Showing papers on "Dielectric published in 1977"
TL;DR: In this article, the dielectric constant of sea water has been measured at S-band and L-band with a quoted uncertainty of tenths of a percent, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower than X-band.
Abstract: The advent of precision microwave radiometry has placed a stringent requirement on the accuracy with which the dielectric constant of sea water must be known. To this end, measurements of the dielectric constant have been conducted at S -band and L -band with a quoted uncertainty of tenths of a percent. These and earlier results are critically examined, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower than X -band. At the higher microwave and millimeter wave frequencies, the accuracy is in question because of uncertainties in the relaxation time and the dielectric constant at infinite frequency.
834 citations
TL;DR: In this paper, the deformation potential of the phonons at the band edge has been determined for ZnO for photon energies between 1.6 and 3 eV, based on the first and second derivatives of the dielectric constant.
Abstract: The resonance of the Raman scattering by ${E}_{2}, {A}_{1T}, {E}_{1L}$, and ${E}_{1T}$ phonons, and several second-order features, has been studied for ZnO for photon energies between 1.6 and 3 eV. The results are interpreted with a dielectric theory based on the first and second derivatives of the dielectric constant. By combining our results with absolute scattering cross sections previously determined by Arguello et al. at 2.41 eV absolute values of the deformation potentials of the band edge can be determined. The difference in strength between the longitudinal and the transverse modes provides the signs of these deformation potentials. The antiresonance around 1.6 eV suggested by the earlier work of Callender et al. and attributed to a cancellation of the deformation potential and electro-optical contributions to the Raman tensor is confirmed. The deformation potentials of the ${A}_{1}$ phonons at the band edge have been obtained from a pseudopotential calculation. While the sign of these deformation potentials agrees with the experimental determination, their magnitudes do not agree. This fact is attributed to difficulties with the pseudopotential of the ${\mathrm{O}}^{2\ensuremath{-}}$ ion. An estimate of the deformation potentials from the dependence of the band edges on uniaxial stress is also made.
789 citations
TL;DR: In this paper, the dielectric constant of sea water has been measured at S-band and L-band with a quoted uncertainty of tenths of a percent, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower than X-band.
Abstract: The advent of precision microwave radiometry has placed a stringent requirement on the accuracy with which the dielectric constant of sea water must be known. To this end, measurements of the dielectric constant have been conducted at S -band and L -band with a quoted uncertainty of tenths of a percent. These and earlier results are critically examined, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower than X -band. At the higher microwave and millimeter wave frequencies, the accuracy is in question because of uncertainties in the relaxation time and the dielectric constant at infinite frequency.
718 citations
TL;DR: In this article, an internal bias field Ei which can exceed the coercive field strength was found to behave both like a field and thermally activated process in Pb(Ti, Zr)O3 ceramics doped with Al, Mn or Fe.
Abstract: Pb(Ti, Zr)O3 ceramics doped with Al, Mn or Fe exhibit constricted or asymmetrically displaced hysteresis loops. This distortion is due to an internal bias field Ei which can exceed the coercive field strength. Ei depends on the Ti/Zr ratio and on the kind of dope, and it increases with increasing doping concentration.After repeated cycling of the hysteresis loop the distortion disappears. This process, called “hysteresis relaxation,” obeys a time law of the form Ei(t) ∼exp(-t/τ)and is found to behave both like a field and thermally activated process. The activation energy of all investigated specimens doped with transition metal ions (Mn, Fe) lies between 0.6 and 0.7 eV, that of Al-doped samples is about 0.8 eV.Comparison of the behaviour of the dielectric and mechanical losses with that of the internal bias shows that these effects are closely correlated. From this correlation some conclusions can be drawn concerning the nature of Ei, the physical causes of the observed after-effects, and the influence o...
529 citations
TL;DR: In this paper, a relation between the normalized radiated powers radiated by magnetic and electric dipoles is established, and the authors show that the classical results for the radiated power yield the correct normalized spontaneous emission rates from an excited atomic state for electric and magnetic dipole transitions, respectively.
Abstract: Expressions for the total power radiated by magnetic and electric dipoles of arbitrary orientation located in a medium 1 at distance z0 from the interface to a homogeneous or planar stratified medium 2 are derived. A relation between the normalized powers radiated by magnetic and electric dipoles is established. For a homogeneous loss-free medium 2, curves of the normalized powers L(z0)/L∞ radiated by magnetic and electric dipoles versus the normalized distance z0/λ1 are presented for different values of the relative refractive index n = n2/n1 as the only parameter. The computer calculations are compared with analytical expressions derived for small and large distances. For n > 1, the contribution of the evanescent waves to the radiated power is calculated separately. We show that the classical results for the normalized radiated power yield the correct normalized spontaneous emission rates from an excited atomic state for electric and magnetic dipole transitions, respectively. We point out that the results for the electric dipole also give the change of the total power scattered by a small dielectric scattering particle when it is placed close to an interface.
