Changes In Dielectric Permittivity Research Articles

Coulomb Green’s function and image potential near a cylindrical diffuse interface

In a preceding paper [Comput. Phys. Commun. 184 (1): 51–59, 2013], we revisited the problem of calculating Coulomb Green’s function and image potential near a planar diffuse interface within which the dielectric permittivity of the inhomogeneous medium changes continuously along one Cartesian direction in a transition layer between two dissimilar dielectric materials. In the present paper, we consider a cylindrical diffuse interface within which the dielectric permittivity changes continuously along the radial direction instead. First we propose a specific cylindrical diffuse interface model, termed the quasi-harmonic diffuse interface model, that can admit analytical solution for the Green’s function in terms of the modified Bessel functions. Then and more importantly we develop a robust numerical method for building Green’s functions for any cylindrical diffuse interface models. The main idea of the numerical method is, after dividing a diffuse interface into multiple sublayers, to approximate the dielectric permittivity profile in each one of the sublayers by one of the quasi-harmonic functional form rather than simply by a constant value as one would normally do. Next we describe how to efficiently compute well-behaved ratios, products, and logarithmic derivatives of the modified Bessel functions so as to avoid direct evaluations of individual modified Bessel functions in our formulations. Finally we conduct numerical experiments to show the effectiveness of the quasi-harmonic diffuse interface model in overcoming the divergence of the image potential, to validate the numerical method in terms of its accuracy and convergence, and to demonstrate its capability for computing Green’s functions for any cylindrical diffuse interface models.

The physical and chemical properties of gamma ray irradiated polymer electrolyte films

The physical and chemical properties of Gamma ray irradiated polymer electrolyte (PEO-CdCl2) films have been investigated. The FT-IR result evidenced the degradation due to chain scission/cross linking in the irradiated films. The DSC and TGA results show that thermal stability and crystallinity are significantly decreased in irradiated films. The optical micrograph image shows the size of spherulite structure and surface roughness found to be decreased with increasing the irradiation dose. The increase in the optical absorption and shifts toward higher wavelength side was observed in the irradiated film. Also optical band gaps (Eg), Urbach energy is estimated and found to be decreased, meanwhile the number of carbon atoms in cluster increased with the dose. The changes of dielectric permittivity, AC conductivity and optical band gap after irradiation were attributed due to degradation. The high conductivity of 1.156×10−4Scm−1 observed in the 150kGy irradiated film; it was about to order magnitudes higher than that of non-irradiated film. The electric modulus results were depicts the relaxation time (τ) found decreased and broadening of peaks signifies it is the Non-Debye relaxation behavior. These obtained results reveal that there is a possibility of improving physical properties polymer electrolyte and it may open up various opportunities to use these materials in different applications.

Cellulose acetate–lithium bis(trifluoromethanesulfonyl)imide solid polymer electrolyte: ATR-FTIR and ionic conductivity behavior

Solid polymer electrolytes (SPEs) based on cellulose acetate (CA) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are prepared by solution cast technique. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy of the polymer salt complexes are recorded in the frequency range between 400 cm-1 and 4000 cm-1. The shifting of carbonyl band ( C=O ) at 1737 cm-1 to a lower wavenumber confirms the occurrence of complexation between the polymer and the salt. The electrochemical impedance spectroscopy (EIS) analysis discovered that the film with 25 wt.% of salt shows the highest ionic conductivity at room temperature. The change in real dielectric permittivity (εr) as a function of frequency at different salt concentrations which exhibits a dispersive behavior at low frequencies and decays at higher frequencies, shows the electrode polarization and space charge effect. The real modulus formalism (Mr) analysis shows that the polymer electrolytes in this work are ionic conductors.

Gigantic Optical Nonlinearity: Laser-Induced Change of Dielectric Permittivity of the Order of Unity

A possibility to tune optical properties of materials on demand is of great importance to both fundamental science and applications. We show that nanosecond laser pumping can significantly depopulate the ground state of AF455 dye nanoparticles, resulting in gigantic change of dielectric permittivity of the order of unity. Such extreme nonlinearity (χ(3) = 1.3 × 10–5 esu), evidenced by increase of the Mie scattering efficiency, places AF455 dye among the most efficient χ(3) nonlinear optical materials, extends the limits of active metamaterials and plasmonics, and paves the way to ultimate control of photonic devices and systems.

Phase transition and enhanced magneto-dielectric response in BiFeO3-DyMnO3 multiferroics

We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO3-x DyMnO3 (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H = 2 T for x = 0.2.

