Effective Dielectric Constant Research Articles

Estimation the dielectric properties of solvation shells and nano-cavities by solvatochromic shift of organic dye

We investigated the preferential solvation effect of pyridinium-N-phenolate betaine (organic dye) taken as a molecular probe in two binary solvents (water-BuOH and water-BuNH2) in concentration range 0-100%. The Onsager-Liptay model was used to connect the spectral solvatochromic shift in solvation shell of the dye with the dielectric permittivity of the environment around its chromophore. That makes it possible to estimate the effective dielectric constant in the microscopic region of the probe, based on the values of the experimentally measured solvatochromic shifts. It was shown that the solvation shell of the dye is significantly depleted with the second component of binary solvent in water solution. It is true both for the water-BuOH and water-BuNH2 solvents. The absolute spectral shift in case of water-BuNH2 solvent is greater than in the second case. However, the relative depletion is stronger in case of water-BuOH. The innovative potential of the method is in the development the nanoprobe devices to measure the dielectric constant of small objects and nano-regions, to control instantaneous solvent concentration into evaporating sessile droplet of binary solvent in different zones of the droplet.

Design, analysis and fabrication of the CPW resonator loaded by DGS and MEMS capacitors

In this paper, an analytical method of resonant frequency, tuning range, the effective relative dielectric constant, and characteristic impedance is proposed, which is for coplanar waveguide (CPW) resonator loaded by defected ground structure (DGS) and micro-electromechanical systems (MEMS) capacitors. The analytical solution is achieved by an employing equivalent method. The resonant frequency, tuning range, and effective relative dielectric constant are obtained by the analytical solution. For verifying the effectiveness of the proposed method, a CPW tunable bandstop filter (BSF) with DGS and MEMS capacitors is designed, simulated, and fabricated, results show good effectiveness of the proposed analysis method. By changing the height of the MEMS beam with the actuation voltage, the designed BSF can switch the center frequency among three states (i.e. 18.5 GHz, 18.2 GHz, 17.5 GHz, respectively), and fractional bandwidth is changed as well (i.e. 37.8%, 45.6%, 49.5%, respectively).

SYNTHESIS AND CHARACTERIZATION OF (ZNO)–(CO3O4) NANOCOMPOSITE VIA SPRAY PYROLYSIS PROCESS: THE USE OF THE BRUGGEMAN MODEL ON OPTICAL PROPERTIES PREVISION

In the present paper, (ZnO)–(Co3O4) nanocomposite thin films have been prepared by using spray pyrolysis deposition on a glass substrate at 350∘C. After that, the as-obtained films have been characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the double beam UV-visible (UV-vis) spectrophotometer. Furthermore, the Bruggeman model is used to predict the evolution of the optical dielectric constant (real and imaginary parts: [Formula: see text] and [Formula: see text] to compare them with those obtained from the experimental results. The XRD pattern reveals that the nanocomposite film has diffraction peaks 2[Formula: see text], 36.95∘ corresponding respectively to the (220), (311) planes of cubic Co3O4 and another about of 2[Formula: see text] corresponding to the (101) plane of Wurtzite ZnO. Using the Debye Scherrer formula, the crystallite size of (ZnO)[Formula: see text]–(Co3O[Formula: see text] nanocomposite is found about 32[Formula: see text]nm, while the obtained thickness of this nanocomposite is about 780[Formula: see text]nm using the DekTak Stylus profilometer. Besides, the morphology analysis shows that the nanocomposite sample is well covered without holes and/or cracks and it has uniform dense grains. The evaluation of the transmittance, reflectance, refraction index, extinction coefficient, real and imaginary parts of dielectric constant as function of wavelength illustrates that the optical response of nanocomposite thin film (ZnO)[Formula: see text]–(Co3O[Formula: see text] depends on the influence of two mediums of pure materials ZnO and Co3O4 and their interaction. In addition, the direct band gap vs incident photon energy obtained from the Tauc plot equation shows that this nanocomposite has three values of band gap energy which are [Formula: see text][Formula: see text]eV, [Formula: see text][Formula: see text]eV (correspond to pure Co3O4 film) and [Formula: see text][Formula: see text]eV (correspond to pure ZnO film). Besides, the application of the Bruggeman equation indicates that the influence of the values of volume concentration and optical dielectric constant of the ingredient nanomaterials (ZnO and Co3O[Formula: see text] is significant on the value of the effective dielectric constant of nanocomposite thin film. The specific result of this study is the similarity between the spectra obtained from the Bruggeman model and the measured one, which proves that the application of this model is useful for the prediction of the optical properties of the composite.

Tuned dielectric and percolation behavior of cold-pressed polyvinyledene fluoride nanocomposites caused by Ni and BaTiO3 fillers

The dielectric and percolation behavior of polymer nanocomposites (PNC) comprising of polyvinylidene fluoride (PVDF)/nanocrystalline nickel (n-Ni) [conducting filler] and PVDF/n-BaTiO3 [ferroelectric insulating filler], prepared under the novel cold press method are compared. Higher effective dielectric constants (ɛeff) of 2400 and 400 at 40 Hz with volume fractions of filler fcon = 0.28 and $$f_{{{\text{BaTiO}}_{3} }} = 0.60$$ were observed, respectively. PVDF/n-Ni composites show percolation behavior associated with insulator to metal transition (IMT) at the percolation threshold (fc), while PVDF/n-BaTiO3 shows an effective electrical behavior due to the sum effect without showing any IMT. The drastic modulation in their dielectric, electrical and percolation behavior are attributed to the nature of filler present in them and has been explained by Percolation theory, Yamada model and VRH models. The universality and non-universality of exponents have been understood within the framework of the above models, the geometry of the fillers and the process conditions. Cold-pressed PNC based on ferroelectric filler are of superior quality for dielectric applications.

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.