Showing papers on "Dielectric published in 1986"

Handbook of glass properties

Abstract: Introduction. Commercial Glasses: Vitreous Silica. Commerical Glasses. Thermodynamic and Thermal Properties: Density. Surface Tension. Coefficient of Thermal Expansion. Heat Capacity. Thermal Conductivity. Mechanical Properties: Viscosity. Elastic Properties. Microhardness. Strength. Electrical and Transport Properties: Electrical Conductivity. Dielectric Properties. Ionic Diffusion. Other Properties: Refractive Index and Dispersion. Solubility, Permeability, and Diffusion of Gases in Glass. Chemical Durability. Estimation of Properties. Appendices. Systems Index. Subject Index.

Focusing of electric fields in the active site of Cu‐Zn superoxide dismutase: Effects of ionic strength and amino‐acid modification

Abstract: In this paper we report the implementation of a finite-difference algorithm which solves the linearized Poisson-Boltzmann equation for molecules of arbitrary shape and charge distribution and which includes the screening effects of electrolytes. The microcoding of the algorithm on an ST-100 array processor allows us to obtain electrostatic potential maps in and around a protein, including the effects of ionic strength, in about 30 minutes. We have applied the algorithm to a dimer of the protein Cu-Zn superoxide dismutase (SOD) and compared our results to those obtained from uniform dielectric models based on coulombic potentials. We find that both the shape of the protein-solvent boundary and the ionic strength of the solvent have a profound effect on the potentials in the solvent. For the case of SOD, the cluster of positive charge at the bottom of the active site channel produces a strongly enhanced positive potential due to the focusing of field lines in the channel—a result that cannot be obtained with any uniform dielectric model. The remainder of the protein is surrounded by a weak negative potential. The electrostatic potential of the enzyme seems designed to provide a large cross-sectional area for productive collisions. Based on the ionic strength dependence of the size of the positive potential region emanating from the active site and the repulsive negative potential barrier surrounding the protein, we are able to suggest an explanation for the ionic strength dependence of the activity of the native and chemically modified forms of the enzyme.

Rigorous coupled-wave analysis of metallic surface-relief gratings

Abstract: A rigorous coupled-wave analysis for metallic surface-relief gratings is presented. This approach allows an arbitrary complex permittivity to be used for the material and thus avoids the infinite conductivity (perfect-conductor) approximation. Both TE and TM polarizations and arbitrary angles of incidence are treated. Diffraction characteristics for rectangular-groove gold gratings with equal groove and ridge widths are presented for free-space wavelengths of 0.5, 1.0 and 10.0 μm for all diffracted orders as a function of period, groove depth, polarization, and angle of incidence. Results include the following: (1) TM-polarization diffraction characteristics vary more rapidly than do those for TE polarization, (2) 95% first-order diffraction efficiency occurs for TM polarization at 10.0 μm, (3) 50% absorption of incident power occurs at 0.5 μm, and (5) the perfect-conductor approximation is not valid for TM polarization at any of the wavelengths and is not valid for TE polarization at 0.5 μm.

The dielectric constant of a folded protein.

Abstract: The goal of this paper is to obtain a theoretical estimate of the dielectric constant of a folded protein. To this end, we develop a form of the Kirkwood–Frohlich dielectric theory that applies to polar solids and folded proteins. The resulting theory incorporates a factor expressing the degree to which dipolar groups are constrained within the material's structure, as well as a generalized form of Kirkwood's correlation factor. The theory is applied to a hypothetical isotropic protein composed of randomly oriented α-helices and having a number density of dipolar groups equal to that found in actual proteins. The factor of constraint and the generalized dipole correlation factor are calculated using normal mode analysis. Temperature factors are also computed by normal mode analysis and are in reasonable agreement with those found experimentally. The computed dielectric constant is low; the best estimate is that it falls between 2.5 and 4.