Rabi oscillations and stimulated mode conversion on the subwavelength scale.

We study stimulated mode conversion and dynamics of Rabi-like oscillations of weights of guided modes in deeply subwavelength guiding structures, whose dielectric permittivity changes periodically in the direction of light propagation. We show that despite strong localization of the fields of eigenmodes on the scales below the wavelength of light, even weak longitudinal modulation couples modes of selected parity and causes periodic energy exchange between them, thereby opening the way for controllable transformation of the internal structure of subwavelength beams. The effect is reminiscent of Rabi oscillations in multilevel quantum systems subjected to the action of periodic external fields. By using rigorous numerical solution of the full set of the Maxwell's equations, we show that the effect takes place not only in purely dielectric, but also in metallic-dielectric structures, despite the energy dissipation inherent to the plasmonic waveguides. The stimulated conversion of subwavelength light modes is possible in both linear and nonlinear regimes.

Ferroelastoelectric phase transition in (NH4)2CuCl4·2H2O single crystal

The (NH4)2CuCl4·2H2O crystal exhibits anomalous thermal, piezoelectric, dielectric and elastic properties in the vicinity of the ferroelastoelectric phase transition at TC = 200 K. Macroscopic order parameter is the h36 component of the spontaneous piezoelectric tensor connecting polarisation P3 and strain η6. The temperature change in h36 component was proportional to (TC − T)α, where α = 0.58 ± 0.05. Close to TC changes in dielectric permittivity were negligible. High value of ac conductivity in the high-temperature phase results from protons jumping between disordered ions NH4+ and between molecules of crystallisation water. Only longitudinal ultrasonic waves exhibited an abrupt change upon the phase transition. The relaxation time of the order parameter was determined from anomalous changes in attenuation of the longitudinal waves.

Highly stretchable dielectric elastomer material based on acrylonitrile butadiene rubber

This study presents a highly stretchable dielectric elastomer material for transducers based on acrylonitrile butadiene rubber (NBR). The material has advantages in that its mechanical and electrical properties can be modified according to the requirements of applications by changing the content of additives such as carbon black (CB), multi-walled carbon nanotubes (MWCNT), and graphite (GP) in the NBR matrix. First, the changes of dielectric permittivity depending on the additives are discussed. Moreover, the electrical resistance is examined in detail by changing the compositions of the additives, and the applicability of the material to the electrodes of transducers is investigated. Finally, the optimal contents of additives for actuators or sensors are discussed.

Comparison of photonic bandgaps of two-dimensional periodic and quasi-periodic photonic crystals with different relative permittivity dielectric

Photonic bandgaps (PBGs) of two-dimensional (2D) triangular-lattice and square-lattice and decagonal quasi-periodic photonic crystals (PCs) have been analyzed, with a given scatterer radius and dielectric relative permittivity changing from 1 to 30 within air-cylinders-in-dielectric and dielectric-cylinders-in-air constructions. The results have shown that 2D quasi-periodic PC is more likely to generate PBG and complete PBG than 2D periodic PC. For the given scatterer radius and two constructions, PBG widths of the two types of 2D PCs vary little, whereas the corresponding center frequencies decrease in smooth “hyperbola-like” curves with dielectric relative permittivity increasing monotonically. The present results will guide the design of PBG-type microstructure photonic devices.

Nonlinear dielectric effect in supercritical diethyl ether.

Nonlinear dielectric effect (NDE) describes changes of dielectric permittivity induced by a strong electric field in a liquid dielectric. The most classical finding related to this magnitude is the negative sign of NDE in liquid diethyl ether (DEE), recalled by Peter Debye in his Nobel Prize lecture. This article shows that the positive sign of NDE in DEE is also possible, in the supercritical domain. Moreover, NDE on approaching the gas-liquid critical point exhibits a unique critical effect described by the critical exponent ψ ≈ 0.4 close to critical temperature (T(C)) and ψ ≈ 0.6 remote from T(C). This can be linked to the emergence of the mean-field behavior in the immediate vicinity of T(C), contrary to the typical pattern observed for critical phenomena. The multi-frequency mode of NDE measurements made it possible to estimate the evolution of lifetime of critical fluctuations. The new way of data analysis made it possible to describe the critical effect without a knowledge of the non-critical background contribution in prior.

