An exact small-signal analysis of the interaction of two electron streams in a finite longitudinal magnetic field

Using the mathematical field analysis of a companion paper in this issue, solutions are found for the wave interactions occurring in several different configurations of drifting electron beams in a longitudinal magnetic field. First, wave interactions are found for both single and double beams of infinite extent. Next, single and double beams completely filling a cylindrical waveguide are analyzed. Finally, examination is made of single and double beams which only partially fill the waveguide. The resulting wave interactions are described with ω-β (dispersion) diagrams. Since only the small-signal approximation is made, space-charge waves, cyclotron waves, and waveguide waves are all present in this analysis.     

Impedance of a finite insulated cylindrical antenna in a cold plasma with a longitudinal magnetic field

A variational formulation is developed for the impedance of a finite cylindrical antenna embedded in a dielectric cylinder, which is surrounded by a magnetoionic medium (cold electron plasma) with the static magnetic field impressed in a direction parallel to the antenna axis. Closed form expressions are obtained in the limit of low frequencies, and for short antennas in a uniaxial medium. The impedance of a short antenna is nearly the same as for an assumed triangular current distribution, except that further resonances are observed in the vicinity of the gyro frequency, where the antenna becomes electrically long. These resonances may be shifted to frequencies exceeding the gyro frequency in the presence of an insulating layer around the antenna. For very thin insulating layers the wave number of the variationally approximated current distribution is to the first order equal tosqrt{epsilon_{1}} k_{0}(epsilon_{1}is the leading diagonal element of the permittivity matrix), where the gyro frequency may be both smaller or larger than the plasma frequency. However, this approximation does not apply to current distributions along the insulated antenna. The present calculations are also compared with earlier work on antenna impedances.     

Fission of longitudinal autosolitons in InSb in a magnetic field

The behavior of longitudinal autosolitons in InSb in a weak magnetic field was studied. It is shown experimentally that a weak longitudinal magnetic field affects significantly the behavior of longitudinal autosoliton in InSb samples. In all samples, sharp changes in the current due to fission of longitudinal autosoliton were observed for certain values of a magnetic field. It was found that the magnitude of initial autosoliton cur-rent took a different stable value under the effect of a magnetic field. The initial value of the autosoliton current is recovered if a magnetic field of opposite orientation is applied to the sample.     

A small-signal field theory analysis of crossed-field amplifiers applicable to thick beams

Various authors have presented analyses of crossed-field amplifiers. Generally, these analyses have dealt with very thin electron beams in the presence of crossed-fields or with beams in which the bulk ac charge density within the beam has been neglected. It is the purpose of this paper to develop a field-theory analysis which is applicable to both thick or thin beams and which includes the effect of space charge. In place of the usual approximate match at the input boundary plane, a rigorous variational technique is presented, which considers the effect of the cutoff waves on the amplitudes of the propagating waves. This enables one to solve the input boundary problem for the first time insofar as the amplitudes of the propagating waves are concerned, without determining the individual amplitudes of the cutoff waves implicitly. As opposed to the usual approximate match, which is only valid for a thin, unmodulated entering electron stream, this variational method is valid for both thick and thin beams, as well as unmodulated or modulated beams entering a crossed-field slow-wave interaction region or entering a crossed-field drift region. The paper presents propagation constants obtained for thick beams based on the author's model. The variational procedure, which is a valid technique for other models as well as other types of beam devices, has been applied to one numerical case involving a thin beam and the results are compared with the results of the usual approximate match. A modification of the complex amplitudes of the excited waves, even in the case of thin beams, is noted.     

A technique for accurate magnetic resonance imaging in the presence of field inhomogeneities

A technique for producing geometrically accurate magnetic resonance images (MRIs) with undistorted intensity in the face of high levels of static field inhomogeneity arising from either source is presented. The technique requires the acquisition of two images of the same object with altered gradients. On the basis of a knowledge of these gradients it employs an automatic postprocessing step that exploits some invariant characteristics of the distortions to produce a rectified image from the two acquired images. No phantom imaging is involved and no operator interaction is required. The technique is theoretically justified and compared to other techniques, and experimental results that show that the technique works are presented. The improved accuracy in geometry and intensity may improve reliability of stereotactic surgery, may enhance the feasibility of both clinical and industrial imaging via external fields, and may increase the resolution of microscopic imaging.     

Impurity absorption of light in confined systems subjected to a longitudinal magnetic field

The multiphonon-assisted impurity absorption of light is analyzed theoretically. The bound state is described in terms of the zero-radius potential model. The obtained frequency dependence of the light absorption coefficient and the full widths at half maximum (FWHMs) of the absorption lines are compared with experimental data.     

A new parameter extraction technique for small-signal equivalentcircuit of polysilicon emitter bipolar transistors

We propose a new parameter extraction method for advanced polysilicon emitter bipolar transistors. This method is based on the predetermination of equivalent circuit parameters using the analytical expressions of de-embedded Z-parameters of these devices. These parameter values are used as initial values for the parameter extraction process using optimization. The entire device equivalent circuit, containing RF probe pad and interconnection circuit parameters extracted by test structures, is optimized to fit measured S-parameters for eliminating de-embedding errors due to the imperfection of pad and interconnection test structures. The equivalent circuit determined by this method shows excellent agreement with the measured S-parameters from 0.1 to 26.5 GHz     

Elimination of the electron-phonon interaction in superlattices in a quantizing magnetic field

The energy and wave-vector conservation laws impose rigid constraints on the possible electron-phonon interaction processes in a superlattice immersed in a quantizing magnetic field directed along its growth axis. If the width of the Landau subband is smaller than the maximum energy of an acoustic phonon in the superlattice, single-phonon intraband scattering becomes impossible for all electron states in the subband considered. Therefore, the phonon contribution to the electron scattering processes can become negligible in superlattices with a large period in the presence of a quantizing magnetic field. Fiz. Tekh. Poluprovodn. 32, 730–732 (June 1998)     

A two-dimensional theory of a carcinotrode developed with allowance for the finite intensity of the focusing magnetic field

A kinematic theory of a backward-wave tube with self-modulated emission (carcinotrode) is formulated with allowance for the effect of the focusing magnetic field. Using the method of successive approximations and the dispersion equation technique, the starting conditions for the carcinotrode in the general case and in the two-wave approximation (the synchronous regime and the new cyclotron resonance regime) are obtained.     