Preparation of c‐axis oriented PbTiO3 thin films and their crystallographic, dielectric, and pyroelectric properties

Abstract: Highly c‐axis oriented and epitaxial PbTiO3 thin films were grown on MgO single crystals and epitaxial Pt film substrates by the rf‐magnetron sputtering method. The films with a 98% c‐axis orientation rate were obtained under low deposition rate (<20 A/min) and low gas pressure (∼1 Pa) using a PbO‐rich target. Phase transition of the PbTiO3 thin film was studied by high‐temperature x‐ray diffraction. It was found that the c‐axis of the tetragonal phase was parallel to the substrate just below Tc and the c‐axis becomes perpendicular to the substrate with lowering of temperature. These films show high resistivity (∼1010/Ω cm). It was found that significant pyroelectric currents are detected on all specimens without poling treatment. The polarization directions of the films are the same in all specimens. One of these films had a low relative dielectric constant of 97 and a high pyroelectric coefficient of 2.5×10−8 C/cm2 K without poling treatment. These films will be suitable for applications such as pyroelectric infrared detector and piezoelectric transducer.

Ab initio calculation of the macroscopic dielectric constant in silicon.

Abstract: We perform a first-principles calculation of the static dielectric constant of Si in the framework of density-functional theory. The only essential approximation used in this work is the local-density approximation (LDA): norm-conserving pseudopotentials and large plane-wave basis sets are used, numerical roundoff and convergence errors are kept below 1%. The present calculation gives for the first time the ``exact'' value of the macroscopic dielectric constant at the LDA level. The theoretical value of ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ is 12% higher than experiment.

Dielectric relaxation in water. Computer simulations with the TIP4P potential

Abstract: In this second paper in a series of systematic investigations seeking to relate the dielectric properties of water to the features of the intermolecular potential, extensive molecular dynamics simulations with the empirical TIP4P effective pair potential are compared with the experimental data for water as well as with the results reported previously for the MCY a b i n i t i omodel. The frequency dependence of the dielectric constant obtained for the two models is contrasted with the predictions of a Mori three‐variable theory and analyzed in detail using a phenomenological description of dielectric relaxation. It is shown that both models are capable of reproducing all reorientational processes observed in the experimental spectrum. However, qualitative agreement with the experimental results for the Debye relaxation time and the static Kirkwood g‐factor g K is only obtained with the TIP4P model, although the values are still too low and ∂g K /∂T has the wrong sign. The differences between the models are interpreted as being due to the different position chosen for the center of negative charge, and it is argued that moving the latter further towards the oxygen would, for simple rigid point charge models, yield considerably improved agreement with experiment.

Self-regulating heater employing reactive components

Abstract: Novel electrical heater which are self-regulating as a result of appropriate combination of a constant current or constant voltage power source with a resistive heating component and a temperature-sensitive component. Preferred heaters comprise a plurality of heating units, each of which heating units comprises a reactive component, a resistive heating component, and a temperature-responsive component. Self-regulation of the heater may be achieved in a number of different ways, including the use of employing a reactive component and a temperature-responsive component which form a combination exhibiting an impedance which changes with temperature. The temperature-responsive component can for example change in dielectric constant, or in permeability or in shape, or can effect changes in the frequencies inputted to the reactive component.

Ion-based methods for optical thin film deposition

Abstract: The optical properties of the dielectric oxide films SiO2, Al2O3, TiO2, ZrO2, CeO2 and Ta2O5 produced by ion-based techniques have been reviewed. The influence of ion bombardment during deposition is discussed in some detail and the various production techniques are described. Recent results on the deposition and properties of diamond-like carbon films are also reviewed. Finally, some examples of the practical applications of high quality dielectric oxide films are given.

Electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects

Abstract: The recent development and extension of the method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations. The surfaces of the homogeneous three-dimensional arbitrary geometrical shapes are modeled using surface triangular patches, similar to the case of arbitrary shaped conducting objects. Further, the development and extensions required to treat efficiently three-dimensional lossy dielectric objects are reported. Numerical results and their comparisons are also presented for two canonical dielectric scatterers-a sphere and a finite circular cylinder.

Some considerations on the electric field induced in insulators by electron bombardment

Abstract: Starting from a simple model of the distributions of charge created in an insulator by bombardment with electrons, the components of the electric field are evaluated by using Maxwell’s equations and image effects. The results are applied to the most common experimental situations: a semi‐infinite sample (i) bounded by a vacuum or (ii) covered by a conducting film, and a sample in the form of a film (iii) unsupported or (iv) covering a conducting substrate. The results are compared to some experimental data concerning, for instance, electromigration and electron‐stimulated desorption. In surface analysis the decay of the Auger signal from ions of opposite charges and the opposite behavior of ions of the same charge are explained. Similar effects observed in electron‐probe microanalysis of glasses are also elucidated. The results concern scanning electron microscopy, transmission electron microscopy, and electron‐beam lithography applied to biological objects, polymers, ceramics, minerals, glasses, and electronic devices. With slight modifications, the same model can be applied to cases of irradiation with ions or x rays. The evolution of the trapped charges with time is suggested, and the need to indicate the electric parameters (e and γ) of the investigated samples is outlined.

