Showing papers on "Dielectric published in 1976"
TL;DR: In this article, the metal-non-metal transition takes place when the volume fraction of the metallic phase approaches the percolation threshold, and it is shown that the static dielectric constant diverges near the threshold.
Abstract: A system consisting of randomly distributed metallic and dielectric regions is considered. The metal-non-metal transition takes place when the volume fraction of the metallic phase approaches the percolation threshold. It is shown that the static dielectric constant diverges near the threshold. Critical indexes are introduced which describe the behaviour of the conductivity and the dielectric constant near the threshold as functions of the volume fraction and frequency. The case of non-zero dc conductivity of dielectric regions is considered also. It is shown that all indexes describing the critical behaviour of complex conductivity can be expressed by two indexes which are known from computer and model experiments. The results of computer calculations of Webman et al. are analysed.
719 citations
TL;DR: In this paper, the authors measured the dielectric constant κ in high-purity BaTiO3 ceramics as a function of temperature and showed that κ is quite dependent on grain size in the ferroelectric state.
Abstract: Measurements of the dielectric constant κ in high‐purity BaTiO3 ceramics as a function of temperature show that κ is quite dependent on grain size in the ferroelectric state while it is almost independent of grain size in the paraelectric state. In the ferroelectric orthorhombic and rhombohedral phases, κ decreases rapidly with lowering temperature when grain size is reduced smaller than 3 μm. It is also observed that the Curie temperature Tc is decreased very slightly, but the lower two transition points are shifted to higher temperatures as grain size decreases.
565 citations
TL;DR: In this article, the SCF equations for a system of electrons and nuclei surrounded by a dielectric continuum are derived by using a multipolar expansion of the interaction energy.
319 citations
TL;DR: In this article, the possibility of using Bragg reflection to obtain lossless confined propagation in slabs with a lower dielectric constant than that of the surrounding media is proposed and analyzed.
248 citations
TL;DR: In this paper, a two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed, and the parameters, a covalent and a polar energy, are fitted to the optical absorption spectra.
Abstract: A two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed. The parameters, a covalent and a polar energy, are fitted to the optical absorption spectra. The valence energy bands and density of states are calculated. In terms of these a consistent interpretation of all the observed photoemission and x-ray-emission spectra of ${\mathrm{SiO}}_{2}$ is obtained. The x-ray-absorption spectra are also analyzed. A bond-orbital approximation allows a simple calculation of the refractive index (or dielectric constant) of the various allotropic forms of silica and germania. Finally, the variation in total energy and charge distribution with local distortion is analyzed in order to study structural stability, elastic rigidity, and the effective charges (including dynamic contributions) which determine the piezoelectric constants and infrared absorption intensities.
244 citations
TL;DR: In this article, the complex dielectric, elastic and piezoelectric constants were measured for composites of epoxy resin and ferroelectric PZT ceramics at 10 Hz as a function of temperature, and the magnitudes and loss tangents of these constants were compared with the theoretical predictions.
Abstract: The complex dielectric, elastic and piezoelectric constants were measured for the composites of epoxy resin and ferroelectric PZT ceramics at 10 Hz as a function of temperature, and the magnitudes and loss tangents of these constants were compared with the theoretical predictions. The piezoelectric constants for a two phase system with piezoelectric spherical inclusions were expressed in terms of the properties of the constituents by use of the known expressions of the dielectric and elastic constants. The observed values of the d-constant (electric displacement/stress) were about 3/4 of the predicted. In the local mode dispersion region of epoxy resin near -30°C, the g-constant (electric field/stress) showed a larger temperature variation than the theoretical prediction.
224 citations
TL;DR: All modes are found to be hybrid modes, although they very closely approximate linearly polarized TEM modes.