Investigating the performance and properties of dielectric elastomer actuators as a potential means to actuate origami structures

Origami engineering aims to combine origami principles with advanced materials to yield active origami shapes, which fold and unfold in response to external stimuli. This paper explores the potential and limitations of dielectric elastomers (DEs) as the enabling material in active origami engineering. DEs are compliant materials in which the coupled electro-mechanical actuation takes advantage of their low modulus and high breakdown strength. Until recently, prestraining of relatively thick DE materials was necessary in order to achieve the high electric fields needed to trigger electrostatic actuation without inducing a dielectric breakdown. Although prestrain improves the breakdown strength of the DE films and reduces the voltage required for actuation, the need for a solid frame to retain the prestrain state is a limitation for the practical implementation of DEs, especially for active origami structures. However, the recent availability of thinner DE materials (50 μm, 130 μm, 260 μm) has made DEs a likely medium for active origami. In this work, the folding and unfolding of DE multilayered structures, along with the realization of origami-inspired 3D shapes, are explored. In addition, an exhaustive study on the fundamentals of DE actuation is done by directly investigating the thickness actuation mechanism and comparing their performance using different electrode types. Finally, changes in dielectric permittivity as a function of strain, electrode type and applied electric field are assessed and analyzed. These fundamental studies are key to obtaining more dramatic folding and to realizing active origami structures using DE materials.

Temperature changes of dielectric permittivity and relaxation in aqueous lithium iodide solutions

The complex permittivity of aqueous LiI solutions is studied over a wide range of concentrations at temperatures of 288–323 K in the water permittivity dispersion region at seven frequencies in the range of 7.5–25 GHz. One relaxation region describable by the Debye or Cole-Cole equation is observed in these solutions. Dielectric relaxation time τ and static permittivity ɛs are studied as dependent on temperature and concentration. The time and enthalpy of activation of dielectric relaxation decrease in going from water to solutions, which corresponds to the distortion of the initial water structure and the increasing mobility of water molecules in hydration shells of ions. In the initial concentration range, the water activity is a linear function of 1/ɛs. The negative temperature dependence of ɛs disappears in going to concentrated solutions. At high concentrations, the static dielectric constant increases in response to increasing temperature. The new trends in ɛs and τ at elevated temperatures of 313–323 K are due to the formation of ion pairs and other ion-water groups having high dipole moments.

Superior magnetic, dielectric, and magnetodielectric effects in graphene/ZnCo2O4 nanocomposites

Although intensive research on spinel nanostructures has already been carried out, ZnCo2O4 is comparatively a less studied material because of its poor magnetic and dielectric properties. To focus ZnCo2O4 as a promising material with superior magnetic and dielectric properties in the present work, 2-dimentional nanosheets of ZnCo2O4 were synthesized using the large graphene surface as a template. Strong ferromagnetic behavior with asymmetries in coercivities is observed at room temperature. This was ascribed to the presence of Co2+ and Co3+ ions in ZnCo2O4 which gave rise to uncompensated spins due to a superexchange interaction. The nanocomposites containing large interfaces between graphene and ZnCo2O4 nanosheets exhibited unusual dielectric response due to trap states and superior magnetodielectric effect with an 18% change in dielectric permittivity for an applied magnetic field of 2.0 T as a result of combined effect between the Maxwell-Wagner polarization at the interface and a negative magnetoresistance of the ZnCo2O4 phase.

The effect of fast and continuous change of dielectric permittivity on whispering gallery modes in circular microcavity

The detailed analysis of the response of whispering gallery mode (WGM) to the permittivity change in circular microcavities made of materials with noteworthy relaxation time is presented. Continuous and mathematically well behavior function is employed to describe temporal change of resonator permittivity and the wave equation in both frequency and time domains is analyzed by means of inverse Laplace transform method. The exact transient response of cavity resonance mode with the steady state solutions are described carefully and it is shown that fast and continuous change of resonator dielectric permittivity behave like several propagating boundaries inside and outside the cavity. The transformed WGM appears after transient duration. These analyses are providing suitable tools for investigation of dynamic optical devices.

Experimental evaluation of agricultural biomass flow sensing behaviour using capacitive technique

To enhance industry control quality level as well as uphold enterprise economic benefit precise sensing and measurement of biomass flow is a major concern among researchers worldwide. Keeping in mind the shortcomings of existing sensing technologies this paper has developed a capacitive sensing method by making use of aop amp based bridge circuit along with particularly designed sensing electrodes. The objective of this work is fulfilled via experimental validation through a prototype hardware implementation of a flow sensing set up. The experimental results have specified the measurement system which is able to sense flow variation as a change of dielectric permittivity of different biomass materials under room condition. Moreover, the obtained results have revealed distinctive features clearly signifying the shapes and physical characteristics of electrodes, locations of the mounted electrodes on test pipe wall, dielectric permittivity and characteristics of test biomass materials.