Electro-optic and dielectric properties of KTiOPO4

Abstract: The electro‐optic and dielectric properties of potassium titanyl phosphate (KTP) have been measured from dc to 1 GHz and are compared with other electro‐optic materials. KTP is shown to possess a combination of properties that make it unique for a variety of electro‐optic modulator applications.

Optical constants and associated functions of metastable diamondlike amorphous carbon films in the energy range 0.5–7.3 eV

Abstract: The complex refractive index N(ω)=n+ik and the complex dielectric constant e(ω)=e1+ie2 are presented for diamondlike amorphous carbon (a‐C) films in the photon energy range 0.5–7.3 eV. The effective number of valence electrons neff per carbon atom, the static dielectric constant e0,eff, and the energy loss function Im[−1/e(ω)] are deduced via the use of sum rules and are used to interpret the optical data. The a‐C films were deposited using an unbalanced magnetron gun to sputter a graphite target (effective sputtering area of 20 cm2) in ultrapure argon gas. The magnetron is characterized by a high deposition flux of condensing atoms (1.5×1014–1.2×1016 cm−2 s−1) and a concomitant high ion flux (6×1014–2.5×1016 cm−2 s−1). A series of films were prepared by sputtering at different power levels in the range 5–500 W. Insulating substrates were used which allowed the films to self‐bias negatively with respect to the plasma, so that the films were bombarded during their growth by Ar+ ions of energy 16–13 eV at a...

A fractal model of dielectric breakdown and prebreakdown in solid dielectrics

Abstract: We introduce and discuss a fractal model for dielectric breakdown which exhibits a breakdown voltage and a region of stable prebreakdown structures. The model provides a unifying picture covering homogeneous space charge injection, treelike structures, and filamentary breakdown. A simple qualitative relation between the global form of the pattern and two simple physical parameters is found. The model illustrates the intricate relationship between local stochastic and global deterministic aspects of dielectric instablilities.

Theoretical Study of the Anomalies of Coated Dielectric Gratings

Abstract: The zero-order diffraction efficiency anomalies of a corrugated dielectric waveguide are studied theoretically in detail. A new and surprising phenomenon is observed: the efficiency changes from 0 to 100 per cent in the vicinity of the excitation of guided waves. The fundamental parameters of the system are found in the case where only one order is propagating and some of their properties are shown. The behaviour of the efficiency curves is explained by a phenomenological theory and a comparison with numerical rigorous results is made.

Dielectric Analysis of Thermoset Cure.

Abstract: All dielectric measurements involve the determination of the electrical polarization and conduction properties of a sample subjected to a time-varying electric field. Section 2 addresses dielectric measurement methods, the various instruments and electrodes, and their calibrations. Section 3 examines the microscopic mechanisms giving rise in the observed microscopic dielectric properties, and Section 4 explores in detail the effects of temperature and cure on these properties. Finally, Section 5 contains a selected bibliography of applications of dielectric analysis to the study of thermoset cure.

Dielectric-fibre surface waveguides for optical frequencies

Abstract: A dielectric fibre with a refractive index higher than its surrounding region is a form of dielectric waveguide which represents a possible medium for the guided transmission of energy at optical frequencies. The particular type of dielectric-fibre waveguide discussed is one with a circular cross-section. The choice of the mode of propagation for a fibre waveguide used for communication purposes is governed by consideration of loss characteristics and information capacity. Dielectric loss, bending loss and radiation loss are discussed, and mode stability, dispersion and power handling are examined with respect to information capacity. Physicalrealisation aspects are also discussed. Experimental investigations at both optical and microwave wavelengths are included.