469 citations
TL;DR: In this article, a self-consistent continuum model is developed from both local (stress tensor) and global (dissipation function) considerations, where the friction coefficient of a moving ion is computed in terms of the dimensionless coupling parameter.
Abstract: Presented herein is a thorough investigation of the consequences of coupling ion migration to dielectric relaxation in the solvent. A self‐consistent continuum model is developed from both local (stress tensor) and global (dissipation function) considerations. The friction coefficient of a moving ion is computed in terms of the dimensionless coupling parameter where e is the ion charge, η is the solvent viscosity, e0 and e∞ are the low and high frequency dielectric constants of the solvent, respectively, τD is the Debye dielectric relaxation time of the pure solvent, and R is the ionic radius. For small ions the computed frictional drag is practically independent of ion radius, provided some degree of hydrodynamic slip is allowed at the ion surface. The effect of ion migration on the dielectric relaxation time of the solution is analyzed in detail. It is shown that the Debye–Falkenhagen effect should lead to an increase in the observed relaxation time, while the kinetic ion–solvent coupling introduces one...
433 citations
01 Oct 1977
TL;DR: In this paper, the application of the dielectric method, especially the depolarization technique, for studying molecular mobilities, i.e., multiple phase transitions in polymeric systems, is discussed.
Abstract: The interest in studying electrical conduction and polarization phenomena in polymers has increased since last year. Besides the classical problems of conduction, polarization and breakdown in polymeric insulators, interesting for the electric and electronic industry, new aspects are being considered by more and more research groups in the field. One of these is the application of the dielectric method, especially the depolarization technique, for studying molecular mobilities, i.e., multiple phase transitions in polymeric systems. Combined with mechanical relaxation, thermal analysis, magnetic resonance and with some additional techniques dielectric spectroscopy is becoming a powerful tool for studying the phase-structure of such complex polymer systems as blends, filled, and reinforced materials. This way the dielectric technique is helpful in quality control even of such systems which are not used in the electrical or electronic industry.
421 citations
Patent•
29 Aug 1977TL;DR: In this paper, the authors describe a technique for uniform heating of relatively large blocks of hydrocarbonaceous formations in situ using radio frequency electrical energy that is substantially confined to the volume to be heated and effects dielectric heating of the formations.
Abstract: The disclosure describes a technique for uniform heating of relatively large blocks of hydrocarbonaceous formations in situ using radio frequency (RF) electrical energy that is substantially confined to the volume to be heated and effects dielectric heating of the formations. An important aspect of the disclosure relates to the fact that certain hydrocarbonaceous earth formations, for example raw unheated oil shale, exhibit dielectric absorption characteristics in the radio frequency range. In accordance with the system of the invention, a plurality of conductors are inserted in the formations and bound a particular volume of the formations. The phrase "bounding a particular volume" is intended to mean that the volume is enclosed on at least two sides thereof. Electrical excitation is provided for establishing alternating electric fields in the volume. The frequency of the excitation is selected as a function of the dimensions of the volume so as to establish a substantially non-radiating electric field which is substantially confined in the volume. In this manner, volumetric dielectric heating of the formations will occur to effect approximately uniform controlled heating of the volume.
396 citations
TL;DR: In this article, an experimental check of the Mie-Debye theory for the variation of radiation pressure on dielectric spheres with wavelength and size using optical-levitation techniques was performed.
Abstract: We report an experimental check of the Mie-Debye theory for the variation of radiation pressure on dielectric spheres with wavelength and size using optical-levitation techniques. Sharp resonances are observed which are shown to be related to dielectric surface waves. They permit particle-size measurement to a precision of 1 part in ${10}^{5}$ to ${10}^{6}$.
383 citations
TL;DR: In this paper, fine-grained monoclinic HfO 2 films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties.
351 citations
TL;DR: In this paper, a surface integral equation (SIE) technique is developed to analyze the scattering properties of arbitrarily-shaped lossy dielectric bodies of revolution, and the unknown surface currents (both electric and magnetic) are calculated by first, Fourier decomposition, and then, the moment method, Galerkin's procedure.
