Showing papers on "Electric field published in 1983"

Field and wave electromagnetics

Abstract: 1. The Electromagnetic Model. Introduction. The Electromagnetic Model. Si Units and Universal Constants. Review Questions. 2. Vector Analysis. Introduction. Vector Addition and Subtraction. Products of Vectors. Orthogonal Coordinate Systems. Integrals Containing Vector Functions. Gradient of a Scalar Field. Divergence of a Vector Field. Divergence Theorem. Curl of a Vector Field. Stoke's Theorem. Two Null Identities. Helmholtz's Theorem. Review Questions. Problems. 3. Static Electric Fields. Introduction. Fundamental Postulates of Electrostatics in Free Space. Coulomb's Law. Gauss's Law and Applications. Electric Potential. Conductors in Static Electric Field. Dielectrics in Static Electric Field. Electric Flux Density and Dielectric Constant. Boundary Conditions for Electrostatic Fields. Capacitances and Capacitors. Electrostatic Energy and Forces. Solution of Electrostatic Boundary-Value Problems. Review Questions. Problems. 4. Solution of Electrostatic Problems. Introduction. Poisson's and Laplaces' Equations. Uniqueness of Electrostatic Functions. Method of Images. Boundary-Value Problems in Cartesian Coordinates. Boundary-Value Problems in Cylindrical Coordinates. Boundary-Value Problems in Spherical Coordinates. Review Questions. Problems. 5. Steady Electric Currents. Introduction. Current Density and Ohm's Law. Electromotive Force and Kirchoff's Voltage Law. Equation of Continuity and Kirchoff's Current Law. Power Dissipation and Joule's Law. Boundary Conditions for Current Density. Resistance Calculations. Review Questions. Problems. 6. Static Magnetic Fields. Introduction. Fundamental Postulates of Magnetostatics in Free Space. Vector Magnetic Potential. The Biot-Savart Law and Applications. The Magnetic Dipole. Magnetization and Equivalent Current Densities. Magnetic Field Intensity and Relative Permeability. Magnetic Circuits. Behavior of Magnetic Materials. Boundary Conditions for Magnetostatic Fields. Inductances and Inductors. Magnetic Energy. Magnetic Forces and Torques. Review Questions. Problems. 7. Time-Varying Fields and Maxwell's Equations. Introduction. Faraday's Law of Electromagnetic Induction. Maxwell's Equations. Potential Functions. Electromagnetic Boundary Conditions. Wave Equations and their Solutions. Time-Harmonic Fields. Review Questions. Problems. 8. Plane Electromagnetic Waves. Introduction. Plane Waves in Lossless Media. Plane Waves in Lossy Media. Group Velocity. Flow of Electromagentic Power and the Poynting Vector. Normal Incidence of Plane Waves at a Plane Conducting Boundary. Oblique Incidence of Plane Waves at a Plane Conducting Boundary. Normal Incidence of Plane Waves at a Plane Dielectric Boundary. Normal Incidence of Plane Waves at Multiple Dielectric Interfaces. Oblique Incidence of Plane Waves at a Plane Dielectric Boundary. Review Questions. Problems. 9. Theory and Application of Transmission Lines Introduction. Transverse Electromagnetic Wave Along a Parallel-Plate. Transmission Line General Transmission-Line Equations. Wave Characteristics on Finite Transmission Lines. Transients on Transmission Lines. The Smith Chart. Transmission-Line Impedance Matching. Review Questions. Problems. 10. Waveguides and Cavity Resonators. Introduction. General Wave Behaviors Along Uniform Guiding Structures. Parallel-Plate Waveguide. Rectangular Waveguides. Circular Waveguides. Dielectric Waveguides. Cavity Resonators. Review Questions. Problems. 11. Antennas and Radiating Systems. Introduction. Radiation Fields of Elemental Dipoles. Antenna Patterns and Antenna Parameters. Thin Linear Antennas. Antenna Arrays. Receiving Antennas. Transmit-Receive Systems. Some Other Antenna Types. Review Questions. Problems. Appendix A: Symbols and Units. Appendix B: Some Useful Material Constants. Bibliography. Answers to Selected Problems. Index. Back Endpapers.

