Showing papers on "Dielectric published in 1985"

GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications

Abstract: The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

Microwave Dielectric Behavior of Wet Soil-Part II: Dielectric Mixing Models

Abstract: This paper is the second in a series evaluating the microwave dielectric behavior of soil-water mixtures as a function of water content and soil textural composition. Part II draws upon the data presented in Part 1 [13] to develop appropriate empirical and theoretical dielectric mixing models for the 1.4-to 18-GHz region. A semiempirical mixing model based upon the index of refraction is presented, requiring only easily ascertained soil physical parameters such as volumetric moisture and soil textural composition as inputs. In addition, a theoretical model accounting explicitly for the presence of a hydration layer of bound water adjacent to hydrophilic soil particle surfaces is presented. A four-component dielectric mixing model treats the soil-water system as a host medium of dry soil solids containing randomly distributed and randomly oriented disc-shaped inclusions of bound water, bulk water, and air. The bulk water component is considered to be dependent upon frequency, temperature, and salinity. The soil solution is differentiated by means of a soil physical model into 1) a bound component and 2) a bulk soil solution. The performance of each model is evaluated as a function of soil moisture, soil texture, and frequency, using the dielectric measurements of five soils ranging from sandy loam to silty clay (as presented in Part I [13]) at frequencies between 1.4 and 18 GHz. The semiempirical mixing model yields an excellent fit to the measured data at frequencies above 4 GHz. At 1.

Dielectric properties of fine‐grained barium titanate ceramics

Abstract: Dielectric properties, lattice‐ and microstructure of ceramic BaTiO3 showing grain sizes of 0.3–100 μm were studied. At grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum er ≊5000 at grain sizes 0.8–1 μm. At grain sizes <0.7 μm the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.

Microwave Dielectric Behavior of Wet Soil-Part 1: Empirical Models and Experimental Observations

Abstract: This is the first paper in a two-part sequence that evaluates the microwave dielectric behavior of soil-water mixtures as a function of water content, temperature, and soil textural composition. Part I presents the results of dielectric constant measurements conducted for five different soil types at frequencies between 1.4 and 18 GHz. Soil texture is shown to have an effect on dielectric behavior over the entire frequency range and is most pronounced at frequencies below 5 GHz. In addition, the dielectric properties of frozen soils suggest that a fraction of the soil water component remains liquid even at temperatures of -24° C. The dielectric data as measured at room temperature are summarized at each frequency by polynomial expressions dependent upon both the volumetric moisture content m and the percentage of sand and clay contained in the soil; separate polynomial expressions are given for the real and imaginary parts of the dielectric constant. In Part II, two dielectric mixing models will be presented to account for the observed behavior: 1) a semiempirical refractive mixing model that accurately describes the data and requires only volumetric moisture and soil texture as inputs, and 2) a theoretical four-component mixing model that explicitly accounts for the presence of bound water.

Microwave Measurement of Dielectric Properties of Low-Loss Materials by the Dielectric Rod Resonator Method

Abstract: Improvements both in accuracy and speed are described for the technique of measuring the microwave dielectric properties of low-loss materials by using a dielectric rod resonator short-circuited at both ends by two parallel conducting plates. A technique for measuring the effective surface resistance R/sub s/ of the conducting plates is proposed to allow the accurate measurement of the loss tangent tan delta. By means of the first-order approximation, the expressions are analytically derived for estimating the errors of the measured values of relative permittivity epsilon/sub r/, tan delta, and R/sub r/, for measuring the temperature coefficient of epsilon/sub r/, and for determining the required size of the conducting plates. Computer-aided measurements are realized by using these expressions. It is shown that the temperature dependence of R/sub s/, should be considered in the tan delta measurement. The copper plates used in this experiment have the relative conductivity of 91.0+-2.7 percent at 20°C, estimated from the measured R/sub s/ value. For a 99.9-percent alumina ceramic rod sample, the results measured at 7.69 GHz and 25°C show that epsilon/sub r/,= 9.687+-0.003 and tan delta = (1.6+-0.2)x 10/sup -5/. The temperature coefficients measured between 25 and 100°C are 112x10/sup -6//°C for epsilon/sub r/, and 23x10/sup -4//°C for tan delta.

The dielectric constant of water. Computer simulations with the MCY potential

Abstract: Despite the sizable literature on computer simulations of water and aqueous solutions, very little is known about one of the most interesting properties of water, namely its dielectric constant. In this paper it is demonstrated that the methodological as well as technological problems that have hitherto impeded the calculation of dielectric properties of realistic model systems have now been overcome. Using a small dedicated array processor, a series of extensive simulations with the MCY (Matsuoka–Clementi–Yoshimine) potential for water have been performed in reaction field geometry, and it is shown that consistent (i.e., free from boundary effects) and accurate results may be obtained for the full frequency‐dependent dielectric constant, from the static up to the submillimeter range. At the same time it is found that the rather popular MCY model is not able to satisfactorily reproduce the dielectric properties of real water: Both the static dielectric constant and the principal dielectric relaxation time are much lower than the experimental values, and the temperature dependence of the Kirkwood g factor has the wrong sign. It is concluded that in the future the calculation of the dielectric constant, being a measure of orientational correlations between molecules, will play an important part in assessing the reliability of model potentials for water.