Abstract: A surface integral equation (SIE) technique is developed to analyze the scattering properties of arbitrarily-shaped lossy dielectric bodies of revolution. Two coupled vector integral equations formulated via Maxwell's equations, Green's theorem, and the boundary conditions are used. The unknown surface currents (both electric and magnetic) are calculated by, first, Fourier decomposition, and then, the moment method, Galerkin's procedure. The far scattered field and radar cross section (RCS) are then readily determined from the reciprocity theorem and the measurement matrix concept. For a dielectric sphere good agreement is obtained between the SIE and exact solutions. Solutions of a thick dielectric cylinder are next used to demonstrate the arbitrary geometry capability of the SIE method. This method is suitable for homogeneous dielectric bodies and only the axially incident plane wave is considered here. The method also applies for a wide range of dielectric parameters (with ∈r from 1.44 to 80 and conductivity σ from 0 to 103 mho/m).
TL;DR: In this paper, the temperature dependence of the phonon and electron contribution to the dielectric constant, e.g., in the c-and α-axes, was determined and compared to the capacitance measurements.
Abstract: Measurements of all A1 and E transverse and longitudinal phonons in BaTiO3 are reported in the temperature range 10 to 132 °C where the crystal is in the tetragonal phase. A least squares fitting of the spectral shapes is done and the resulting temperature dependence of the frequencies, linewidths and coupling parameters is presented. The temperature dependence of the phonon and electron contribution to the dielectric constant, e, in the c- and α-axes is determined and compared to the capacitance measurements. It is found that the dielectric constant discrepancy is highly anisotropic.
TL;DR: In this article, the angular distribution of the power radiated by magnetic or electric dipoles located at distance z 0 from a dielectric interface and oriented perpendicular to it is derived.
Abstract: We have derived analytical expressions for the angular distribution P(α) of the power radiated by magnetic or electric dipoles located at distance z0 from a dielectric interface and oriented perpendicular to it. For dipoles in the rarer medium very close to the interface, evanescent waves in the dipoles’ near field give rise to strong radiation into the denser medium. The resulting large maximum of P(α) shows characteristic differences for magnetic and electric dipoles when the relative refractive index of the two dielectrics is greater than √2. For dipoles lying on the interface a symmetry relation is established connecting the power distributions P(α) for the values n and 1/n of the relative refractive index.
TL;DR: In this paper, the general properties of snow are described with a view to engineering applications of data, including structural properties of deposited snow cover grain size, grain bonds, bulk density, overburden pressure, and permeability.
Abstract: The general properties of snow are described with a view to engineering applications of data. Following an introduction and a short note on the origins of snow, data are given for fall velocities of snow particles, and for mass flux and particle concentrations in falling snow and blowing snow. Notes on the structural properties of deposited snow cover grain size, grain bonds, bulk density, overburden pressure, and permeability. A section on impurities deals with stable and radioactive isotopes, chemical impurities, insoluble particles, living organisms, acidity, and gases. Mechanical properties are treated only selectively, and the reader is referred to another paper for comprehensive coverage. The selective treatment deals with stress waves and strain waves, compressibility, effects of volumetric strain on deviatoric strain, and specific energy for comminution. The section on thermal properties covers heat capacity, latent heat, conductivity, diffusivity, heat transfer by vapor diffusion, heat transfer and vapor transport with forced convection, and thermal strain. The section on electrical properties opens with a brief discussion on dielectric properties of ice, and proceeds to a summary of the dielectric properties of snow, including dielectric dispersion, permittivity, dielectric loss, and d.c. conductivity. There are also notes on the thermoelectric effect and on electrical charges in falling and blowing snow. The section on optical properties deals with transmission and attenuation of visible radiation, with spectral reflectance, and with long-wave emissivity. The review concludes with some comments on engineering problems that involve snow, and the requirements for research and development.
TL;DR: In this article, the dielectric-breakdown intensity threshold, critical power for self-focusing, and the power threshold for the production of spectral superbroadening have been measured in H2O and D2O.
Abstract: The dielectric-breakdown intensity threshold, the critical power for self-focusing, and the power threshold for the production of spectral superbroadening have been measured in H2O and D2O. For bandwidth-limited pulses of 30 psec duration at 1.06 microns and of 21 psec duration at 0.53 micron, the superbroadening in water always required power levels sufficient for catastrophic self-focusing and intensities equal to the electric breakdown threshold.
TL;DR: In this paper, the same Thomas-Fermi screening equation can be handled with different boundary conditions to describe screening in semiconductors, and the results for wave-number-dependent dielectric functions are obtained in simple analytical form.
