Effective Dielectric Constant Research Articles

Microstructure evolution and mechanism of PLA/PVDF hybrid dielectrics fabricated under elongational flow

Polylactide (PLA)/polyvinylidene fluoride (PVDF) hybrid dielectrics with high melt flow index ratio have been prepared by a novel twin-eccentric rotor extruder (TERE). In TERE, the continuous elongational flow, originated from the alternate compression and release, plays a key role during melt blending. Compared to traditional shear flow, it facilitates the dispersion and orientation of the dispersed phase along the elongational direction, forming the fine and anisotropic micromorphology in PLA/PVDF blends. With the change of composition ratio, twice phase transitions and three structure regions are observed, in which the interpenetrating network structure is formed at 60-70 wt% PVDF loading. Based on the coupling effect of elongational flow and material properties, the mechanism of microstructure evolution for PLA/PVDF blends is put forward. In addition, the effective dielectric constant of PLA/PVDF blends is slowly and then rapidly improved in linear with PVDF content increasing. The turning point is the first phase transition due to the formation of new continuous phase of PVDF.

The lifetimes for each state of $$l=0$$ levels of the para-positronium

We developed a model for a para-positronium system by taking into account the annihilation condition which requires $$l=0$$ . A para-positronium system composed by an electron-antielectron pair is an unstable system that decays predominantly into two gamma photons via self-annihilation process. This is because of the conservation of (overall) charge conjugation parity. Our $$2+1$$ -dimensional model was based on an exact solution of a two-body Dirac–Coulomb type equation (one-time). The resulting non-perturbative spectra were found to have a form of quasi-normal modes that naturally give proper and damping oscillations of the system. As a result, with a single equation, not only the binding energies and total annihilation energy transmitted by the annihilation photons but also the lifetimes, $$\tau \left( n,\alpha \right) \propto n^{3}/\alpha ^{3}$$ , for each state of $$l=0$$ levels of the para-positronium were obtained. With this unique presentation of above-mentioned characteristic of the system, we also calculated transition frequencies and transition times between differing n level of $$l=0$$ . This also gave us an opportunity to discuss the screening effect from electronic environment of the system. For this, the effective dielectric constant of the medium that surrounds the annihilation point was adapted into the calculated non-perturbative spectra. This may provide an important tool for the positron annihilation lifetime spectroscopy studies and for development of related techniques.

Computation of Effective Properties of Graded and Layered Dielectrics

In this work, a finite element-based model is developed for the computation of effective dielectric constant and/or conductivity of single layer, multi-layered, and FGM composites. The computed values are validated against experimental data, and are seen to provide estimates better than all theoretical models. Thus, this computational model is expected to be useful in the design of new insulation systems.

The crystal and electronic structures, dynamical stabilities and thermal properties, elastic constants and mechanical stabilities, Born effective charges and dielectric constants of a novel tetragonal ZrO2 phase: First-principles calculations

Among six ZrO2 phases, the tetragonal ZrO2 with space group P42/nmc (D4h15, No. 137) (termed as t-ZrO2-I) has the largest average dielectric constant, but its highest elastic anisotropy easily makes a stress concentration and micro-crack and thus the lower mechanical strengths. In this paper, using first-principles calculations, we explore the crystal and electronic structures, dynamical stabilities and thermal properties, elastic constants and mechanical stabilities, Born effective charges and dielectric constants of a novel tetragonal ZrO2 with space group P42/mnm (D4h14, No. 136) (termed as t-ZrO2-II). The larger average dielectric constant, the higher yield, plastic and fracture strengths, the smaller elastic anisotropy and thus the smaller stress concentration and less micro-crack, the mechanical and dynamical stabilities show the novel t-ZrO2-II is a better dielectric and structural material than t-ZrO2-I reported previously.

Effect of nominal Indium substitution on structural, magnetic and microwave properties of Calcium-Barium M−type hexaferrites