Epitaxial growth and the crystallographic, dielectric, and pyroelectric properties of lanthanum-modified lead titanate thin films

Abstract: Using an rf‐magnetron sputtering method, highly c‐axis‐oriented La‐modified PbTiO3 (PLT) thin films with compositions of Pb1−xLaxTi1−x/4O3, where x=0.05, 0.10, and 0.15, have been obtained on MgO single‐crystal and epitaxial Pt thin‐film substrates under conditions of low gas pressure and low deposition rate. The degree of c‐axis orientation of the PLT films decreases, and the tetragonality of PLT becomes smaller with increasing La content. The Curie point of the films decreases at a rate of 18 °C/at. % of La with an increase of La content. D‐E hysteresis loops were observed, and these became slim and symmetric with increasing La. It was found that significant pyroelectric currents are detected on all as‐grown specimens even without a poling treatment, and the directions are the same in all specimens. Relative dielectric constant er decreases, and pyroelectric coefficient γ increases with increasing degree of c‐axis orientation. er and γ became large with increase of La content in the films. Considering the figure of merit for pyroelectric infrared detection and the temperature coefficient of γ, it was concluded that PLT films with x=0.10 were good material for pyroelectric infrared detectors.

A dielectric hybrid mode antenna feed: A simple alternative to the corrugated horn

Abstract: A hybrid-mode horn antenna has been analyzed theoretically and experimentally. It consists of a conical metal horn with a dielectric core inside, separated from the metal wall by another dielectric layer with lower permittivity than for the core material. It is characterized by a very simple design and excellent electrical performance. The horn can support the balanced hybrid HE 11 -mode, and exhibits low cross polarization and low sidelobes over a wide frequency range. Compared to corrugated horns, the new horn has a simpler design, is easier to analyze, and has the potential of similar cross-polar bandwidth as for corrugated horns with ring-loaded corrugations. Drawbacks are the effects of dielectric losses. Thus the new horn represents an attractive alternative to the corrugated horn antenna.

Low-Temperature Phase Relationships in the System ZrO2-TiO2

Abstract: ZIRCONIUM TITANATE solid solutions are of interest for their useful dielectric properties in the microwave frequency regime. The authors have shown that solid-solution formation with SnO/sub 2/, as in commercial dielectric compositions, is effective in stabilizing the high-temperature structure of these materials. This high-temperature structure is of the type known as ..cap alpha..-PbO/sub 2/, space group Pcnb, number 60. The space group implies a random cation distribution on the available sites and has been confirmed using Reitveld total profile analysis of neutron powder diffraction data obtained using specimens prepared during this work. Single-phase, ..cap alpha..-PbO/sub 2/-type zirconium titanate solid solutions with compositions Zr/sub 1+x/Ti/sub 1-x/O/sub 4/ (1/10 > x > - 1/6) can be prepared by solid-state reaction. The phase transition, as observed during cooling is characterized by a gradual contraction of the unit-cell volume in the temperature range 1400/sup 0/ to 1050/sup 0/C. A major inflection, especially apparent in the c-axis length, is observed between 1200/sup 0/ and 1100/sup 0/C.

A Broad-Band, Automated, Stripline Technique for the Simultaneous Measurement of Complex Permittivity and Permeability

Abstract: A broad-band automated technique for making frequency-swept measurements of complex permittivity and permeability simultaneously is described. Epsilon/sub r/ and µ/sub r/ are computed from S-parameter measurements made on a strip transmission-line device loaded with the material under test. The derivation of epsilon/sub r/ and µ/sub r/ as functions of S/sub 11/ and S/sub 21/ is included, as well as a practical design for a stripline sample holder. Measured epsilon/sub r/ and µ/sub r/ data for several dielectrics and ceramic ferrites is also presented. The technique has been found to have an overall accuracy of better than +-5 percent.

Dielectric relaxation in poly(ethylene terephthalate)

Abstract: Mesure de la constante dielectrique et de la perte dielectrique entre 1 et 100 kHz. Mesure du volume massique en fonction de la temperature

Finite-Difference Analysis of Rectangular Dielectric Waveguide Structures

Abstract: A class of dielectric waveguide structures using a rectangular dielectric strip in conjunction with one or more layered dielectrics is analyzed with a finite-difference method formulated directly in terms of the wave equation for the transverse components of the magnetic field. This leads to an eigenvalue problem where the nonphysical, spurious modes do not appear. Moreover, the analysis inclndes hybrid-mode conversion effects, such as complex waves, at frequencies where the modes are not yet completely bound to the core of the highest dielectric constant, as well as at frequencies below cutoff. Dispersion characteristic examples are calculated for structures suitable for millimeter-wave and optical integrated circuits, such as dielectric image lines, shielded dielectric waveguides, insulated image guides, ridge guides, and inverted strip, channel, strip-slab, and indiffused inverted ridge guides. The numerical examples are verified by results available from other methods.