Abstract: The field configurations and propagation constants of the normal modes of a hollow rectangular dielectric waveguide have been determined. In addition, the coupling coefficients of a Gaussian free-space mode into the normal modes of a square guide were calculated. The attenuation of each mode is found to be inversely proportional to the cube of the guide aperture 2alpha and proportional to the square of the free-space wavelength lambda. For a hollow dielectric square guide with 2alpha = 1 mm and lambda = 10.6 microm, an attenuation of 0.140 dB/m is predicted for SiO(2) and 0.032 dB/m for BeO. All modes are found to be hybrid modes, although they very closely approximate linearly polarized TEM modes.
223 citations
TL;DR: In this article, Gandolfo et al. discuss the use of SAW filters for low-loss frequency multiplexers and frequency synthesizers in electronic warfare systems, and present a method to connect them.
Abstract: [ l ] D. A. Gandolfo, C. L. Grasse, and G. D. O’clock, Jr., “Surface acoustic wave components in electronic warfare systems,’’ Proc. of International Specialist Seminar on Component Performance and Systems Applications of Surface Acoustic Wave Devices, Sept. 1973, Aviemore Scotland, pp. 231-42. [ 2 ] K. R. Laker, A. J . Budreau, and P. H. Carr, “Interconnecting SAW filters for low loss frequency multiplexers and frequency synthesizers,” Proc. of I974 Ultrasonics Symposium, Nov. 1974, Milwaukee, Wisconsin, pp. 161-163.
204 citations
171 citations
TL;DR: In this paper, the dielectric constants of water + acetonitrile have been measured from 30815 to 27815 K over the entire composition range and deviations from ideality have been determined; they are mostly positive and show two maxima and one minimum Derived properties have been calculated: molar polarization, correlation factor of mixtures, and dipole moments of both components using the Mecke-Reuter treatment.
166 citations
TL;DR: In this article, the dielectric constants of GaAs, CdTe, and ZnSe and their temperature dependences were found from low-frequency capacitance measurements.
Abstract: The dielectric constants of GaAs, CdTe, and ZnSe and their temperature dependences were found from low‐frequency capacitance measurements. From 100 to 300 °K the dielectric constants vary linearly with temperature. No electric field dependence was found up to 104 V/cm, nor frequency dependence between 20 Hz and 1 MHz. The dielectric constants extrapolated linearly to 0 °K are 12.35±0.09, 10.31±0.08, and 8.80±0.07 for GaAs, CdTe, and ZnSe, respectively. The temperature coefficients λ (≡e (0)−1 de/dt) are 2.01×10−4/°K, 2.27×10−4/°K, and 1.71×10−4/°K, respectively, with an accuracy of ±0.02×10−4/°K.
TL;DR: In this article, the attenuation coefficient of cylindrical dielectric-rod waveguide was measured by a transmission method at 100 GHz and an 8 dB/m attenuation was obtained.
Abstract: Measurements have been made of the attenuation coefficient of cylindrical dielectric-rod waveguide by a transmission method at 100 GHz. An 8 dB/m attenuation coefficient was obtained, caused half and half by the absorption due to losses in the dielectric and by the scattering due to irregularities and inhomogeneities in the dielectric.
TL;DR: In this paper, a study of the dielectric relaxation in polyethylenes rendered dielectrically active through oxidation (0.5-1.7 carbonyls/1000 CH2) and chlorination (14-22 Cl/1000 Ch2) was made and both linear and branched polymers were studied.