Variational calculations on a quantum well in an electric field

Abstract: We present variational calculations of the eigenstates in an isolated-quantum-well structure subjected to an external electric field. At weak fields a quadratic Stark shift is found whose magnitude depends strongly on the finite well depth. In addition, the electric field induces a spatial shift of the particle wave function along or opposite to the field direction, depending on the sign of the particle mass. This field-induced spatial separation of conduction and valence electrons in GaAs quantum wells decreases the overlap between their associated wave functions, leading to a reduction of interband recombination.

Anisotropic orientation in molecular monolayers by infrared spectroscopy

Abstract: Fourier transform IR measurements of Langmuir–Blodgett monolayers have been made with both grazing incidence reflection and transmission techniques. The reflection arrangement at incident angles from 85° to 88° has the electric field component perpendicular to the substrate surface while the standard transmission arrangement has the electric field component in the plane of the film. These techniques were used to explore the anisotropic arrangement of cadmium arachidate molecules perpendicular and parallel to the monolayer plane. The implication of these results for characterizing the orientational anisotropy of chemical groups in thin polymer films is also discussed. In addition, the question of uniaxial and biaxial orientation in the monolayer plane was addressed because of the importance of intermolecular packing on both the extent and rate of polymerization in unsaturated fatty acid monolayer components which form synthetic membranes.

Comparison of S3-3 polar cap potential drops with the interplanetary magnetic field and models of magnetopause reconnection

Abstract: Measurements of the cross polar cap electric potential, by the double probe electric field experiment aboard S3-3, from 55 orbits in the dawn-dusk plane are compared with the reconnection electric fields predicted by a variety of models, both theoretical and experimental. The purpose of these comparisons is to understand the extent to which nonreconnection contributions to the polar cap potential must be included, to determine the time response of the polar cap potential to time varying reconnection rates, and to determine the efficiency and saturation levels of the reconnection process. It is found that (1) After several hours of northward interplanetary magnetic field, the cross polar cap potential declines to progressively lower values than those after 1 hour of northward interplanetary magnetic field. This suggests that it requires several hours for the ionospheric polar cap potential to respond to the ‘turning off’ or ‘turning down’ of the reconnection process. (2) The decay of the polar cap potential is used to demonstrate that contributions to the polar cap potential not associated with the reconnection process can be limited to less than 20 kV. It is shown that contributions to the polar cap potential that scale with the dynamic pressure of the solar wind are limited to less than 1 kV. (3) The cross polar cap electric potential is best predicted by a weighted sum of contributions from interplanetary magnetic field parameters over the 4 hours previous to the measurement. The weighting functions have the form of an exponential decay of 2–3 hours with the strongest weight on interplanetary parameters over the 1 hour previous to the measurement. (4) For values of the dawn dusk component of the interplanetary electric field less than about 0.5 mV/m, the measured polar cap potential is consistent with reconnection of all the interplanetary magnetic flux incident on a 30 RE wide frontside magnetopause. For larger values of the dawn dusk component of the interplanetary electric field, the proportion of field lines reconnecting is less, indicating saturation of the reconnection process. The above results are obtained when the extended response time of the magnetosphere to changes in interplanetary parameters is considered. They are independent of the detailed reconnection model assumed, and they are quite different from the viscous contribution, saturation levels of reconnection, and reconnection efficiencies inferred from comparisons of polar cap potentials to single hour averages of interplanetary parameters.

The Electromagnetic Field of an Insulated Antenna in a Conducting Or Dielectric Medium

Abstract: Insulated antennas are useful for localized heating as in the hyperthermia treatment of tumors and the extraction of shale oil. The distribution of current in and the admittance of a center-driven dipole embedded in a general medium are reviewed. Formulas for the electric field generated by the currents in the dipole are derived for all points outside the antenna. Near the antenna, the field is elliptically polarized. Formulas for the polarization ellipses are derived and evaluated for antennas with electrical half-lengths Beta/sub L/h = pi/4, pi/2, pi, and 3pi/2, where k/sub L/ =beta/sub L/ + i alpha/sub L/ is the wavenumber of the current, and this is different from the wavenumber of the ambient medium.