Electrostatic effects in proteins

Abstract: 1 PERSPECTIVE AND OVERViEW 387 2 PROTEIN STRUCTURES AND ELECTROSTATIC INTERACTION 389 2.1 Charge Site Geometry and Dielectric Value 389 2.2 Intrinsic Versus Effective and Observed pK Values 389 2.3 Solvent Accessibility and Effective pK Values 390 2.4 Peptide Dipole Partial Charges 394 3 COMPUTATION OF LONG-RANGE ELECTROSTATIC INTERACTIONS 395 3.1 Microscopic Electrostatic Calculations 395 3.2 Uniform and Nonuniform Dielectric Continuum Methods 397 3.3 Continuum Models with Dielectric Boundaries 399 4 SUMMARY 404 5 EXAMPLES OF PROTEIN ELECTROSTATIC FIELD CALCULATION 406 5.1 Effective pK Values 406 5.2 Protein Electrostatic Stabilization 408 5.3 Recognition and Binding 413

Full-Wave Analysis of Microstrip Open-End and Gap Discontinuities

Abstract: A solution is presented for the characteristics of microstrip open-end and gap discontinuities on an infinite dielectric substrate. The exact Green's function of the grounded dielectric slab is used in a moment method procedure, so surface waves as well as space-wave radiation are included. The electric currents on the line are expanded in terms of longitudinal subsectional piecewise sinusoidal modes near the discontinuity, with entire domain traveling-wave modes used to represent incident, reflected, and, for the gap, transmitted waves away from the discontinuity. Results are given for the end admittance of an open-ended line, and the end conductance is compared with measurements. Results are also given for the reflection coefficient magnitude and surface-wave power generation of an open-ended line on substrates with various dielectric constants. Loss to surface and space waves is calculated for a representative gap discontinuity.

Dielectric effects in biopolymers: The theory of ionic saturation revisited

Abstract: Electrostatic effects are believed to determine the molecular structure and function of macromolecules in many ways. In metallo-based enzymes and in metal-macromolecule interactions in solution, these effects may predominate. In order to tackle metal ion-nucleic acid interactions theoretically, a modification of Debye's distance-dependent dielectric function first proposed more than 50 years ago is proposed. This function more closely approximates physical reality at small interatomic separations. The theory proposed here yields a dielectric function that gives reasonable agreement with experimental data in preliminary calculations. 39 references, 4 figures, 6 tables.

Phase transitions and soft modes in sodium bismuth titanate

Abstract: The results of experimental studies of the crystal and domain structures of NaO, 5BiO, 5TiO3 as well as its lattice dynamics, dielectric, optical and other physical properties are considered. Nature of peculiar temperature points is discussed.

Simple hybrid mode horn feed loaded with a dielectric cone

Abstract: A conical horn loaded with a solid dielectric cone, separated from the metal wall by a thin layer of low-permittivity material or air, is analysed theoretically and tested experimentally. This simple feed exhibits excellent radiation properties, with a crosspolar bandwidth similar to that of a corrugated horn.

Dielectric waveguide using powdered material

Abstract: A flexible low-loss dielectric waveguide is made from a flexible low-dielectric constant hollow cylinder filled with high-dielectric constant powder Alternatively, a rigid or semi-rigid waveguide comprises a groove formed in a low-dielectric constant substrate filled with high-dielectric constant powder

Millimeter wavelength dielectric waveguide having increased power output and a method of making same

Abstract: A millimeter wavelength solid dielectric waveguide having either an undulng or roughened outer surface is disclosed. As configured, and properly designed, for the wavelength of interest, the non-cylindrical surface will not have any deleterious effects on the electromagnetic properties of the dielectric waveguide. Moreover, the novel surface treatment will greatly increase the amount of heat energy that can be dissipated by radiation and convection from the dielectric waveguide thereby increasing its power handling capability.

Infrared Intensities of Liquids I: Determination of Infrared Optical and Dielectric Constants by FT-IR Using the CIRCLE ATR Cell:

Abstract: The CIRCLE ATR accessory has been used to measure the optical and dielectric constants of organic liquids and water. The method, based on Fresnel's equations, is described in detail, and the agreement between the results obtained and literature values is shown to be adequate for chemical use. The utility of optical and dielectric constants for the calculation of traditional infrared intensities in liquids and of dipole moment derivatives is outlined.