Abstract: A study was made of the dielectric relaxation in polyethylenes rendered dielectrically active through oxidation (0.5–1.7 carbonyls/1000 CH2) and chlorination (14–22 Cl/1000 CH2). Both linear and branched polymers were studied. All of the relaxations between the melt and −196° were studied in the frequency range 10 Hz to 10kHz (100 kHz in the chlorinated samples). In the linear samples a wide range of crystallinities was studied (55% in quenched specimens to 95% in extended-chain specimens obtained by crystallization at 5 kbar). As is consistent with its being a crystalline process, the α peak was found to discontinously disappear on melting of the samples and reappear on recrystallizing on cooling. The disappearance of the smaller crystals before the larger ones appeared to be evident in the isothermal loss versus frequency curves. The relaxation strength of the α process increases with crystallinity. The measured relaxation strength is less than that expected on the basis of direct proportionality to the crystalline fraction with full contribution of all dipoles in the crystalline material. However, the intensity is not sufficiently low for the process to be interpreted in terms of reorientation of localized conformational defects in the crystal. The variation of intensity with crystallinity is best interpreted in terms of full participation of crystalline dipoles but with selective partitioning of both carbonyls and chlorines favoring the amorphous domains. A strong correlation of the α loss peak location (Tmax at constant frequency or log fmax at constant T) with crystallinity for both carbonyl and chlorine containing polymers was found. This variation is interpreted in terms of chain rotations in the crystal where the activation free energy depends on crystal thickness. The dependence of log fmax and Tmax on lamellar thickness as well as a comparison with the loss peaks of ketones dissolved in parafins indicates that the chain rotation is not rigid and is accompanied by twisting as the rotation propagates through the crystal. In agreement with previous studies the β process is found to be strong only in the branched polymers but can be detected in the chlorinated linear polymer. The β process was resolved from the α in the branched samples by curve fitting and its activation parameters determined. The γ relaxation peak in oxidized polymers including its high asymmetry (low-temperature tail) and increasing emax with increasing frequency and temperature when plotted isochronally can be interpreted in terms of a simple nearly symmetrical relaxation time spectrum that narrows with increasing temperature. No increase in relaxation strength with temperature was found. The chlorinated polymers behave similarly but appear to have some Boltzmann enhancement (450–750 cal/mole) of relaxation strength with temperature. The dependence of relaxation strength on crystallinity indicates that the process is an amorphous one. Further, no evidence of relaxation peak shape changes with crystallinity that could be interpreted in terms of a crystalline component in addition to the amorphous one was found. The comparison of the γ relaxation strength with that expected on the basis of full participation of amorphous dipoles indicates that only a small fraction (∼10% in oxidized linear polymers) of them are involved in the relaxation. Thus it would seem that a glass–rubber transition interpretation is not indicated but rather a localized chain motion. It is suggested that the γ process, including its intensity, width, and activation parameters, can be interpreted in terms of an (unspecified) localized conformational (bond rotation) motion that is perturbed by differing local packing environments. The thermal expansion lessens the effects of variations in packing and leads to narrowing with increasing temperature. The conformational motion itself leads to increase in thermal expansion and hence a transition in the latter property. Some previously proposed localized amorphous phase conformational motions appear to be suitable candidates for the bond rotation motion. A weak relaxation peak found at temperatures below the γ and at 10 kHz may possibly be the dielectric analog of the δ cryogenic peak found previously mechanically at lower frequencies.
TL;DR: In this paper, a displaced Maxwellian approximation for the electron distribution function was used to calculate the hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond.
Abstract: Hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond has been calculated using displaced Maxwellian approximation for the electron distribution function. The effects of both the energy and momentum relaxation times due to scattering by acoustical, optical intervalley phonons and by ionized impurities are included in the derivations. Numerical results for the microwave conductivity and the change in dielectric constant as a function of frequency and bias electric field are presented. It is found that significant change in the conductivity and dielectric constant contribution for a fixed bias field occurs at very high frequencies on the order of 10 12 Hz, which is well beyond the range of current microwave device interest.
TL;DR: In this article, a new type of dielectric waveguide, which has a number of advantages over other previously available waveguide structures for millimeter-wave integrated circuits, is described.
Abstract: A new type of dielectric waveguide, which has a number of advantages over other previously available waveguide structures for millimeter-wave integrated circuits, is described. Dispersion characteristics and the field distributions in the waveguide are calculated using the concept of effective dielectric constant. Field distributions have been measured in the 80-GHz range in order to check the accuracy of the analytical results. This measurement has been done using a novel experimental technique, which should also be applicable to many other millimeter-wave waveguides and components.
TL;DR: Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz and the relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.