Manifestation of ion specificity in the behavior of the dynamic dielectric permittivity of aqueous solutions of alkali metal halides

Dispersions of the refractive index are measured in aqueous solutions of potassium halides at different salt concentrations and temperatures of the solutions. The specific effect of anions on the dynamic dielectric permittivity of the solutions is found. A model is proposed to evaluate the character of changes in the dynamic dielectric permittivity of the solutions and effective dynamic polarizabilities of ions in the solutions based on the data about the dispersion of refractive indices. The role of ion sizes and the character of their interaction with a solvent in the manifestation of specific ion effects are discussed.

GPR utilization in artificial freezing engineering

To utilize ground penetrating radar (GPR) in artificial freezing engineering (AFE), the electromagnetic parameters (EMP) of frozen soil were measured using a vector network analyser, which showed that the dielectric permittivity and electric conductivity change abruptly at the boundary between the frozen and the non-frozen soil. Then similarity criteria of GPR model experiments were deduced, and GPR laboratory model experiments and field explorations of AFE were carried out. It was found that for AFE, the GPR travel time and profile characters of anomalies in model experiments were similar to those in field explorations, while the amplitude of GPR signals in laboratory model experiments were much stronger than those in field explorations. Numerical simulations were also implemented to analyse the relationship between model experiments and field explorations, which further told us why we could easily find the targets by GPR in the laboratory but not in field explorations. The outputs showed that GPR could be used to detect the thickness of the frozen wall and to find unfrozen soil defects, even though the amplitude of the reflective signals were much weaker than those of laboratory experiments. The research findings have an important theoretical value for AFE and permafrost region engineering, and the deduced GPR similarity criteria could be widely used in other GPR model experiments.

Dielectric Permittivity of Porous Si for Use as Substrate Material in Si-Integrated RF Devices

Dielectric permittivity of porous Si (PSi) layers formed on a low-resistivity p-type Si (0.001-0.005 Ω.cm) is thoroughly investigated using analytical expressions within the frame of broadband transmission line characterization method in the frequency range 1-40 GHz. It is demonstrated that the value of Si resistivity is critical for the resulting PSi layer permittivity even within the above limited resistivity range. The real part of PSi dielectric permittivity changes monotonically between 1.8 and 4 by changing the Si resistivity between 0.001 and 0.005 Ω.cm. The above study was made for porosities between 70% and 84%. The quality factor and attenuation loss of the investigated coplanar waveguide transmission lines were found to be Q=26 and a=0.19ndB/mm, respectively, at 40 GHz. These values are competitive to those obtained on quartz, which is one of the off-chip RF substrates with the lowest losses. This confirms the superiority of the PSi material, mentioned above, for use as a local substrate for the on-chip RF device integration.

Manifestation of ion specificity in the behavior of the dynamic dielectric permittivity of aqueous solutions of alkali metal halides

Dispersions of the refractive index are measured in aqueous solutions of potassium halides at different salt concentrations and temperatures of the solutions. The specific effect of anions on the dynamic dielectric permittivity of the solutions is found. A model is proposed to evaluate the character of changes in the dynamic dielectric permittivity of the solutions and effective dynamic polarizabilities of ions in the solutions based on the data about the dispersion of refractive indices. The role of ion sizes and the character of their interaction with a solvent in the manifestation of specific ion effects are discussed.

Magnetodielectric response of coexisting phases in half doped manganites

The magnetic field dependence of dielectric permittivity and resistivity has been measured simultaneously in two separate half doped manganites Pr0.75Na0.25MnO3 and Pr0.5Ca0.5Mn0.975Al0.025O3. A gigantic change in dielectric permittivity was detected near the percolation threshold. The hysteresis in dielectric permittivity as well as in resistivity supports the first order nature of the insulator-metal transition while the tunability is due to the coexisting of phases across the transition. A highly resistivity correlated dielectric behaviour has been observed throughout the insulator to metal transition evidencing the dielectric catastrophe phenomenon. The field dependent dielectric data are analyzed in the framework of Maxwell-Garnett theory in association with Mott-Hubbard model.