A series of Indium doped Calcium-Barium M−type hexaferrite with nominal compositions Ca0.5Ba0.5Fe12-xO19Inx (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) was prepared by sol–gel method. The x-ray diffraction (XRD) analysis of the synthesized compositions revealed two phases; M−type hexaferrite phase as a main phase and α-Fe2O3 hematite phase. The gradual increasing trend in lattice parameters was observed on increasing Indium concentration showing incorporation of Indium in M−type hexagonal crystal structure. The grain size of M−type hexagonal phase was calculated using Debye–Scherer formula from non-overlapping peaks and it varied from 20 to 500 nm (0.5 μm). The scanning electron microscopy (SEM) micrographs showed hexagonal platelet-shaped, randomly distributed and agglomerated grains. The high resolution transmission electron microscopy (HRTEM) patterns further confirmed the observations of phases from x-ray diffraction (XRD). The remnant magnetization Mr and saturation magnetization Ms showed humped behaviour with maximum value for x = 0.25. The decrease in coercivity Hc was observed for x = 0.05 but it increased and remained nearly constant on further Indium addition. The effective dielectric constant showed resonance peaks at 4.3 and 8 GHz for all compositions and the effective loss decreases with frequency with maximum loss for x = 0.05, indicating the slight effect of In doping. The effective magnetic permeability showed small values and a resonance peak around 9 GHz, similarly magnetic losses also showed low values and a decreasing trend with frequency, not much noticeable influence of Indium doping was observed. These materials can be used in microwave frequency devices such as phase shifters and permanent magnets.

Meteorological Electromagnetics: Optical and Radar Measurements, Modeling, and Characterization of Snowflakes and Snow

We introduce the concepts, methodologies, and applications of meteorological electromagnetics with a focus on snow, which currently is the least understood component of the global water cycle. As "no two snowflakes are alike," the intricacies of snowflakes and snowfall are both truly fascinating and extremely challenging to measure, analyze, and predict. We describe a unique approach to the characterization of winter precipitation through the synergistic use of advanced optical instrumentation for in situ microphysical and geometrical measurements of ice and snow particles; image processing techniques to obtain the fall speed, size distribution, 3D shape (mesh), density, and effective dielectric constant of snowflakes; method of moments (MoM) scattering computations of precipitation particles; and state-of-the-art dualpolarization radars for the measurement of polarimetric scattering observables. We discuss the operations, observations, and analyses using this approach during a snow field campaign that took place in Colorado, United States, from 2014 to 2017, and we also introduce an international collaborative field program in association with the 2018 Winter Olympics in South Korea. One goal of this article is to promote meteorological electromagnetics as an interdisciplinary field where nature, science, and technology meet in some of the most fascinating and rewarding ways and where many key areas of interest and endeavors of the antennas and propagation community play an indispensable role.

Limit transitions in plane homogenization problems for two-phase dielectric composites with extreme material properties of one phase

The plane problem of calculating the effective dielectric constant of two-phase composite consisting of main material with one circular inclusion is considered. To solve the homogenization problem, the method of effective moduli with the support of the energy balance between the composite and the homogeneous comparison medium was used. In the solution obtained, the passage to the limit was made for the case of an inclusion with zero dielectric constant and for the case of a conductive inclusion. The limiting solutions are compared with the solutions of homogenization problems for a medium with a hollow and for a medium with a conducting inclusion boundary.

Synthesis of constructive-technological decisions of regulation of working capacitance of cables of industrial networks

Introduction. Over the past 10 years, the number of industrial networks has more than doubled. At the physical level, all industrial technology networks are based on twisted pair. Purpose. Synthesis of constructive-technological decisions of regulation of electric capacitance of the insulated conductor at a stage of manufacturing of twisted pair of cables of industrial networks. Methodology. The method of secondary charges to determine the capacitance of the insulated conductor by varying the thickness of the solid and foamed polyethylene insulation. Practical value. Effective regulation is provided on the basis of the obtained dependencies of the effective dielectric constant, the tangent of the dielectric loss angle and the capacitance of the insulated conductor on the degree of foaming and the thickness of the protective film of two-layer insulation. At a degree of porosity of 40 %, the dielectric constant decreases by 25 %, the tangent of the dielectric loss angle – by 33 %, the electrical capacitance of the insulated conductor – by 20 %.

Cation-Dependent Interfacial Structures and Kinetics for Outer-Sphere Electron-Transfer Reactions

The kinetics of aqueous outer-sphere electron-transfer (ET) reactions are determined in large part by noncovalent electrostatic interactions that originate from the surrounding electrolyte solution. In this work, we examine the role of spectator cations in modifying the rate of heterogeneous ET for an [Fe(CN)6]3–/[Fe(CN)6]4– redox pair. We combine the results of electrochemical measurement, in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), classical molecular dynamics simulation, and theoretical modeling to demonstrate how changing the identity of the spectator cation species over a series that includes Li+, Na+, K+, Rb+ to Cs+ influences the solvation properties and ET kinetics of the redox species. By analyzing the results in the context of the Marcus–Hush–Chidsey (MHC) theory, we find that the solvent reorganization energy increases systematically as the cationic radius decreases. The trend can be attributed to cation-dependent coordination environments of the redox species, whereby more cations of less charge density such as Cs+ than Li+ are present in the redox solvation shell in bulk and at the electrified interface, promoting weaker hydrogen bonds and lowering the effective interfacial static dielectric constant. We discuss the implications of these findings for enabling the tunability of reaction thermodynamics and rates in electrochemical processes.