Abstract: Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz. The suspensions showed typical dielectric dispersions, which are considered to be caused by the presence of cytoplasmic membranes with sufficiently low conductivity. Since the conductivity of the cell wall was found to be of nearly the same value as that of the suspending medium, composed of KCl solutions in a range from 10 to 80mm, the cell wall may be ignored in establishing an electrical model of the cells suspended in such media. An analysis of the dielectric data was carried out by use of Pauly and Schwan's theory. The membrane capacitance was estimated to be 1.1±0.1 μF/cm2, which is compared with values reported so far for most biological membranes. The conductivity of the cell interior was almost unchanged with varying KCl concentrations and showed low values owing to the presence of less conducting particles, presumably intracellular organelles. The relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.
TL;DR: In this paper, the dielectric properties of hard red winter wheat were determined over a frequency range from 250 Hz to 12·1 GHz for moisture contents between 2·7% and 23·8% w.b.
01 Oct 1976
TL;DR: In this article, a new method is developed for accurately predicting resonant frequencies of dielectric resonators used in microwave circuits, by introducing an appropriate approximation in the field distribution outside the resonator, an analytical formulation becomes possible.
Abstract: A new method is developed for accurately predicting resonant frequencies of dielectric resonators used in microwave circuits. By introducing an appropriate approximation in the field distribution outside the resonator, an analytical formulation becomes possible. Two coupled eigenvalue equations thus derived are subsequently solved by a numerical method. The accuracy of the results computed by the present method is demonstrated by comparison with previously published data.
TL;DR: In this paper, it was shown that with increasing γ i of the dielectric panel material the firing voltage of an ac gas discharge display panel decreased, under the condition that the secondary electrons became greater than unity and unstable self-sustained emission was observed.
Abstract: From the measurement of the ion-induced secondary electron emission yield γ i it was shown that with increasing γ i of the dielectric panel material the firing voltage of an ac gas discharge display panel decreased. The measurement of the energy distributflon of the secondary electrons showed that the dielectric material with higher γ i has lower most-probable energy (MPE), and half-width (HW) values. The energy distribution introduced by Stolz in the ease of secondary electrons emitted from a metal was applied to the dielectric panel material and solved by using a computer. From this result, it was shown that the lower the electron affinity of the dielectric panel material, the higher is the γ i . Under the condition when γ i became greater than unity, unstable self-sustained emission was observed even though the primary ion beam was cut off.
TL;DR: In this paper, the theory of electron energy losses is discussed in terms of the electronic band structure of a solid and the relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed.
Abstract: The theory of characteristic electron energy losses is discussed in terms of the electronic band structure of a solid. The relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed. The transmission energy loss spectra of a number of the layer-type transition metal dichalcogenides, MX2, where M=Zr, Hf, Nb, Ta, Mo and W and X=S and Se, have been measured in the range of 0–50 eV. In the experiments, a beam of 50 keV electrons is incident along the c-axis of the crystals and electrons inelastically scattered through an angle of 1 m radian are selected for energy analysis. This ensures that the momentum transfer and hence the electric vector for the excitations lies in the basal plane of the crystal (E⊥c). Kramers-Kronig analysis has been applied to the energy loss data to deduce the complex dielectric function of each material. From this function, all other ‘optical’ constants, such as the reflectivity, and t...
TL;DR: In this article, permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions.
Abstract: The permittivity, refractive index, molecular dipole moment, dielectric relaxation parameters and molecular Kerr constant are reported for the nematogen 4,4-n-heptyl-cyanobiphenyl (HCB) in the nematic phase, in the pure isotropic phase and in benzene solutions. The anisotropy of molecular polarizability is less than in benzene. Kirkwood–Bordewijk g-factors show significant dipole antiparallelism in the isotropic and nematic phases: in the latter it is much larger parallel to the director axis than perpendicular to it. The two major (orthogonal) component activation enthalpy and entropy terms for dipole reorientation (Bauer) in the nematic phase (including benzene solutions) are compared with those in the isotropic media: in the pure nematic ΔHB(‖)= 60 ± 8 kJ mol–1; ΔHB(⊥)= 6 ± 2 kJ mol–1. The current theoretical representations of the nematic phase are examined using the experimental data. The occurrence of pre-transitional molecular interaction in benzene solutions (above 3 mol dm–3) and in the pure isotropic phase can be detected.
