一种基于起伏地形与辐射电场分布相似性的指纹辅助定位方法仿真研究

在使用基于接收信号强度指示器（received signal strength indicator, RSSI）的指纹定位的过程中,通常要在离线阶段构建它的场强地图. 然而,在构建场强地图时,山区地形的复杂性常常导致我们难以确定测量区域的位置. 针对如何定位这些缺少位置信息的测量区域问题,文中提出了一种基于起伏地形与辐射电场分布相似性的定位方法. 该方法利用电场场值在发射源附近快速衰减的变化趋势与地形起伏高度降落的变化趋势相近,以及辐射电场的干涉条纹形状与地形轮廓相似这两种规律,以二维相关系数表征二者相似度,运用模板匹配算法,有效确定了测量区域在地理环境中的位置. 以二维随机粗糙面模拟起伏地形,通过地形中不同位置、不同大小的模板区域、不同发射天线高度和不同地形地貌下的多角度仿真实验,以重叠率作为性能评价指标,验证了方法的有效性.     

Resonance propagation of electrons through three-barrier structures in a two-frequency electric field

The solution of the Schrödinger equation that describes resonance transitions between three equidistant quantum levels in asymmetric three-barrier resonance-tunnel structures in a high one-frequency electric field is extended to the case of differently separated levels and a two-frequency field, with the frequencies corresponding to resonance transitions in each of the coupled quantum wells. It is shown that, in the conditions of coherent electron transport, irrespective of the parameters of the structure, for any amplitude of the high resonance field in one well, there exists an amplitude of the resonance field in the other well such that the structure is absolutely transparent and most electrons (in the limiting case, all electrons) incident on the upper resonance level can emit two photons with different frequencies and leave the structure through the lower level with no intermediate interaction with phonons. The probability of the transitions substantially depends on the amplitudes of the fields and does not depend on the phase difference between the fields. It is found that the possibility exists of almost complete blocking of resonance transitions in one of the wells by a high-frequency field in the other well.     

Optical field distribution in close-confined laser structures

An experimental and theoretical study has been made of the radiation patterns from GaAs lasers with a "close-confined" structure. The lasers were grown by liquid-phase epitaxy and consisted of a p+ - p-n structure with Al in the p+ region. Photometric measurements were made of the intensity distribution at the emitting facet (microscope observations) and the radiation pattern in a plane perpendicular to the junction. The electromagnetic field distribution in the vicinity of the p-n junction and the radiation pattern were calculated by solving the wave equation for a three-layer structure with complex dielectric constants in each layer. The theory predicts enhanced confinement of the radiation by the increased dielectric discontinuity due to the heterojunction, in agreement with the low lasing threshold and high efficiencies of the close-confined diodes. Another consequence of the theory is that as the thicknessdof thepregion of the cavity is increased, higher order modes can propagate with efficiences much greater than in ordinary lasers without the heterojunction. The third mode, corresponding to three intensity maxima along a line perpendicular to the junction, was observed ford = 5 mu. The good agreement found between the observed and calculated radiation patterns indicates that confinement of the radiation by dielectric discontinuities is an important factor in explaining the low-threshold currents found in close-confined lasers.     

Calculations of the current-voltage characteristics of electroformed MIM structures,assuming a normal distribution of filamentary radii

Voltage-controlled differential negative resistance (VCNR) is known to occur in many electroformed metal-insulator-metal (MIM) structures. Current-voltage characteristics obtained from electroformed MIM devices can be derived using a model in which conduction is assumed to take place through an array of filaments spanning the two electrodes. The model assumes that conduction through the filaments is ohmic but deviates from this as filaments rupture due to Joule heating. Previous results based on filamentary models have been obtained by assuming that the filament resistances are distributed normally or according to some alternative distribution. Here we consider a filamentary model in which the radii of filaments are taken to be normally distributed. The corresponding current-voltage characteristics are derived and found to be typical of those obtained experimentally.     