Two-dimensional magneto-quantum transport on GaAs-AlxGa1-xAs heterostructures under non-ohmic conditions

Abstract: Measurements of the conductivity sigma xx in the minima of the Shubnikov-de Haas oscillations on GaAs-AlxGa1-xAs heterostructures show that at helium temperatures a strong non-ohmic behaviour is observed with an instability in the current-voltage characteristic at electric field values of about 100 V cm-1 at B=7T. The data are analysed on the basis of an electric-field-dependent electron temperature.

Method and apparatus for offshore electromagnetic sounding utilizing wavelength effects to determine optimum source and detector positions

Abstract: An improved method and apparatus for electromagnetic surveying of a subterranean earth formation beneath a body of water. An electric dipole current source is towed from a survey vessel in a body of water substantially parallel to the surface of the body of water and separated from the floor of the body of water by a distance less than approximately one-quarter of the distance between the surface and the floor. Alternating electric current, preferably including a plurality of sinusoidal components, is caused to flow in the source. An array of electric dipole detectors is towed from the survey vessel substantially collinearly with the current source. Each electric dipole detector of the array is separated from the current source by a distance substantially equal to an integral number of wavelengths of electromagnetic radiation, of frequency equal to that of a sinusoidal component of the source current, propagating in the water. A gradient detector array is also towed by the survey vessel in a position laterally separated from, or beneath, the mid-point of the current source. Additionally, an array of three-axis magnetic field sensors mounted in controllable instrument pods are towed by the seismic vessel on the flanks of the current source. Frequency-domain and time-domain measurements of magnetic and electric field data are obtained and analyzed to permit detection of hydrocarbons or other mineral deposits, or regions altered by their presence, within subfloor geologic formations covered by the body of water.

Threshold Behavior of Charge-Density Waves Pinned by Impurities

Abstract: A time-dependent mean-field theory of the nonlinear electric field response of a charge-density wave pinned by impurities is implemented. It is found that above a threshold electric field ${E}_{T}$, the charge-density wave moves with velocity $v\ensuremath{\propto}{(E\ensuremath{-}{E}_{T})}^{\frac{3}{2}}$. Some general discussion of the behavior as a function of dimension is included.

Electric field probes--A review

Abstract: Electric field probes consisting of a dipole antenna, RF detector, nonperturbing transmission line, and readout device have been implemented in a variety of ways. Three orthogonal dipoles are generally used in an E -field probe to provide a response which is nearly isotropic for all polarizations of the incident field. Diode detectors have been used with electrically short or resistivity loaded dipoles to produce very broadband devices (0.2 MHz to 26 GHz). Thermocouple detectors are used to provide true time-averaged data for high peak-power modulated fields. Optical fibers, together with a suitably modulated light source, may be used to form a wide-band nonperturbing data link from the dipole and detector to a remote readout. Application of E -field probes range from the measurement of fields in living animals exposed to nonionizing radiation to the measurement of fields in air for electromagnetic compatability or radiation safety purposes. Probes are available that can measure field strengths from less than 1 V/m to over 1000 V/m (rms).

Observations of large magnetospheric electric fields during the onset phase of a substorm

Abstract: An auroral substorm is a highly transient process which is triggered on auroral L shells and leads to an abrupt change of state in the nightside magnetosphere. Direct measurements of electric fields in the outer magnetosphere are of critical importance to understand the processes involved in sudden substorm enhancements. Shepard et al. (1980) reported direct measurements of electric fields from the GEOS 2 satellite at equatorial latitudes which showed 15 mV/m westward inductive electric fields in association with tail collapses. Similar direct electric field measurements of the westward inductive electric field at low latitudes from the ISEE 1 satellite during the onset phase of an auroral substorm are reported in the present investigation. The observations show a rapid inward magnetic field (westward electric field) motion near midnight at low or equatorial latitudes simultaneous with the sudden onset of auroral substorm enhancements near the foot of the satellite field line.

Monte‐Carlo simulation of electron properties in rf parallel plate capacitively coupled discharges

Abstract: Electron properties in a parallel plate capacitively coupled rf discharge are studied with results from a Monte‐Carlo simulation. Time averaged, spatially dependent electron distributions are computed by integrating, in time, electron trajectories as a function of position while oscillating the applied electric field at rf frequencies. The dc component of the sheath potential is solved for in a self‐consistent manner during the simulation. For conditions where the secondary emission coefficient for electrons from the electrodes is large, the electron distribution is spatially differentiated, being dominated by an e‐beam component near the electrodes while being nearly in equilibrium with the applied electric field in the body of the plasma. The dc component of the sheath potential is found to be a function of the ratio λ/d, where λ is the electron mean free path and d is the electrode spacing.

