对称强磁场产生装置设计及磁场仿真

在对称线圈上施加强脉冲电流,在脉冲电流的激励下,线圈中产生感应脉冲磁场,从而实现同极性磁场撞击.在撞击过程中,磁能会以一种波的形式激发出去,从而产生激磁波.激磁波是一种磁性波,其能量主要通过磁场的变化进行传递.利用有限元的方法对对称线圈的内部外部分别进行仿真,讨论并分析了磁场在空间和时间上的变化.     

Determination of the electric field in a Hall generator under influence of an alternating magnetic field

A method is described to calculate the electric field in a Hall generator under influence of an alternating magnetic field. The problem is divided into two separate problems, the first of which describes the Hall effect while the second gives the behaviour of the eddy currents. Each of these problems can be reduced to an integral equation, which is easily solved on a digital computer. The method is illustrated for a rectangular Hall generator.     

Resonant tunneling device with multiple negative differential resistance: Digital and signal processing applications with reduced circuit complexity

A new approach to obtain multiple peaks in the current-voltage characteristic of a resonant-tunneling (RT) device is demonstrated. The peaks are generated using only the ground state resonance of the quantum well rather than several states, as in conventional RT devices. The separation between the peaks is voltage tunable and also the peak currents can be made nearly equal, which is necessary to use the device in a variety of circuit applications. A functional device operating at 100 K, with two peaks in the I-V has been fabricated. The first practical demonstration of circuits for frequency multiplication by a factor of five, a three-state memory and a 4-bit parity generator, using a single functional RT device each, is also reported. The use of multiple-peak RT devices in these circuits results in an order of magnitude reduction in the number component per function over conventional techniques.     

Resonant tunneling in quantum heterostructures: electron transport,dynamics, and device applications

The current understanding of the resonant tunneling process of electrons in double-barrier (DB) diodes and in coupled quantum well structures is described. The authors examine the validity of the simple Fabry-Perot model in describing the electron transport in actual DB diodes. They then describe a picosecond laser study to clarify the dynamics of resonant tunneling, including the intrinsic time delay associated with the multiple reflection of electron waves. Lastly, they discuss both the current state and prospects of device applications for high-speed electronics and optoelectronics     

Compact modeling of the influence of emitter stored charge on thehigh frequency small signal AC response of bipolar transistors usingquasi-static parameters

A model involving only quasi-static parameters is proposed which is capable of modeling the influence of high frequency nonquasi-static stored charge distributions in the neutral emitter region on the small signal high frequency ac response of bipolar transistors. Quasi-static ac model parameters are completely determined from static charge distributions for arbitrary impurity profiles, thereby enabling high frequency behavior to be accurately deduced for realistic device structures without the need for high frequency numerical simulation or measurement. The proposed model provides quantitative information regarding the transition from quasi-static to nonquasi-static behavior of emitter stored charges. An existing equivalent circuit representation that accurately models the influence of the stored base charge, and which is suitable for SPICE simulations, is modified to include the impact of quasi-static charge distributions in the emitter region     

基于霍尔效应弱磁场测量装置的研制与应用

为了解决弱磁场强度测量困难的问题,基于霍尔效应开发了以线性霍尔元件为探头弱磁场测量装置。对磁场测量装置各部分电路模块进行了详细设计,并结合矩形线圈磁场分布特征进行了实测值与仿真理论值的对比分析。结果表明,测量结果与理论值具有较好的拟合程度,该装置测量精度为0.01 m T,测量范围为±10 m T,最大测量误差为0.29 m T,具有测量精度高、操作简单方便、设计成本低等优点,可应用于各类线圈弱磁场强度的检测及逐点测量实验中。     

RTD fluxgate: a low-power nonlinear device to sense weak magnetic fields

Fluxgate magnetometers have always been of interest to technical and scientific communities to sense weak magnetic fields (in the range of 10/sup -6/) with a resolution of 100 pT at room temperature. These devices find applicability in fields such as space, geophysical exploration and mapping, nondestructive testing, and assorted military applications. This article discusses the quantities affecting the RTD fluxgate performances, considerations on the design of an RTD fluxgate, and presents an magnetometer experimental prototype.     

超磁致伸缩换能器的磁场和温度场分析及其结构设计

本文针对超磁致伸缩换能器磁路设计进行分析,包括驱动器磁路设计、磁路分析与设计、偏置磁场设计、激励线圈设置、超磁致伸缩棒的处理等,结合超磁致伸缩换能器发热分析,通过研究换能器磁场有限元、伸缩棒磁场有限元、伸缩换能器温度场有限元、样机与测试、测试结果分析等内容,目的在于提高超磁致伸缩换能器运行的稳定性,提升系统运行的可靠性。     

Improvements to an electromagnetic near-field sensor forsimultaneous electric and magnetic field measurement

A sensor for simultaneous electric and magnetic field measurement has been described by M. Kanda (see ibid., vol.EMC-26, no.3, p.102-10, 1984). It relies upon measuring the voltage across precisely matched loads at opposite sides of a loop antenna. A modification to the theory is presented to account for unmatched loading of the loop. Measured results of wave impedance over a 10-400-MHz range demonstrate the accuracy of the modified theory as well as highlighting a novel calibration technique     

Effect of temperature on the thermodynamic density of states in a quantizing magnetic field

The dependence of the density of energy states (N _s ) on temperature in quantizing magnetic fields is studied. It is shown that, as temperature is increased, the Landau levels are blurred as a result of thermal widening and the quantities N _s are transformed into the density of states as in the absence of a magnetic field. The temperature dependence of the distribution of the density of energy states in high magnetic fields for semiconductors is considered using a mathematical model. It is shown that the continuous spectrum of density of states measured at liquid-nitrogen temperature is transformed into discrete Landau levels at lower temperatures. Mathematical simulation of the processes with the use of experimental data for the continuous spectrum of the density of states makes it possible to calculate the discrete Landau levels. Experimental results obtained for PbS are analyzed using the suggested model. The density of states at low temperatures is calculated from data on high-temperature N _s .     

