精确测量微安直流的全数字化磁调制器

为满足微安级直流信号精密测量的需求,设计研制一种精确测量微安直流的全数字化磁调制器。其通过将激励端与输出端电压转换成数字信号,再进行傅里叶分析,矢量法调零与比例系数校正后实时获取直流测量值。测量结果表明,在测量范围为5μA～1 000μA时,精度可达到0. 5%,线性误差优于2×10~(-4),且有效抑制激励源频率与幅值变化导致的测量误差。     

MQAM调制器的设计与实现

文中提出了一种多电平正交振幅调制器(MQAM)的设计与实现方法。该调制器由纠错编码部分、脉冲成形滤波器和混频器构成。实践证明,本设计可在单片FPGA中实现DAVIC协议中所建议的MQAM(M=16,64,256)调制器。该设计可在数字电视机顶盒(STB)内作为实现交互电视(iTV)的主体功能模块,具有较高的实用价值。     

Design of a SiGe-Si quantum-well optical modulator

A light modulator consisting of modulation-doped SiGe-Si multiple quantum wells integrated in a silicon-on-insulator waveguide is designed. The device is based on the electrorefractive effect due to the variation of holes density in the SiGe wells, induced by applying a reverse bias on a PIN diode. This mechanism is simulated by numerical calculations of the hole distribution coupled with the optical guided mode propagation characteristics. The mode effective index variation of TE-polarized light at the 1.31-/spl mu/m wavelength can then be obtained as a function of the applied bias. The influences of the structure parameters such as the thickness and the doping level of the doped barrier layers or the number of SiGe wells is analyzed thanks to a design of experiment method. The optimization gives an effective index variation of 2.10/sup -4/ for an applied bias voltage of 6 V. To obtain optical intensity modulation, this structure has to be included in a Fabry-Perot cavity. The modulation performances are analyzed.     

The higher harmonics of the electromagnetic moments of a magnetoelectric reducer

In a correctly designed magnetic reducer, the electromagnetic moments depend on the torque angles, with the dependence being near-sinusoidal. If the active zones have a nonoptimal geometry, the electromagnetic moments have high-frequency oscillations caused by the reaction moments, resulting in discrete locking or sticking of the fixed rotors. Under unfavorable conditions, the amplitudes of the pulsations may be comparable with the maximum or tilting electromagnetic moment value. The electromagnetic moments of a magnetoelectric gear reducer (MER) are calculated by the energy method based on trigonometric-series expansion of the specific magnetic conductance of the air gaps and the MMF of the magnets. For this purpose, integral expressions are found for the magnetic field energies in the air gaps which depend on the rotational positions of the rotors with respect to the fixed stator magnets. For arbitrary selected harmonics of the magnetic conductance of the air gaps and the magnets’ MMF, the conditions are determined for the orders of the above harmonics and the number of the cogs and poles at which the integrals for the magnetic field energy will be different from zero. Such an approach allowed deriving equations for the basic electromagnetic moments and the concomitant stray moments. If the found conditions are not met, the extraneous harmonics of the electromagnetic moments are eliminated. Selection of a number of modulator rods equal to a prime number is a radical means of eliminating higher harmonics of the electromagnetic moments. If a prime number of the rods cannot be selected, such numbers of the stator pole pairs should be selected at which the presence of higher harmonics of the electromagnetic moments is possible at the highest order values of the harmonics of the magnetic conductance of the air gaps and the MMF of the stator and rotor magnets.     

Fast control of current of a pulse-width modulator

A fast system of controlling a current in an active inductive load by a pulse-width modulator is proposed. For maximum fast control, a dead-beat control constructed without transformation of coordinates is used. A synthesis method of regulator parameters is given.     

Magnetic field gradient system for nuclear magnetic resonance microimaging

In this study we present an orthogonal magnetic field gradient system for nuclear magnetic resonance (NMR) microimaging applications. The construction details are given for a prototype assembly for proton microscopy inside a 50-mm vertical bore magnet, which is designed to fit into a commercial 300-MHz NMR probe. This system has been used to acquire images of the human spinal cordin vitro. Its performance has been evaluated and compared to that predicted by computer simulation.     

A single-phase inverter with a deadbeat regulator of a pulse-wide modulator

The structure of a control system for a pulse-wide modulator (PWM) of a single-phase voltage inverter is proposed; this control system comprises a deadbeat regulator for inducing transient processes with a finite duration in the near vicinity of an equilibrium position. A method for synthesizing the parameters of the regulator for an inverter that includes an active-inductive load with an output voltage feedback is described. Results of modeling the processes, which show a higher efficiency of the deadbeat regulator, are presented.     