Magneto-optical recording medium

Abstract: A magneto optical recording medium comprising laminating a reflective layer, a dielectric undercoat layer and a hexagonal magnetoplumbite-type metal oxide magnetic layer on a substrate in order, characterized by that said magnetic layer is made an excellently C axis - orientated perpendicular magnetic film by putting the crystal misfit between said reflective layer and said dielectric undercoat layer formed thereon within ±30% and the crystal misfit between said dielectric undercoat layer and said hexagonal magnetoplumbite -type metal oxide magnetic layer formed thereon within ±30%, and thus various characteristics are widely improved.

Far Infrared Reflection Spectra of Ba(Zn,Ta)O3‐BaZrO3 Dielectric Resonator Material

Abstract: The dielectric ceramic materiala Ba(Zn1/3Ta2/3)O3–BaZrO3 has extremely low dielectric loss at microwave frequencies. To investigate the lattice vibrations of Ba(Zn,Ta)O3 and Ba(Zr, Zn, Ta)O3 solid solutions, far infrared reflection spectra were measured from 50 to 4000 cm−1 using a Fourier transform infrared spectrometer. These data were analyzed according to the classical dispersion theory. The spectra of Ba(Zn,Ta)O3 are well fitted by using the 14 resonant modes, and the spectra of Ba(Zr, Zn, Ta)O3 solid solution are fitted by assuming the normal distribution on resonant frequencies. The damping constant of these materials is discussed, and the values of tan δ calculated from the dispersion parameters agree with the measured values.

Applicability of Effective-Medium Theories to problems of Scattering and Absorption by Nonhomogeneous Atmospheric Particles

Abstract: Effective-medium theories yield effective dielectric functions (or, equivalently, refractive indices) of composite media. Such theories have been formulated that go beyond the Maxwell-Garnett and Bruggeman theories, which art restricted to media composed of grains much smaller than the wavelength. These extended effective-medium theories do not, however, yield effective dielectric functions that can be used for the same purposes for which we unhesitatingly use the dielectric functions of substances such as pure water and pure ice (e.g., reflection and transmission by smooth interfaces; absorption and scattering by particles). Extended dielectric functions can lead to unphysical results; for example, absorption in composite media with nonabsorbing components. Moreover, if the grains in composite media are large enough to give rise to magnetic dipole and higher-order multipole radiation, then the effective permeability of the composite medium cannot be taken to be that of free space even if the gra...

Comparison of electrical mixture rules for composites

Abstract: Firstly the basic theoretical methods of calculating the dielectric properties of heterogeneous mixtures are discussed. These are the mean field and effective medium theories and integral methods. Formulae are presented for systems containing parallel oriented ellipsoids and for randomly oriented ellipsoidal systems. Theoretical formulae are divided into two sub-groups: symmetric equations for statistical mixtures and asymmetric equations for matrix-inclusion type composites. In the former case only the relative amount of the components is important, in the second case phase inversion results in a change of the dielectric properties. Formulae are compared numerically using spherical and spheroidal systems with sharply different components (permittivity ratio is 1 ∶ 100). In the case of asymmetric formulae the effect of phase inversion is studied as well. Percolation behaviour predicted by the equations is demonstrated and discussed. Functional shapes are compared in relation to the theoretical differences. Finally, experimental data are compared with the theoretical results, advantages and drawbacks of the various formulae are discussed. For spherical systems the simplest mean field formula yields somewhat worse values than effective medium or integral equations. The Looyenga equation does not work very well if the permittivity difference is high. For nonspherical systems the fit is better in general, even the simplest formula works satisfactorily. The shape independence predicted by the Looyenga theory for randomly oriented ellipsoids is in conflict with experimental data.

Direct measurement of space‐charge injection from a needle electrode into dielectrics

Abstract: We show that space‐charge injection from a needle into a dielectric can be determined with a resolution of 10−15 °C, by using guarded needle electrodes and a charge compensating bridge circuit. The technique is applied to epoxy resin samples. A well‐defined homogeneous space‐charge cloud formation is observed in quantitative agreement with a field‐limiting space‐charge concept.