Abstract: Thomas-Fermi (TF) screening in metals has been widely studied in the literature many years ago It is shown in this paper that the same TF equation can be handled with different boundary conditions to describe screening in semiconductors Explicit results for the wave-number-dependent dielectric function $\ensuremath{\epsilon}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ and for the spatial dielectric function $\ensuremath{\epsilon}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}})$ are obtained in simple analytical form A detailed comparison is done with the existing literature for diamond, Si, and Ge TF dielectric functions are found to be in excellent agreement with either Penn model and random-phase approximation dielectric functions
TL;DR: In this paper, the optical wave of wide-stripe lasers is found to be guided by changes in the real part of the dielectric constant that are caused by a dip in carrier concentration along the axis of the lasing filament.
Abstract: Experimental measurements of the optical-beam parameters of conventional oxide-insulated GaAs stripe-geometry lasers as a function of stripe width have shown a marked difference in the waveguide mechanism of narrow-stripe ( \simeq10 \mu m) and wide-stripe ( >20 \mu m) lasers. The optical wave of narrow-stripe lasers is guided by the previously reported gain-guiding mechanism. The optical wave of wide-stripe lasers is found to be guided by changes in the real part of the dielectric constant that are caused by a dip in carrier concentration along the axis of the lasing filament. This self-focused guiding has been predicted theoretically. These experimental results strongly support the hypothesis that in all cases the waveguides are formed predominantly by the naturally occurring variations in carrier concentration beneath the stripe. A new and fairly comprehensive mathematical model has been developed based on this assumption. The model predicts the carrier concentration, resultant gain, and dielectric constant profiles together with the optical-beam parameters and light/current characteristics of stripe-geometry lasers. The model is applicable over a wide range of stripe widths and device structures. The results are compared with experiment over the range of stripe widths from 10-20 \mu m and found in reasonable agreement. The effects of narrowing the stripe width below 10 μm are calculated and found to be in qualitative agreement with recently published experimental results. In particular the light-output power at which a predicted "kink" in the light/current characteristic occurs is found to increase rapidly as the stripe width reduces.
TL;DR: In this paper, the effects of texture on reflectivity and transmission through an exact calculation of a boundary layer whose complex dielectric constant is an appropriate average of the material and air was obtained.
Patent•
25 Jul 1977
TL;DR: In this article, a portable sensor is adapted to be moved along a wall to indicate a change in the dielectric constant of the wall thereby to signal the presence of a wall stud within the wall.
Abstract: A portable sensor adapted to be moved along a wall to indicate a change in the dielectric constant of the wall thereby to signal the presence of a wall stud within the wall. The sensor incorporates a capacitor plate positioned adjacent the surface in contact with the wall and a circuit for detecting any change in the capacitive charge on the capacitor. Any change in capacitive charge as the sensor is moved along the wall is due to a change in the dielectric constant of the wall because of the presence of a wall stud behind the wallboard. The sensor visually indicates any change in the dielectric constant in a manner to permit selection of the center of the change in dielectric constant thereby indicating the center of the wall stud. An additional feature of the circuit permits automatic calibration of the sensor to a level corresponding to the dielectric constant of the wallboard so that any change in the dielectric constant of the wall due to the presence of a stud is readily observable.
TL;DR: In this article, a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion was proposed to explain the dielectric anomalies of LiNbO3 and LiTaO3.
Abstract: Vitreous LiNbO3 and LiTaO3 have been prepared by roller quenching these compositions from the melt. The transparent glasses exhibit pronounced dielectric anomalies with peaks of e≳105 close to the crystallization temperature which are not characteristic of the crystalline phase. Pyroelectricity is induced after cooling the glass in an electric field. The data are discussed in terms of a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion.
TL;DR: In this paper, inverted-strip dielectric waveguides have been used as leaky-wave antennas and band-reject filters for millimeter-wave integrated circuits.
Abstract: Grating structures fabricated in inverted-strip dielectric waveguides have been used for the first time as leaky-wave antennas and band-reject filters. They are potentially useful for millimeter-wave integrated circuits. Experimental results agree reasonably well with theoretical predictions.
TL;DR: In this article, theoretical predictions and preliminary experimental results for a microwave source consisting of a dielectric loaded waveguide and an intense relativistic electron beam are compared and compared.
Abstract: Theoretical predictions and preliminary experimental results for a microwave source consisting of a dielectric loaded waveguide and an intense relativistic electron beam are compared.
TL;DR: The solar absorptance of a single ideal film on an idealized metallic substrate has been calculated as a function of its optical constants to determine the optimum parameters for selective absorber applications.