Semi-empirical equations for electron velocity in silicon: Part II—MOS inversion layer

Abstract: We present a simple model of inversion layer and accumulation layer mobilities in Si MOSFET's. The use of an effective normal field and a simple approximation for the temperature dependent quantum mechanically broadened channel layer width Permits the development of a versatile semi-empirical equation. This equation provides good agreement with electron mobility data in the literature as a function of normal electric field, temperature, substrate doping, and fixed charge density. Screening effects have considerable influence in the model. Subthreshold behavior is predicted with reasonable accuracy. The model is also applicable at high tangential fields where mobility is reduced due to hot-carrier effects.

Spatially varying polarization in water. A model for the electric double layer and the hydration force

Abstract: The formalism derived in the preceding paper is used to model the response of aqueous solutions to a spatially-varying applied electric field. It leads to a generalized theory of the electric double layer which explicitly takes into account the microscopic structure of the solvent. As the solvent polarization is allowed to vary depending on both the macroscopic electric field and the specific interactions at the surface, the result is more freedom in the structure of the electric double layer. We consider generalized expressions for the double-layer free energy, as well as the interaction of two double layers which include specific surface polarization. Such interaction consists of both classical double-layer repulsion and the strong, short-range ‘hydration force’.

S3‐2 measurements of the polar cap potential

Abstract: A total of 83 dawn-dusk, high-latitude passes of the S3-2 satellite has been analyzed for the period August through December 1976 to determine correlations between the cross polar cap potential Φpc and various solar wind-interplanetary magnetic field parameters. Hourly and 15-s averaged values of the interplanetary magnetic field components and hourly averaged values of the solar wind velocity were available for 68 of the passes. In 41 (27) of the cases studied, the interplanetary magnetic field had a southward (northward) component. Measured potentials ranged from 170 kV during a substorm to 12 kV during two periods of northward interplanetary magnetic field. Least squares fits to the data were performed in order to determine the dependence of the polar cap potential on four different electric field models derived from reconnection theory and other traditionally correlated solar wind-interplanetary magnetic field parameters. In each case, there is a residual polar cap potential of the order of 40 kV. This suggests a time delay in the relaxation of the potential when the interplanetary magnetic field turns northward and/or processes other than reconnection contribute to the polar cap potential. Total interplanetary magnetic field variance and solar wind speed were tested as filters on the data and found to have some significance. Comparisons with similar studies based on measurements from the Atmosphere Explorer and S3-3 satellites are discussed.

Polar cap electron DEnsities from de-1 plasma wave observations. Progress report

Abstract: Electric field spectrum measurements from the Plasma Wave Instrument on the Dynamics Explorer-1 spacecraft are used to study the local electron density at high altitudes in the northern polar cap region. The electron density is determined from the upper cutoff of whistler mode radiation at the electron plasma frequency. This technique typically gives the electron density with; an accuracy better than 12%.

An empirical electric field model derived from Chatanika radar data

Abstract: Plasma convection velocity observations obtained with the Chatanika, Alaska incoherent scatter radar have been used to prepare a quantitative empirical model of the convection electric field at auroral latitudes between 58°Λ and 75°Λ. Vector averaging of the individual days' data and smoothing across 2.5 hours of local time were used to reduce substorm perturbations. Tables of the vector electric field components at 300-km altitude have been prepared for moderately disturbed (Kp = 3) summer conditions. Resolution of the model is 0.5° of invariant latitude and one half hour of magnetic local time. The model field is asymmetric with the afternoon convection cell dominant in magnitude and spatial extent and corresponds to conditions in which the cross polar cap potential is approximately 70 kV.