01 Apr 1976
TL;DR: In this paper, an open microwave resonator was used for dielectric measurements on unsintered polytetrafluoroethylene, high-density polyethylene and TPX.
Abstract: An investigation has been carried out into the use of an open microwave resonator for dielectric measurements. The resonator is of the hemispherical type and consists of one plane and one concave copper mirror. The sample is a plane parallel sheet of lateral dimensions ≥ 50 mm and is placed on the plane mirror. The theory has been extended to cover this type of resonator. Measurements on unsintered polytetrafluoroethylene, high-density polyethylene and TPX show that for materials with loss angles in the range 50–500 μrad the loss can be measured with standard deviation of ± 2% + 1μrad. The standard deviation for permittivity measurements is about ± 0.1%. A full discussion of the possible sources of error is given.
TL;DR: In this article, the effective electrical permittivity of polymer-coated steel was measured between 200 Hz and 100 kHz as a function of time of exposure to, and the real and imaginary parts of the permittivities increased over the entire frequency range as a consequence of electrolyte penetration.
Abstract: The effective electrical permittivity of polymer‐coated steel was measured between 200 Hz and 100 kHz as a function of time of exposure to . The real and imaginary parts of the permittivity increased over the entire frequency range as a consequence of electrolyte penetration. The development of a −1 slope on the log loss vs. log frequency curve suggested localized penetration of the dielectric coating by a conducting phase. This behavior correlated with the onset of visible localized corrosion. Results were discussed in terms of a metal/metal oxide/penetrated‐coating model.
TL;DR: In this article, the complementary use of dielectric and nuclear magnetic relaxation methods was developed to elucidate the molecular dynamics in aqueous solutions of small hydrophilic molecules, and hence determine extents of hydration.
Abstract: A strategy is developed for the complementary use of dielectric and nuclear magnetic relaxation methods to elucidate the molecular dynamics in aqueous solutions of small hydrophilic molecules, and hence determine extents of hydration. The nuclear magnetic relaxation data, as well as characterizing the motional properties of various carbohydrate solutes, is used here to test alternative models for the resolution of the dielectric spectra into their component relaxation processes. This approach results in a much more confident analysis of solvent relaxation properties than has in the past been usual, to yield information relating to the extents of hydration of small sugars and the possible orientation-specific nature of this hydration. It is demonstrated that the dielectric relaxation of the sugar molecules themselves is unequivocally not due to the reorientation of the whole molecule and most likely is dominated by the rotation of hydrate side chain groups (hydroxyls and hydroxymethyl). In proton magnetic relaxation studies of glucose in D2O it is observed that one particular proton (H-1 in the α-form only) is extremely susceptible to inter-molecular proton-proton interactions while the remaining protons are very effectively shielded. This observation is shown to be fully consistent with the conformational and hydration properties of glucose.
TL;DR: In this paper, the fringing field at the open end of the transmission line was perturbed by an unknown dielectric material, and the results showed that the method has sufficient accuracy for most applications up to about 4 GHz.
Abstract: The method is based on perturbing the fringing field at the open end of the transmission line by an unknown dielectric material, and is applicable not only for solid dielectric materials but also for liquids and gases. Forming or shaping of solid dielectrics is not required, but there should be a small area available for contact. Thickness of the dielectric material terminating the line does not affect the measurement unless the material is thinner than twice the spacing between conductors of the coaxial line. The experimental results obtained for some solid dielectric materials, liquids, and biological tissue shows that the method has sufficient accuracy for most applications up to about 4 GHz.
TL;DR: In this paper, a general formalism was used to obtain an expression for the dielectric constant of a diatomic polar fluid in terms of atom-atom correlation functions, which were then shown to be of comparatively short range, decaying line r−6 for large r for almost all densities and temperatures.