Impedance of a finite insulated antenna in a cold plasma with a perpendicular magnetic field

A variational formulation is developed for the impedance of a finite strip antenna embedded in a planar dielectric slab which is surrounded by a magnetoionic medium (cold electron plasma) with a static magnetic field impressed in a direction perpendicular to the antenna surface. Closed form expressions are obtained in the limit of low frequencies, and for a short antenna in a uniaxial medium. The impedance becomes large at the plasma frequency, near the upper hybrid resonance frequency, and further resonances are observed near the gyro-frequency if the gyro-frequency exceeds the plasma frequency. The reactance of a short antenna is inductive at low frequencies, but becomes capacitive as the thickness of the insulation around the antenna is increased. For very thin insulating layers the wave number of the variationally approximated current distribution exceedssqrt{sqrt{epsilon_{1}} sqrt{epsilon_{3}}} k_{0}(epsilon_{1}andepsilon_{3}are the two diagonal elements of the permittivity matrix), whereepsilon_{1}andepsilon_{3}may have positive or negative real parts. However, this approximation does not apply to current distributions along an insulated antenna. The present calculations are also compared with earlier work on antenna impedances.     

A simple technique for longitudinal mode selection

Single longitudinal mode operation of pulse-pumpedQ-switched Nd:YAG and ruby lasers has been achieved by providing an intracavity mode-selecting resonator that contains the laser's active medium.     

A quasi-one-dimensional analysis of small-signal current gains in lateral transistors

A small-signal analysis of lateral p-n-p transistors has been made using a quasi-one-dimensional model. This model consists of a lateral p-n-p intrinsic transistor section and a vertical p-n-n⁺-p parasitic transistor section. The effect of the retarding electric field of the n⁺subdiffused layer is incorporated explicitly into the model. Besides, the field-dependent nonunity emitter efficiency of lateral transistors has also been taken into account. From the solutions of continuity equations in the base regions, closed-form expressions for small-signal current gains are obtained in terms of an ac field factor which is defined by the geometry and doping profile of the device. Frequency dependence of current gains evaluated from this analysis compares favorably with the results from an earlier two-dimensional analysis. The simplicity of the model and its reasonably good accuracy are expected to be helpful in the modeling of lateral transistors used in linear integrated circuits.     

The effect of a longitudinal magnetic field on electronic intersubband transitions in asymmetric heterostructures

Infrared absorption spectra are calculated for electronic intersubband transitions in asymmetric heterostructures subjected to a longitudinal magnetic field. The systems discussed include a single quantum well in a transverse electric field, a “stepped” quantum well, and a double well with tunnel-coupled excited levels. The longitudinal magnetic field causes collisionless broadening of the absorption peaks (because the effect of the magnetic field on the dispersion law of an electronic state varies from state to state, which modifies the transitions between them) and absorption of normally incident light (due to changes in the selection rules). Fiz. Tekh. Poluprovodn. 31, 1121–1125 (September 1997)     

单频He-Ne激光器中纵向非均匀磁场的应用

作者用高气压加纵向非均匀磁场的方法作了一系列单频输出的试验，成功地试制出了两台一米单频He-Ne激光器。本文报导了这些试验的数据和测试结果，并从理论上作了初步探讨．     

A novel finite-element formulation for the analysis of the energylevels of a quantum cavity in a magnetic field

A novel finite-element formulation for the analysis of the energy levels of a two-dimensional quantum cavity in a magnetic field is proposed. Our formulation is based on both a variational and Galerkin methods which, when combined with a finite-element method, lead to eigenvalue problems characterized by either real or Hermitian matrices contrary to algorithms proposed in the past. These eigenvalue problems can then be solved quite efficiently on a computer using standard library packages. Also, it is confirmed that the results obtained here are independent of the choice of gauge     

Effects of a finite axial magnetic field on the beam loading of a cavity

The effect of a finite axial magnetic field on the beam loading of a cavity is evaluated. The calculation extends Branch's classic paper on ballistic bunching in that both the conductive and susceptive components of the beam-loaded admittance are computed, for general values of axial magnetic field. Also included is a comparison of the analytic formulation with a two-dimensional particle-in-cell simulation. This paper suggests that the finite axial magnetic field used in linear beam tubes (typically exceeding 1.5 /spl times/ the Brillouin field) would only modify the beam-loaded admittance by about 20%, from that computed under the assumption of an infinite axial magnetic field.     

A novel frequency-domain small-signal analysis of resonant power converters

A frequency-domain small-signal analysis of resonant power converters is presented. In this analysis, the load presented to the ac side of the rectifier is modeled as a time varying resistor. Using conversion matrix techniques and an iterative procedure to find the magnitude and phase of the time-varying resistor, the transfer functions of the converter can be obtained fast and accurately. An advantage of this approach is that the analysis can be carried out with the load represented in the frequency domain. This is a significant advantage when dealing with complex (e.g., plasma) loads where only measured small-signal impedance data may be available. An example demonstrating the accuracy of the method is presented.