Resonant interaction of electrons with a high frequency electric field in two-barrier structures

The frequency dependences of the small-signal dynamic conductivity of symmetric and nonsymmetric two-barrier heterostructures are calculated in a one-electron approximation. Special attention is focused on the case of electron tunnelling through the upper minibands. In the approximation of high-barrier power (width), an analytic expression is obtained for the dynamic conductivity of a two-barrier resonance-tunnel structure that agrees with a rigorous calculation. It is shown that (a) the dynamic conductivity increases as the fourth power of the barrier width, (b) quantum transitions with an even change in the level number are forbidden, and (c) the dynamic conductivity is inversely proportional to the cube of the frequency if the separation between the levels varies with frequency in a way such that the resonance condition is always satisfied. The maximum possible intensity of the radiating transitions of twobarrier heterostructures are calculated as a function of the quantum numbers of the working levels under conditions such that the supply current density and the characteristic time for breakup of the coherence by phonon scattering are constant. It is shown that the intensity increases significantly if, for example, the fourth level of the structure, rather than the ground state, is used as the working level. Fiz. Tekh. Poluprovodn. 31, 201–208 (February 1997)     

Phase modulation of mid-infrared radiation in double-quantum-well structures under a lateral electric field

The modulation of polarized radiation by GaAs/AlGaAs structures with tunnel-coupled double quantum wells in a strong lateral electric field is studied. The spectra of the variation in the refractive index under a lateral electric field in the vicinity of the intersubband resonance are experimentally investigated.     

Potential distribution for a spheroidal cell having a conductivemembrane in an electric field

When a cell is situated in a uniform electric field, the field is modified due to the relatively low conductance of the cell membrane compared to that of the surrounding fluids. In certain cases, such as in the estimation of internal and external electrokinetic forces, one requires a means of estimating the magnitude of the electric field inside and outside the cell. Most treatments consider the case when the membrane has zero conductivity, or the case of only a spherical cell. The authors solve Laplace's equation for the electric potential distribution inside and outside a cell having a prolate spheroidal shape and having a membrane with a finite, nonzero conductivity     

Energy distribution of emitted electrons from electroformed MIM structures: the carbon island model

The electrons emitted from an electroformed metal island metal (MIM) device have a broad energy distribution with an FWHM of more than 2eV. The emission is thermionic from potentials somewhere between the electrodes. Islands, as detected by potentiography in an STM, are assumed to be the emitting spots. This model is able to describe all features of electron and photon emission, as well as electrical properties of electroformed MIM devices. It involves hot electrons in the lattice of small carbon islands embedded between carbon electrodes.     

Electrical characterization of AlN MIS and MIM structures

Aluminum nitride (AlN) thin films have been deposited on p-Si[100] and Mo-Si[100] substrates. The sputter deposited Mo was polycrystalline, predominantly showing a [110] orientation. Thin AlN films were grown under different process conditions in a physical vapor deposition (PVD) system to attain highly textured polycrystalline films as well as close to amorphous films. MIS and MIM structures were fabricated and electrical properties such as the dielectric constant, leakage current, and high-frequency behavior were investigated. It is found that the dielectric constant is 10 and does not change with the crystallinity of the films. High-frequency measurements up to 10 GHz show no frequency dispersion of the capacitance. The leakage current stays relatively constant between films and is believed to be Poole-Frenkel controlled. Capacitance-voltage (C-V) measurements for MIS structures revealed the presence of charges in the interface layer between the substrate and the dielectric film. The temperature dependence of the capacitance has also been studied.     

An analytical expression for the electric field in MSM structures

In this work the conformal mapping is used to determine an analytical expression for the electric field in MSM structures. The expression simplifies the analysis of optically generated carriers transport, i.e. the determination of the response of the MSN photodetectors. It can also be useful in the analysis of MSM electrooptical modulators operation.     

二维光子晶体中场的分布

为了了解电磁波在光子晶体中的传输特性,用MATLAB与时域有限差分法把电磁波在真空与光子晶体中的传播实时可视化,并给出了场的空间静态分布.数值模拟的结果表明,禁带中的波被光子晶体控制,其能量分布在介质柱中,并观察到了电磁波局域化现象.     