High‐field drift velocity of electrons at the Si–SiO2 interface as determined by a time‐of‐flight technique

Abstract: We describe a new technique for the study of high‐field transport at semiconductor–insulator interfaces In this technique, we observe the time‐of‐flight of discrete charge packets introduced by a pulsed laser The packets drift in a region of uniform applied tangential field at the interface We present data on the room temperature drift velocity of electrons at the interface between (100) silicon and thermally grown silicon dioxide as a function of both tangential and normal electric fields We observe velocities near saturation of 89×106 cm/s at a tangential field of 4 V/μm and a normal field of 9 V/μm, and extrapolate to a saturation velocity of 92×106 cm/s independent of normal field This value is more than 40% higher than reported by early workers, and is close to the saturation velocity observed in bulk silicon

Solitary waves and double layers on auroral field lines

Abstract: Time stationary solutions to the Vlasov-Poisson equations for ion holes and double layers are examined along with particle simulations that pertain to recent observations of small amplitude electric field structures on auroral field lines. Both the time stationary analysis and the simulations suggest that the observed double layers evolve from holes in ion phase space. Multiple small amplitude double layers, as seen in long simulation systems, are observed to propagate past the spacecraft and may account for the acceleration of plasma sheet electrons to produce inverted-V precipitation.

Dawn‐dusk electric field asymmetry of the Io plasma torus

Abstract: The effects of a combined convection and corotation electric field across the Io plasma torus are considered. A dawn-to-dusk electric field E sub C will modify the orbits of charged particles shifting them toward dawn. The radial drift imposed by the perturbed orbits implies a local time-dependent modulation of low-energy ion and electron temperatures with particles hotter at dusk than at dawn. With E sub C approximately 4 mV/m, the orbits near 6 Jupiter radii would be shifted by approximately 0.2 Jupiter radius. Then the electron temperature would be 20% higher at dust than at dawn, an effect which could explain the local time asymmetry of EUV intensity found by the Voyager ultraviolet spectrometer. The source of the convection electric field is internal to the magnetosphere, and is attributed to the tailward escape of Iogenic and Jovian plasma beyond the Alfven surface.

Charge transport and trapping phenomena in off‐stoichiometric silicon dioxide films

Abstract: The electrical characteristics of off‐stoichiometric silicon dioxide films have been investigated. The off‐stoichiometric oxide films studied had an excess atomic silicon (Si) content in the range of 1%–6%. Raman spectroscopy and photoconductivity measurements indicate that the excess Si is present as amorphous Si islands or small crystallites embedded in silicon dioxide (SiO2) forming a two‐phase material. These films differ in structure from previously reported films where dual dielectric layers of stoichiometric SiO2 and Si‐rich SiO2 with ≥13% excess atomic Si were used. These dual dielectric films were observed to produce electron injection from contacting electrodes via the Si‐rich SiO2 layer into the SiO2 at lower average electric fields. This injection mechanism was believed to be due to localized electric field enhancement near the SiO2–Si‐rich SiO2 interface caused by the curvature of the tiny Si islands in the SiO2 matrix. The current versus voltage characteristics of the off‐stoichiometric oxid...

Transient electric and magnetic fields associated with establishing a finite electrostatic dipole

Abstract: We obtain analytical solutions in the time domain for the electric and magnetic fields associated with establishing a finite electrostatic dipole. We assume that a simple source current distribution, a square pulse of current, produces the dipole, and solve for the fields produced by that source current distribution using Maxwell’s equations. Salient features of the fields are discussed from a physical point of view. We outline a technique to determine in the time domain the electric and magnetic fields produced by any arbitrary time‐varying current propagating along a straight antenna, given the calculated fields due to a short square pulse of current.

On the drift mechanism for energetic charged particles at shocks

Abstract: The energy changes of energetic charged particles at a plane shock due to the so-called drift mechanism are analyzed by using the ''adiabatic treatment.'' The analysis shows that for a fast MHD shock, particles lose energy owing to acceleration (curvature) drift in the magnetic field at the shock with the drift velocity being antiparallel to the electric field, and they gain energy owing to gradient drift parallel to the electric field. It is shown that particles with pitch angles aligned along the magnetic field which pass through the shock tend to lose energy owing to acceleration drift, whereas particles with pitch angles nonaligned to the magnetic field gain energy owing to gradient drift. Particles that are reflected by the shock always gain energy. Slow-mode shocks may be similarly analyzed, but in this case curvature drifts give rise to particle energy gains, and gradient drifts result in particle energy losses.