Abstract: A general formalism developed by us earlier is used to obtain an expression for the dielectric constant of a diatomic polar fluid in terms of atom–atom correlation functions. These functions are then shown to be of comparatively short range, decaying line r−6 for large r for almost all densities and temperatures.
TL;DR: In this paper, Monte Carlo results for the free energy and dielectric constant of systems of permanent dipoles disposed on the sites of simple cubic and face-centred cubic lattices as functions of the parameter ϑ = μ2ρ/kT are presented.
Abstract: Monte Carlo results are presented for the free energy and dielectric constant of systems of permanent dipoles disposed on the sites of simple cubic and face-centred cubic lattices as functions of the parameter ϑ = μ2ρ/kT. Alternative schemes are considered for taking account of the long-range character of the dipolar interaction, based on an Ewald-type sum or a reaction-field approximation; use of such a procedure is essential if the system is to have the correct dielectric properties. Different methods of calculating the dielectric constant are also compared. It is shown that the two methods of treating the long-range contribution to the energy lead to similar results for the dielectric constant, but use of the Ewald method apparently introduces a small but systematic error. The results on both free energy and dielectric constant are discussed in the light of predictions of a number of analytical approaches. In the case of the simple cubic lattice the general trend in the computed dielectric constant as ...
TL;DR: The mathematical expressions for skin impedance have been determined and both relaxations due to the cellular inhomogeneous structure and the morphological laminate structure are estimated from the complex dielectric constant and integral operation, respectively.
Abstract: It is important for an understanding of skin impedance that the formative mechanism of the stratum-corneum impedance is analysed. The structural features of the stratum corneum are found in the inhomogeneous and the laminate structure of dead cells. (i) The mathematical expressions for skin impedance have been determined. Both relaxations due to the cellular inhomogeneous structure and the morphological laminate structure are estimated from the complex dielectric constant and integral operation, respectively. (ii) The dielectric constant of the stratum corneum decreases at first and then increases exponentially towards the deeper tissues. Conversely, the resistivity decreases in an exponential fashion. These values depend only on the relaxation due to the inhomogeneous structure. (iii) The model of the skin impedance in which the dielectric component is homogeneous and only the resistive component has the laminate structure, can hardly explain the frequency dispersions of the dielectric constant and the resistivity.
Journal Article•
TL;DR: The dielectric behavior of a solution consisting of the macrodipole is one major concern of the study, and the other is to probe with this unique property into the regular conformation and helix-coil transition of polypeptides.
TL;DR: In this paper, phase transitions in triammonium hydrogen disulfate (NH4)3H(SO4)2 were studied by means of dielectric measurements and differential thermal analysis.
Abstract: Phase transitions in triammonium hydrogen disulfate (NH4)3H(SO4)2 were studied by means of dielectric measurements and differential thermal analysis. Below room temperature three phase transitions were observed at −8, −132, and −140°C. The dielectric constant along the c*-direction shows breaks at the −8 and −132°C transitions, while it shows a discontinuous change accompanied with a thermal hysteresis at the −140°C transition. In addition to the above-mentioned transitions, a broad maximum of the dielectric constant was found at about −28°C along the c*-direction. However, no thermal anomalies were observed around −28°C.
Mit Hilfe dielektrischer Messungen und differentieller Thermoanalyse wurden die Phasenubergange in Triammoniumhydrogendisulfat (NH4)3H(SO4)2 untersucht. Unterhalb der Raumtemperatur wurden drei Phasenubergange bei −8, −132 und −140°C gefunden. Die entlang der c*-Richtung gemessene Dielektrizitatskonstante zeigt bei den −8 und −132°C-Ubergangen stufenformige Anderungen, beim −140°C-Ubergang andert sie sich, begleitet von thermischen Hystereseerscheinungen, diskontinuierlich. Zusatzlich zu den o. g. Ubergangen wurden bei Messung in c*-Richtung ein breites Maximum der Dielektrizitatskonstanten bei etwa −28°C, aber keine thermischen Anomalien gefunden.