Abstract: The solar absorptance of a single ideal film on an idealized metallic substrate has been calculated as a function of its optical constants to determine the optimum parameters for selective absorber applications. High normal solar absorptances (>0.9) are possible for single uniform interference films if n < 1.5 and 0.2 < k < 0.8, values that are achievable using cermet materials. Grading the refractive index of single interference films improves the absorptance, with optimum results given by a uniformly increasing dielectric constant through the layer. With such a linear grading to air, normal solar absorptances of greater than 0.9 can be achieved for n < 1.5 and 0.1 < k < 5. Grading an absorbing material with a dielectric also improves the performance of the absorbing material. For bulk films, the optimum profile with minimum material is one where the dielectric constant increases slowly at the surface of the film.
TL;DR: In this paper, the effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied, and the average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy.
Abstract: The effects of Dy doping and sintering parameters on the properties of BaTiO3 ceramics were studied. The average grain size decreases with increasing Dy content and is controlled at ∼1.5 μ m by 0.8 at.% Dy. The Curie temperature change, associated with ≤1.2 at.% Dy, is <3°C. The dielectric constant is ∼2600 for specimens doped with 0.8 at.% Dy, calcined at 1200°C, and sintered at 1450°C. The dielectric constant variation with ambient temperature is much less than that of conventional BaTiO3 ceramics. Lattice constant c decreases with increasing Dy concentration whereas a increases slightly. The effects of grain size on dielectric constant, lattice parameters, and linear thermal expansion coefficient are more pronounced than the chemical effects of Dy doping in the ferroelectric state, whereas in the paraelectric state, these characteristics are almost independent of grain size as well as Dy concentration. The decrease in the frequency of occurrence of 90° twins with decreasing grain size implies that internal stress, which develops when BaTiO3 ceramics are cooled below Tc, strongly influences the effects of grain size.
TL;DR: In this paper, fine-grained nearly stoichiometric monoclinic ZrO2 films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties.
TL;DR: In this article, a model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated.
Abstract: A model of soil composed of a multiphase mixture of solid particles, water, and air voids is proposed from which the complex permittivity, or dielectric constant and conductivity, is calculated. It is based on the Hanai/Bruggelman/Wagner theory of mixtures and considers the ionic conducting water as partly dispersed and partly the dispersing medium, an important distinction with this theory. The permittivity as a function of frequency and water content is predicted. The increase in dielectric constant with water volume fraction does not differ greatly with soil type in the high-frequency limit and is approximated by a normal curve specified by the theory. A normal curve and the marked increase in dielectric constant at lower frequencies has been observed experimentally. It is concluded that this semidisperse theory of the dielectric permittivity is successful in describing the behavior of soils containing moisture in the high-frequency range (1 MHz-1 GHz). Approximations to the more detailed theory and a series-parallel RC equivalent circuit are given.
TL;DR: The qualitative differences between small self-trapped molecular polarons and dielectric polarons are stressed in this article, and the observable consequence of delay time before selftrapping is discussed, and applications are made to alkali halides and to SiO2.
Abstract: The authors discuss the self-trapping of a carrier or exciton in an insulator. The qualitative differences between small self-trapped molecular polarons and dielectric polarons are stressed. They point out that, for the formation of a molecular polaron or self-trapped exciton, a potential barrier must be penetrated or surmounted by the configuration coordinate, leading to a delay in the self-trapping process. This does not exist for dielectric polarons. The observable consequence of delay time before self-trapping is discussed, and applications are made to alkali halides and to SiO2.
TL;DR: In this article, the problem of scattering of electromagnetic waves of arbitrary frequency by a homogeneous, isotropic sphere which carries excess surface charges was solved under the assumption that there exists a linear relation between surface current density and electric field.
Abstract: The problem of scattering of electromagnetic waves of arbitrary frequency by a homogeneous, isotropic sphere which carries excess surface charges can be solved under the assumption that there exists a linear relation between surface current density and electric field The scattering coefficients so obtained are formally different from those in the standard Mie–Debye theory Whether or not there is any observable difference between scattering by a charged and otherwise identical uncharged sphere depends upon the value of a phenomenological surface conductivity or, equivalently, surface dielectric function For sufficiently small particles the effect of surface charges is merely additive, the effective dielectric function is the sum of bulk and surface dielectric functions
TL;DR: In this paper, the fluorescence lifetime of an excited molecule described as a classical oscillating dipole in front of a partially reflecting plane interface is studied theoretically, the lifetime being inversely proportional to the radiated power.