Preparation and basic properties of PbTiO3 ferroelectric thin films and their device applications

Abstract: A series of technical data for preparing PbTiO3 ferroelectric thin films and their applications to some electronic devices have been presented. PbTiO3 thin films having considerably good ferroelectric properties have been obtained by rf sputtering or CVD. Maximum dielectric constant and remanent polarization are about 200 and 27μC/cm2, respectively. Several attempts to fabricate electronic devices such as nonvolatile memory, infrared sensor, ultrasonic sensor and low-threshold electroluminescent devices have been also carried out.

Scattering and absorption characteristics of lossy dielectric, chiral, nonspherical objects

Abstract: A procedure based on the T-matrix method is devised to study the electromagnetic response of chiral, (lossy) dielectric, nonspherical objects exposed to an arbitrary incident field. Reductions in the method for axisymmetric objects are discussed. Using the technique thus developed, the plane wave scattering and absorption characteristics of lossy dielectric, axisymmetric scatterers (spheres as well as prolate and oblate spheroids), with and without chiral properties, are examined at frequencies above 50 GHz. The relative permittivity of the objects is assumed to be frequency dependent, whereas the chiral parameters are set to be constant in the numerical study. From the computed results, it appears that chiral spheres are the most effective objects in retarding the progress of an incident plane wave regardless of its polarization.

Coherent time-domain far-infrared spectroscopy

Abstract: A new approach to far-infrared spectroscopy is described that uses extremely short far-infrared pulses to measure the dielectric properties of materials. Optical rectification of femtosecond optical pulses is used to produce a Cerenkov cone of pulsed far-infrared radiation of approximately one cycle in duration in the terahertz spectral range. The coherent detection of the electric field of these far-infrared pulses by electro-optic sampling provides a capability for measuring precise changes in the shape of the waveform following reflection or transmission from materials. This method, which is equivalent to having a tunable laser in the spectral range from 0.1 to 2 THz, is illustrated by the measurement of the dielectric response of a solid-state plasma in n-type germanium and a GaAs/GaAlAs multi-quantum-well superlattice.

A polyimide-based capacitive humidity sensor

Abstract: The design of a relative humidity sensor is studied in which the principle of operation is based on the change of dielectric constant of a thin film of polyimide. The design of the sensor is established in such a way that it would be suitable for an integrated-circuit type of fabrication. The studies have shown that the experimental data are described well by the use of the Looyenga equation for dielectric constant behavior coupled with the Dubinin equation to describe the absorption as a function of relative humidity.

Geometrical model of conductive and dielectric properties of partially saturated rocks

Abstract: Dielectric constant and conductivity of three‐component porous media are calculated using a geometrical model Applications are made to experiments on clay‐free sedimentary rocks partially saturated with hydrocarbon and water, and air and water A good agreement with experimental data at high frequency (GHz) is obtained using only a spherical grain shape The low‐frequency (MHz) data cannot be explained by the spherical grain alone, but a bimodal distribution of spherical and platey grains gives a fair agreement The low‐frequency dielectric constant is very sensitive to the grain‐shape distribution, but at high frequency is not

Generation of surface excitations on dielectric spheres by an external electron beam

Abstract: The energy loss and differential probability of energy losses is calculated to all multipole orders for a charged particle moved uniformly past a sphere. The sphere's response is characterized by use of a local dielectric function.

Millimeter-wave dielectric measurement of materials

Abstract: It is no longer necessary to use extrapolated microwave dielectric values when designing millimeter-wave components and systems. Very recently, highly accurate millimeter-wave (5- to 1/2-mm) data on complex dielectric permittivity and loss tangent have become available to engineers for a variety of materials such as common ceramics, semiconductors, crystalline, and glass materials. One quasi-optical measurement method has proved to be most accurate and reproducible, namely, dispersive Fourier transform spectroscopy (DFTS) applied to a polarizing interferometer. The openresonator method and the Mach-Zehnder-IMPATT spectrometer will also be described and compared. The fact that the dielectric loss increases with frequency in the millimeter, unlike the microwave, is an important feature of these data. Reliable measurements also reveal that the methods of preparation of nominally identical specimens can change the dielectric losses by a factor of three.

The dielectric properties of brine in sea ice at microwave frequencies

Abstract: The dc conductivity and complex dielectric constant at frequencies of 7.50, 9, 11, 30, and 40 GHz of 16 samples of sea water brine in equilibrium with sea ice with freezing temperatures ranging from - 2.8\deg C to -25.0\deg C have been measured. The data is analyzed to yield parameters occurring in a Debye relaxation equation so that the dielectric constant of brine may be calculated throughout the microwave region of the electromagnetic spectrum.