加载横电磁传输室中的电场分布计算

用“准静脉法”研究了当工作频率远低于截止频率时,放置于横电磁传输室中的被测物体中的电场分布。文中使用的是有限差分法,给出了在三维空间中不同介质交界面上拉普拉斯方程的差分格式。计算结果表明当把ＥＴＵ放入ＴＥＭＣｅｌｌ的中心时,ＥＵＴ横截面上的电场分布是均匀的。     

Diagnostics of the hot-hole distribution function in quantum wells in a strong electric field

Modulation of the fundamental absorption edge by a high lateral electric field in a p-type In_0.21Ga_0.79As/GaAs heterostructure with quantum wells was studied at 4.2 K and electric fields as high as 1.9 kV/cm. The field-induced change in the symmetric part of the hole distribution function was measured.     

Interfacial charges and electric field distribution in organic hetero-layer light-emitting devices

The electric field distribution in organic hetero-layer light-emitting devices based on N,N^′-diphenyl-N,N^′-bis(1-naphtyl)-1,1^′-biphenyl-4,4^′-diamine (NPB) and 8-tris-hydroxyquinoline aluminium (Alq₃) has been investigated under different bias conditions using capacitance–voltage measurements. Although this method yields primarily information on the differential capacitance, the data give clear evidence for the presence of negative interfacial charges with a density of 6.8×10¹¹e cm⁻² at the NPB/Alq₃ interface at large reverse bias. This leads to a jump of the electric field at the interface and a non-uniform field distribution in the hetero-layer device.     

Angular phase distribution of the field of an electric dipole in a hot magnetoplasma

The angular distribution of the phase of the fields of an electric dipole with and without a sheath in a hot magnetoplasma is calculated. Like the amplitude distribution of the field, the phase distribution can also be used for estimating the electron temperature.     

Investigation of electronic transitions in coupled-quantum-well structures with a built-in electric field by photoreflectance spectroscopy

Room-temperature photoreflectance spectra of coupled-quantum-well heterostructures with a built-in electric field are measured. The optical transition energies are determined and their dependences on the well width and the barrier thickness are examined. The experimental results are compared with the calculated energies of electron-hole transitions. Good agreement between calculations and experiment is found for narrow wells; in the case of wide wells, optical transitions are associated with groups of several closely spaced electron-hole transitions.     

A model for the electric field in lightly doped drain structures

A semi-quantitative model for the lateral channel electric field in LDD MOSFET's has been developed. This model is derived from a quasi-two-dimensional analysis under the assumption of a uniform doping profile. A field reduction factor and voltage improvement, indicating the effectiveness of an LDD design in reducing the peak channel field, are used to compare LDD structures with, without, and with partial gate/drain overlap. Approximate equations have been derived that show the dependencies of the field reduction factor on bias conditions and process parameters. Plots showing the trade-off between, and the process-dependencies of, the field reduction factor/voltage improvement and the series resistance are presented for the three cases. Structures with gate-drain overlap are found to provide greater field reduction than those without the overlap for the same series resistance introduced. This should be considered when comparing the double-diffused and spacer LDD structures. It is shown that gate-drain offset can cause the rise of channel field and substrate current at large gate voltages. This offset is also found to be responsible for nonsaturation of drain current. The model has also been compared with two-dimensional simulation results.     

High resolution potentiometry of planar electroformed MIM structures

Many attempts have been made to detect the current carrying filaments in electroformed metal-insulator-metal (MIM) structures (Pagnia and Sotnik 1988, Pagnia 1990). Transmission and scanning electron microscopes have been used without real success. Even experiments with the scanning tunnelling microscope (STM) could not definitely detect the filaments. We have mapped the potential distribution on an electroformed planar MIM diode (gold on quartz glass) with an STM and found usually only one (sometimes a few) sharp potential drop(s) in the microslit.     

准分子激光器中张氏面型电极的电场仿真研究

为了获得准分子激光器高脉冲能量输出,采用张氏面型电极的理论,设计了一套能产生大面积均匀电场的紧凑型电极。通过ANSYS软件数值仿真获得了电极表面电场分布,并与紧凑型张氏面型电极的理论计算结果进行了对比验证;分析了紫外火花预电离结构对电极放电的影响,并进行了电位和电场分布仿真。结果表明,预电离板的存在直接影响了电极之间的电位和电场分布;电场仿真结果解释了预电离板的顶端与阳极形成放电的原因。该研究为大面积辉光放电电极设计提供了更深入的理论支持。