Resonant length of longitudinal slots and validity of circuit representation: Theory and experiment

Pertinent theory for the design of longitudinal slot arrays is reviewed and its dependence on the dominant mode scattering off a single slot is pinpointed. The critical need to know resonant length versus slot offset is emphasized and the desirability of determining this information theoretically rather than experimentally is argued. Then method of moments solutions are used to calculate resonant length versus slot offset for given waveguide dimensions and frequency. These theoretical results are compared to new, carefully obtained experimental data. Agreement is found to be so good, it is concluded that one can dispense with the costly gathering of experimental input data when designing longitudinal slot arrays fed by standard rectangular waveguide. A critical look is taken at the validity of representing the longitudinal slot as a shunt element on an equivalent transmission line. This assumption is found to be more and more questionable as thebdimension is reduced. For quarter-height guide, an alternate design procedure is suggested as being more accurate.     

Losses in a high-temperature superconductor exposed to AC and DCtransport currents and magnetic fields

Summary form only given, as follows. The development of high-temperature superconductors (HTSs) is for the moment intensive and it is likely that HTSs will be used in different electric devices in a few years. In some of these devices that conductor will be exposed to both AC and DC transport currents and magnetic fields. In the design of electric devices, the power loss is indeed one of the most important parameters. Therefore there is a need of models that predict the power loss in an HTS under application-like conditions. In this paper, the authors present a semi-empirical model including a transport current and an applied magnetic field with both AC and DC components. The semi-empirical model is mainly based on the critical state theory. The results of the model are compared and found to be in good agreement with experimental results obtained with a calorimetric experimental set-up. The power loss was measured on a multi-filamentary Bi-2223 tape as function of transport current and applied magnetic field at a fixed temperature and frequency     

Thermoelectric power of the n-InSb in a transverse quantizing magnetic field at a large temperature gradient

The thermoelectric power of the n-type indium antimonide was studied in the transverse magnetic field (0–80 kOe) at T _aV =160 K and different temperature gradients. It was found that the electron component of the thermoelectric power at a small temperature gradient is consistent with the theory that takes into account the electron spin, whereas, for a large temperature gradient, the value determined by the variation of the Benedicks thermoelectric power in the magnetic field is added to this component.     

Reflection coefficient of a semiconductor superlattice subjected to a magnetic field

Propagation of magnetoplasma waves in a structure formed by periodically alternating semiconductor and dielectric layers is studied for the case where an external magnetic field is applied parallel to the layers; the waves traveling in the plane normal to the field are considered. Dispersion characteristics are calculated with the finiteness of the speed of light accounted for, and the features of the structure reflectivity are analyzed. It is demonstrated that the physical parameters and thicknesses of the layers composing the superlattice can be obtained from the frequency, angle of incidence, and magnetic-field dependences of the reflection coefficient.     

Spectrum of an electron in a quantum well in high inclined magnetic field and high transverse electric field

The energy and wave functions of localized electron states in a quantum well in a high magnetic field arbitrarily oriented with respect to the layers of the structure, and a high transverse electric field are studied. The situation where the quantum-confined energy and the Landau energy are close to each other is considered. The evolution of the spectrum with varying orientation of the magnetic field over the entire angle range is studied.     

基于磁流体磁体积效应的磁场与温度双参量传感器

为了实现磁场与温度的同时测量,提出并制作了一种基于磁流体(magnetic fluid,MF)磁体积效应的法布里-珀罗(Fabry-Perot,FP)腔与光纤布拉格光栅(fiber Bragg grating,FBG)级联的复合传感结构。注入空芯光纤(hollow-core fiber,HF)的MF液面与单模光纤端面形成的FP腔同时对磁场和温度敏感,与之级联的FBG只对温度敏感。通过同时监测FP腔特征峰与FBG布拉格反射峰的波长漂移,利用传感器磁场与温度敏感系数矩阵,同时获取温度与磁场信息。实验成功制备了初始腔长为56.1μm的FBG-FP温度磁场双参量传感器,磁场与温度灵敏度分别达到了16.21 pm/Oe和9.96 pm/℃,具有体积微小、结构简单、成本低等特点。该传感器可解决常规光纤磁场传感器的磁场-温度交叉敏感问题。     

The temperature dependence of the thermopower of the InSb Corbino disc in a quantizing magnetic field

Thermopower of the Corbino disc made of InSb with n ₇₇ = 2 × 10¹⁴ cm^?3 in a transverse magnetic field as high as 30 kOe at temperatures of 60, 67, and 80 K is studied. It is established that the diffusion fraction of thermopower in a quantizing magnetic field rises according to the power law H ^2.2 at all mentioned temperatures. By the magnitude of saturation thermopower α_xx(∞) in a high field, the scattering mechanism of charge carriers is determined. It is established that in a temperature region of 60–80 K, the electrons are scattered by acoustic phonons.