Limits of the quasiharmonic approximation in MgO: Volume dependence of optical modes investigated by infrared reflectivity and ab initio calculations

Experimental and numerical investigation of phonon optical modes of MgO as a function of temperature (from 300 to 1400 K) and pressure (from 0 to 21 GPa) are here presented. Infrared reflectivity measurements were performed to probe energies and widths of the optical phonons, as well as of the multiphonon processes affecting the spectral shape, over a variation of the unit-cell volume exceeding 20%. Calculations within quasiharmonic approximation (QHA) account well for the volume dependence of the optical phonon energies observed in high-pressure experiments, while they fail at larger volumes, corresponding to the highest investigated temperatures. Moreover, QHA calculations more closely predict energies of transverse optical (TO) modes than those of longitudinal optical (LO) ones. This can be ascribed to known limitations in the modeling of the effective charges (${Z}^{*}$) and dielectric constant (${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$) that lead to an underestimation of the LO-TO splitting. Based on the comparison of our experimental and theoretical results, we propose an empirical analytical expression for ${{Z}^{*}}^{2}/{\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$ as a function of the atomic cell volume. Density-functional perturbation theory including phonon-phonon scattering up to the third order of the lattice potential expansion is used to calculate phonon widths. These calculations reproduce and explain remarkably well the nontrivial volume dependence of both TO and LO phonons linewidths determined by the experiments.

The structural, electronic, elastic, dielectric, dynamical, thermal and optical properties of Janus ZrOS monolayer: A first-principles investigation

The geometrical and electronic structures, elastic constants, dielectric permittivities, phonon spectra, thermal properties and optical responses of Janus ZrOS monolayer have been investigated by first-principles calculations. The lattice constant a, Zr–O bond length dZr-O, Zr–S bond length dZr-S, band gap Eg, in-plane stiffness C and Poisson's ratio υ of the Janus ZrOS monolayer are 3.44 Å, 2.15 Å, 2.55 Å, 1.88 eV, 226.35 N/m and 0.26, respectively. A p-d hybridized ionic bond exists in Janus ZrOS monolayer, instead of sp2 hybridized covalent bond in graphene. The larger values of Born effective charges Z11∗(Zr)=Z22∗(Zr)=6.76, Z11∗(O)=Z22∗(O)=-3.58 and Z11∗(S)=Z22∗(S)=-3.18 in-plane than the nominal chemical valences of +4 for Zr and −2 for O and S, reflecting a strong dynamic charge transfer from Zr atom to O and S atoms. After taking into account the Born effective charge and dielectric constant, the three acoustic-active modes (one A1 and two Eu) are degenerated (zero frequency) at Γ point, while a LO-TO splitting is observed for either Raman-active mode Eg or IR-active mode Eu at Γ point. The large dielectric permittivity, mechanical stability and dynamical stability make Janus ZrOS monolayer a promising dielectric material in modern semiconductor industry. The high and sharp absorption peaks in visible and UV light region propose Janus ZrOS monolayer a visible and UV light sensor application.

ADVANCED METHOD OF ANTENNA CALCULATION FOR RADIO MONITORING SYSTEMS OF ON-BOARD RADIO SOURCES

Analysis of the experience of modern armed struggle shows that timely detection of signals onboard radio sources by radio monitoring systems is an important task. One way to ensure its solution is the use of compact broadband antennas in the centimeter range. Therefore the development and improvement of methods for calculating broadband compact antennas in the centimeter wave range is an important and relevant scientific and practical task. An improved method for calculating a traveling wave antenna based on irregular symmetrical slit lines located arranged on a multilayer dielectric substrate (Vivaldi antennas) is proposed, by taking into account the thickness of the dielectric substrate, the relative effective dielectric constant of the substrate layers and two-way power supply to improve the directional properties of the antenna and its coordination in a given frequency band. In particular, the formulas of the phase multiplier of the system (for two radiating elements) and the resulting pattern of the antenna take into account the two-way power supply and the thickness and relative dielectric constant of the substrate. These advanced formulas for calculating and selecting these options antennas, lengths; maximum and minimum slot width; the coefficient of opening the gap; the width of the strip of symmetrical microstrip power line at the connection of the coaxial power line; the width of the strip at the intersection with the slit line; the width of the symmetrical slit line at the base of the opening; the length of a quarter-wave transformer based on a symmetrical microstrip line; the length of the symmetric microstrip power line; slit length; resonator diameter; the radius of the cover of the structural capacitor. The practical significance of the results obtained lies in the possibility of an approximate calculation of compact broadband antennas in the centimeter wavelength range. The results make it possible to model and manufacture these antennas for radio monitoring systems for onboard radio sources.

