO modified Luneburg lens antenna, an example lens antenna was designed at Ka-band (26–40 GHz) and fabricated using fused deposition modeling (FDM) based additive manufacturing technique. Electromagnetic performance of the lens antenna was experimentally demonstrated.

Polymorphic and morphotropic phase transitions in Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions

Study of evolution of ferroelectric correlations in a system which intrinsically exhibits short range polar order in the form of polar-nano regions (PNRs), is the goal of the present work. For this purpose, well-known Relaxor ferroelectric i.e. PbMg1/3Nb2/3O3(PMN) and its solid solutions with PbTiO3(PT) has been systemically synthesized by varying composition, precursors and synthesis parameters. Dynamics associated with the PNRs and structural phase transitions of various polymorphs have been traced through temperature and frequency dependent dielectric permittivity profile. Formation of solid solutions with PT generates ferroelectric correlations associated with the tetragonal polymorphs, suppresses thermal fluctuations, overcomes diffused character of phase transition, effects polarization switching, stabilizes ferroelectric hysteresis characteristics and shifts dielectric permittivity maxima toward higher temperatures. Addition of PT led to relaxation dynamics associated with the multiple polymorphic phase transitions for T < 500 K, where system exhibits intrinsic character. Polymorphs with low symmetries lies below freezing temperature, where structural phase transition generates polar order. Diffusivity and activation energy of phase transitions, and freezing temperatures of polar regions of various processes have been quantified and compared as a function of PT. Excellent ferroelectric response of the compositions lying in the vicinity of the Morphotropic phase boundary composition has been observed.

Characteristics of Electromagnetic Wave Absorption in Cylindrical Black Holes with Positive and Negative Refractive Indexes

The problem of plane electromagnetic wave scattering by cylindrical “black holes” with radial profile of dielectric permittivity and magnetic permability in the shell chosen in the form e(ρ) = μ(ρ) ~ 1/ρ2 and with constant permittivity and permeability in the central region is considered. The problem in rigorous formulation is solved both analytically for a basic model of the absorber and numerically using the one-dimensional method of finite elements for a modified model. The results obtained for absorption efficiency, radar cross-section, and field distribution in the cylinder are presented and discussed. It is shown that the absorption efficiency of the cylinder with negative refractive index at realistic values of parameters of the cylinder remains higher than the absorption efficiency of a similar cylinder with positive refractive index. However the indicated advantage is not so great as the advantage compared to the absorption efficiency of the black body predicted in the previous publications for the case of extremely low losses at the surface of the cylinder and extremely high magnitudes of negative permittivity and permeability and losses in the central region of radius approaching zero.

Mode-sorter design using continuous supersymmetric transformation.

We propose to use a continuous supersymmetric (SUSY) transformation of a dielectric permittivity profile in order to design a photonic mode sorter. The iso-spectrality of the SUSY transformation ensures that modes of the waveguide preserve their propagation constants while being spatially separated. This global matching of the propagation constants, in conjunction with the adiabatic modification of the refractive index landscape along the propagation direction, results in the negligible modal cross-talk and low scattering losses in the sorter. We show that a properly optimized SUSY mode sorter outperforms a standard asymmetric Y-splitter by reducing the cross-talk by at least two orders of magnitude. Moreover, the SUSY sorter is capable of sorting either transverse-electric or transverse-magnetic polarized modes and operates in a broad range of wavelengths. At the telecommunication wavelength, the 300-μm-long SUSY sorter provides the cross-talk of -35 dB and a broad operation bandwidth. The design proposed here paves the way toward efficient signal manipulation in integrated photonic devices.

Determination of the Porosity Distribution during an Erosion Test Using a Coaxial Line Cell.

The detection of porosity changes within a soil matrix caused by internal erosion is beneficial for a better understanding of the mechanisms that induce and maintain the erosion process. In this paper, an electromagnetic approach using Spatial Time Domain Reflectometry (STDR) and a transmission line model is proposed for this purpose. An original experimental setup consisting of a coaxial cell which acts as an electromagnetic waveguide was developed. It is connected to a transmitter/receiver device both measuring the transmitted and corresponding reflected electromagnetic pulses at the cell entrance. A gradient optimization method based on a computational model for simulating the wave propagation in a transmission line is applied in order to reconstruct the spatial distribution of the soil dielectric permittivity along the cell based on the measured signals and an inversion algorithm. The spatial distribution of the soil porosity is deduced from the dielectric permittivity profile by physically based mixing rules. Experiments were carried out with glass bead mixtures of known dielectric permittivity profiles and subsequently known spatial porosity distributions to validate and to optimize both, the proposed computational model and the inversion algorithm. Erosion experiments were carried out and porosity profiles determined with satisfying spatial resolution were obtained. The RMSE between measured and physically determined porosities varied among less than 3% to 6%. The measurement rate is sufficient to be able to capture the transient process of erosion in the experiments presented here.

Scattering of a Plane Electromagnetic Wave by a Multilayer Spherical Lens

We propose an analytical solution of the problem of diffraction of a plane electromagnetic wave by a multilayer dielectric (including plasmon) sphere. The solution is obtained using the method of separation of variables. New efficient recurrence relationships are obtained for calculations of the fields in layers, as well as formulas for the fields in the near and far diffraction zones. The novelty of the proposed solution is connected with the way of representing its radial part in the form of normalized functions. It is shown that as the number of the lens layers, which approximate the smooth profile of dielectric permittivity, grows, the electric field at the focusing point increases and reaches the maximum value. This allows one to determine the minimum required number of layers in practical problems. Resonance properties of metal-dielectric nanoparticles are studied in the optical band.

Response properties at the dynamic water/dichloroethane liquid–liquid interface

ABSTRACTWe present a novel approach for calculating the static dielectric permittivity profile of a liquid–liquid interface (LLI) from molecular dynamics simulations. To obtain well-defined features, comparable to those observed at solid–liquid interfaces, we find it essential to reference to the instantaneous liquid–liquid interface rather than the more commonly used average Gibbs interface. We provide a coarse-grained approach for the practical definition of the instantaneous interface and present numerical results for the prototypical water/1,2-dichloroethane system. These results show that the parallel components of the dielectric permittivity tensor can be accurately extracted. In contrast, the perpendicular component does not converge to the correct bulk value at large distances from the LLI, highlighting a flaw in the regularly applied coarse-graining procedure.