Magnetic instability of ac multifilamentary superconductors in spatially distributed magnetic field

Alternating current (ac) superconducting machines such as superconducting generators, transformers, or resistive current limiters need large‐current‐capacity conductors. These conductors are generally fabricated as multistrand cables stacked with multifilamentary NbTi superconductors whose current capacity is a few tens of amperes. ac quench current degradation has often been observed in ac use of such multistrand cables. Several reasons for this degradation have been pointed out: nonuniformity of each strand current, mechanical disturbances, thermomagnetic instability, and ac losses. However, it has not as yet been overcome. Since the angle between the strand axis and the cable axis changes along the cable axis in multistrand cables, the strands are exposed to a spatially (axially) distributed magnetic field, which has longitudinal and transverse components changing periodically due to multiple cabling. This paper mainly discusses the thermomagnetic instability due to the distributed transverse magnetic field, which was compared with the self‐field instability and the longitudinal field instability experimentally and theoretically. It was confirmed that the ac quench current degradation due to the distributed transverse field could be induced by the following: nonlinear E–j characteristic, strong dependence of E–j characteristic on magnetic field in low field region, uniformity of the axial current profile inside the superconductor with the high resistive matrix, and the poor thermal diffusion of CuNi/NbTi composites. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 45–55, 2000     

Contribution to the modeling of a non-ideal Sigma-Delta modulator

One major issue facing the design and the simulation of complex circuits, such as Sigma-Delta modulators (ΣΔM), is the relatively large computing-time; required when using transistor level based simulators. Hence, high-level system modeling is suitable to achieve a time-efficient IC design. In this scope, the aim of the present work is to develop an enhanced model for a switched-capacitor second order sigma delta modulator. Besides the numerous effects, already included in the standard models, many additional non-idealities aspects have been taken into consideration. Namely, the DC nonlinearity behavior of both: the operational amplifier (OP-AMP) and the switches ON-resistance. The obtained model permits, thus, more accurate prediction of the relative signal-to-noise ratio (SNR), compared to the standard one.     

RV减速器的模态仿真及实验

RV减速器是工业机器人的核心零件,针对我国生产的减速器寿命短、噪声大等缺点,研究其动态特性意义重大。模态特性是研究动态特性的基础,是研究的第一步。论文建立有限元模型,对RV减速器中的主要部件进行模态仿真,仿真结果和实验结果相差不到5%,在误差范围内,验证了仿真结果的可靠性以及有限元模型的准确性;用Bush单元简化轴承,施加约束后对整体进行模态分析,前三阶固有频率远大于啮合频率,说明工作状态时在外部激励下结构共振的可能性小,为后续研究结构的动态特性提供参考。     

Design of a phase-shifting optical feedback interferometer using anelectrooptic modulator

A laser sensor using optical feedback interferometry has been designed to measure displacements up to several micrometers. For this purpose, a lithium niobate crystal generates a phase shift in order to modulate at a frequency of 580 kHz the optical path difference between the sensor and the target. This setup has been calibrated by means of a commercial optical fiber sensor. The overall accuracy resulting is better than 65 nm for a 1-kHz sinusoidal motion of the target at 10 cm away from the sensor     

圆筒式永磁联轴器磁场仿真分析及结构优化设计

为确保乏燃料后处理厂混合澄清槽搅拌装置的永磁联轴器长期安全可靠运行,对永磁联轴器进行磁场仿真分析及结构优化设计。采用有限元方法建立三维磁场仿真模型,建模过程充分考虑联轴器的实际运行工况。首先,考察磁极对数、磁极厚度、磁场气隙、磁转角对磁转矩的影响。其次,通过温度场仿真分析考察转速对联轴器温升的影响。最后,以降低联轴器的隔离套温升为目标,对其进行结构优化设计并进行仿真分析。结果表明:优化结构的隔离套温升得到明显减小。控制联轴器温升可有效降低永磁联轴器退磁失效风险。研究成果可为同类型联轴器设计提供参考。     

Constraints on constant-input oscillations of a bandpass sigma-delta modulator structure

This paper presents sets of conditions on the parameters of bandpass sigma–delta modulators for which the oscillations of the state variables remain bounded within a specific square of the state space. The conditions are associated with areas in the parameter space and the system dynamics is illustrated for parameter sets showing examples of typical oscillations, both those which are and those which are not constrained to the specified square. © 1997 by John Wiley & Sons, Ltd.