UGCPW Structure-Based Embedded Resonator with High Quality Factor for Microwave Substrate Characterization

In this paper, an ungrounded coplanar waveguide-based embedded resonator method for microwave substrate characterization was presented. The effective dielectric constant of the structure and the dielectric constant of microwave substrates can be calculated by the measured resonant frequency. The measured insertion losses at resonant frequencies and the 3 dB bandwidth can be used to determine the loaded and unloaded quality factors, including the dielectric quality factor which is related to dielectric loss tangent. The radiation loss and the extra length due to fringing effect caused by the open-end structure were taken into account to improve the extraction accuracy. The experimental unloaded quality factor of the proposed resonator at resonance order 1 reaches 211.3. The extracted dielectric constant and dielectric loss tangent of Taconic TLY at resonance order 1 are, respectively, 2.218 and 9.286×10−4, which are only 0.018 (relatively 0.82%) and 0.286×10−4 (relatively 3.18%) deviations from the datasheet values, respectively. The proposed resonator method is especially suitable for dielectric characterization of newly developed materials with the difficulty of realizing metal via holes, in which case substrate-integrated-waveguide (SIW) resonator methods are not applicable. When comparing with microstrip resonator methods, the proposed method is of higher quality factor, and it is more reliable and economical as well.

Эффективная диэлектрическая проницаемость композита с эллипсоидальными включениями в матричной оболочке

A composite material based on ellipsoidal inclusions distributed in a bonding medium is considered. A formula is obtained for calculating the effective dielectric constant of such a material, taking into account the presence of a layer of a binder on the inclusions, which prevents their direct contact. It is shown that the calculated values of the effective dielectric constant correspond to the experimental values for a composite based on sections of conductive fibers.

Preparation and characterization of Ni0.5Zn0.5Co0.2Fe1.8O4 filled polypropylene composites

This work discusses about the preparation and characterization of Ni0.5Zn0.5Co0.2Fe1.8O4 filled Poly Propylene Composites for microwave substrate applications. Phase pure Ni0.5Zn0.5Co0.2Fe1.8O4 filler composition is prepared through solid state ceramic route. Phase purity is confirmed by Powder X- ray diffraction analysis. Morphology and filler distribution of the composites are investigated by Scanning Electron Microscope analysis. Using Agilent 4294A Impedance Analyzer the dielectric and magnetic characterizations are done at low frequency region. Effective permeability and permittivity of the composites are compared with predicted values from different theoretical modeling approaches. Ni0.5Zn0.5Co0.2Fe1.8O4 filled PP composite have an effective dielectric constant of 6.75 and loss tangent of 0.006 at the optimum filler loading at 1 MHz. The composite also has magnetic permeability of 3.51 at the optimum filler loading. Relatively good dielectric constant, better relative permeability together with very low loss tangent make the Ni0.5Zn0.5Co0.2Fe1.8O4 filled PP Composites an excellent choice as Microwave substrate.

Избирательная сольватация красителя 4-DASPI в бинарном растворителе вода-этиленгликоль

Solvatochromic shifts of the absorption spectra maxima of the dye 4-DASPI (4- [4- (dimethylamino) styryl] -1-methylpyridinium iodide) in a binary solvent water-ethyleneglycol in the concentration range 0-100% were experimentally investigated. The dependence of the solvatochromic shift on the macroscopic dielectric constant of the solution and the concentration of ethyleneglycol was determined. The Onsager-Liptay model was used for the theoretical interpretation of the experimental data. It made it possible to estimate the effective dielectric constant in the microscopic area that contacts with dye chromophore taking into account the measured solvatochromic shifts. It was found that the value of the dielectric constant in the solvation shell of this dye differs significantly from the macroscopic value. The solvation shell is significantly enriched by ethyleneglycol (preferential solvation) over the components’ concentration range. The enrichment reaches its maximum approximately in the middle of this range. The composition of the dye solvation shell at different concentration is discussed.

A conformal symplectic multi-resolution time-domain method with ADE-PML

In this paper, the conformal finite-difference time-domain (CFDTD) technique and the concept of effective dielectric constant are applied to symplectic multi-resolution time-domain (SMRTD) algorithm based on Daubechies scaling functions, resulting in a conformal SMRTD (C-SMRTD) method. Moreover, a novel implementation of perfect matched layer with auxiliary differential equation (ADE-PML) is presented for the SMRTD method. Numerical results of the radar cross section (RCS) of a dielectric sphere verify the effectiveness of the C-SMRTD method, which shows good agreement with the results derived by analytical methods. It is also shown that the accuracy of the C-SMRTD method has been significantly improved compared with the MRTD method with step approximation, and the proposed method has an advantage over CFDTD at saving the CPU time and memory. Furthermore, a vault-top tunnel model is established with the proposed method, and the characteristic of the field cross-section distribution of the electromagnetic pulse (EMP) propagation in the tunnel model is also presented and discussed.

Comparative analysis of Luneberg spherical lens designs

Formulation of the problem. The development of modern mobile satellite communication systems dictates the need for the development of multipath antennas having: high values of the directional coefficient, low level of side lobes, a large number of scanning beams in a wide viewing sector without distortion in the azimuthal and angular planes. Multipath antenna systems based on spherical Luneberg lenses have these advantages. Despite their advantages, the spherical lenses of Luneberg did not find wide practical use due to the complexity of the design, the high cost of production, and the large mass (in some cases). Thanks to the progress in the field of artificial media, the emergence of new production methods, various designs of spherical Luneberg lenses have been developed. The use of artificial dielectrics allows you to create inexpensive, lightweight spherical Luneberg lenses. One widely used method of creating an artificial environment is to use partial air filling dielectrics. Luneberg lenses based on such media can have various designs: based on a dielectric ball with radial holes of variable diameter, from electrically small dielectric cubes of variable size, from a set of perforated dielectric disks, etc. For the manufacture of such lenses, various manufacturing technologies can be used, for example, three-dimensional printing, CNC machine. Purpose. Comparative analysis of the characteristics of two structures of the spherical Luneberg lens with the aim of working at frequencies above 9 GHz: from a set of perforated dielectric disks, from dielectric cubes of different sizes. Results. The results of comparative analysis of two designs of the spherical Luneberg lens are presented. The procedure of synthesis of each structure is considered. Design dependencies of effective dielectric constant used in development of investigated spherical lenses of Luneberg are given. Possible methods of technical implementation for each lens are considered, as well as important features that should be taken into account when designing and technical implementation. The weight of each structure was estimated. Conclusions about mechanical strength were made. Based on numerical modeling using the Weyland method, a comparison of directional properties in a wide frequency band was made. Conclusions have been drawn about the similarity and difference in directional characteristics. Practical importance. The scientific and technical results obtained in the article will be useful in choosing the design of the Luneberg lens from artificial dielectrics, depending on the specified technical requirements, and production conditions.

Effective strategies for reduced dielectric loss in ceramic/ polymer nanocomposite film

A novel approach is explored by mixing a giant dielectric constant ceramic powder CaCu3Ti4O12 (CCTO) with varying concentrations of polyvinylidene fluoride (PVDF). The CCTO/PVDF nanocomposite films were synthesized through the hot-press method. We found a high dielectric constant (~142) for 40 vol% PVDF content in CCTO/PVDF nanocomposite film. The effective medium theory predicted the theoretical value of effective dielectric constant of CCTO/PVDF nanocomposite film, which is best fitted with experimental data. We report a very low value of dielectric loss (~0.027) for 70 vol% PVDF content in CCTO/PVDF nanocomposite film, which is due to the formation of β phase of PVDF in the samples. The formation of β phase of PVDF is confirmed by the fibril structure.

A theoretical proposal for a plasma density sensor based on the dielectric substrate antenna with high dielectric constant

ABSTRACT With the rapid development of industrial production and aerospace, how to measure the plasma density has also developed rapidly. So a radio-frequency plasma transducer based on a three-layer dielectric substrate antenna with a high dielectric constant is introduced. The top and bottom layers are dielectric plates, which protect the internal antenna structure and improve the equivalent permittivity of the antenna. The middle layer is the structure layer of the designed antenna. And the antenna size is 3.8 × 2 × 1.8 mm3. When the plasma frequency changes from 0.3 GHz to 7 GHz, the corresponding dielectric substrate antenna resonant frequency (RF) changes from 4.076 to 5.213 GHz. The minimum unit is 0.1 GHz, and all the measurement accuracy is more than 90%. The method based on the effective dielectric constant of plasma will change under different plasma frequencies, so the RF of the antenna is different. In this paper, the radio-frequency plasma transducer is studied theoretically and analyzed numerically.