Effect of welding current and speed on occurrence of humping bead in high-speed GMAW

The developed mathematical model of humping formation mechanism in high-speed gas metal arc welding （GMAW） is used to analyze the effects of welding current and welding speed on the occurrence of humping bead. It considers both the momentum and heat content of backward flowing molten jet inside weld pool. Three-dimensional geometry of weld pool, the spacing between two adjacent humps and hump height along humping weld bead are calculated under different levels of welding current and welding speed. It shows that wire feeding rate, power intensity and the moment of backward flowing molten jet are the major factors on humping bead formation.

A survey of high-speed high-resolution current steering DACs

Digital to analog converters(DAC)play an important role as a bridge connecting the analog world and the digital world.With the rapid development of wireless communication,wideband digital radar,and other emerging technologies,better performing high-speed high-resolution DACs are required.In those applications,signal bandwidth and high-frequency linearity often limited by data converters are the bottleneck of the system.This article reviews the state-of-the-art technologies of high-speed and high-resolution DACs reported in recent years.Comparisons are made between different architectures,circuit implementations and calibration techniques along with the figure of merit(FoM)results.

Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Current status and reflection on the development of high-speed maglev transportation

Purpose–High-speed maglev technology can address the issues of adhesion,friction,vibration and highspeed current collection in traditional wheel-rail systems,making it an important direction for the future development of high-speed rail technology.Design/methodology/approach–This paper elaborates on the demand and significance of developing high-speed maglev technology worldwide and examines the current status and technological maturity of several major high-speed maglev systems globally.Findings–This paper summarizes the challenges in the development of high-speed maglev railways in China.Based on this analysis,it puts forward considerations for future research on high-speed maglev railways.Originality/value–This paper describes the development status and technical maturity of several major high-speed maglev systems in the world for the first time,summarizes the existing problems in the development of China’s high-speed maglev railway and on this basis,puts forward the thinking of the next research of China’s high-speed maglev railway.

A Statistical Method for Characterizing CMOS Process Fluctuations in Subthreshold Current Mirrors

A novel method to characterize CMOS process fluctuations in subthreshold current mirrors （SCM） is reported. The proposed model is succinct in methodology and calculation complexity compared with previous statistical models. However,it provides favorable estimations of CMOS process fluctuations on the SCM circuit, which makes it promising for engineering applications. The model statistically abstracts physical parameters, which depend on the IC process, into random variables with certain mean values and standard deviations, while aggregating all the random impacts into a discrete martingale. The correctness of the proposed method is experimentally verified on an SCM circuit implemented in an SMIC 0.18μm CMOS 1P6M mixed signal process with a conversion factor of 100 in an input range from 100pA to lμA. The pro- posed theory successfully predicts - 10% of die-to-die fluctuation measured in the experiment, and also suggests the -lmV of threshold voltage standard deviation over a single die,which meets the process parameters suggested by the design kit from the foundry. The deviations between calculated probabilities and measured data are less than 8%. Meanwhile, pertinent suggestions concerning high fluctuation tolerance subthreshold analog circuit design are also made and discussed.

A Novel Ultra Low Power High Performance Atto-Ampere CMOS Current Mirror with Enhanced Bandwidth

A novel CMOS atto-ampere current mirror （AACM） is proposed which reaches the minimum yet reported current range of 0.4 aA. Operation of this circuit is based on the source voltage modulation instead of the conventionally used gate voltage modulation which interestingly prevents usage of commonly required voltage shifting in those circuits. The proposed circuit has a simple structure prohibiting large chip area consumption which consumes extremely low power of 1.5 μW. It is thus the best choice for ultra low power low voltage （ULPLV） applications. By using a very simple frequency compensation technique, its bandwidth is widened to 15.8 kHz. Simulation results in SMIC （Semiconductor Manufacturing International Corporation） 0.18 μm CMOS technology with Hspice are presented to demonstrate the validation of the proposed current mirror.

High-Performance CMOS Current Mirrors: Application to Linear Voltage-to-Current Converter Used for Two-Stage Operational Amplifier

This paper presents two schemes of high performance CMOS current mirror, one of them is used for operational tran-sconductance amplifier (OTA) in analog VLSI systems. The linearity, output impedance, bandwidth and accuracy are the most parameters to determine the performance of the current mirror. Here a comparison of two architectures based on same architecture of the amplifier is presented. This comparison includes: linearity, output impedance, bandwidth and accuracy. These two circuits are validated with simulation in technology AMS 0.35 μm. An operational amplifier based on the adapted current mirror is proposed. Its frequency analysis with large bandwidth is validated with the same technology.

Very Low Power,Low Voltage,High Accuracy,and High Performance Current Mirror

A novel low power and low voltage current mirror with a very low current copy error is presented and the principle of its operation is discussed. In this circuit, the gain boosting regulated cascode scheme is used to improve the output resistance, while using inverter as an amplifier. The simulation results with HSPICE in TSMC 0.18 μm CMOS technology are given, which verify the high performance of the proposed structure. Simulation results show an input resistance of 0.014 Ω and an output resistance of 3 GΩ. The current copy error is favorable as low as 0.002% together with an input （the minimum input voltage of Vin,min- 0.24 V） and an output （the minimum output voltage of Vout,min~ 0.16 V） compliances while working with the 1 V power supply and the 50 μA input current. The current copy error is near zero at the input current of 27 μA. It consumes only 76μW and introduces a very low output offset current of 50 pA.

Eddy current quantitative evaluation of high-speed railway contact wire cracks based on neural network

Purpose–The purpose of this study is to study the quantitative evaluation method of contact wire cracks by analyzing the changing law of eddy current signal characteristics under different cracks of contact wire of high-speed railway so as to provide a new way of thinking and method for the detection of contact wire injuries of high-speed railway.Design/methodology/approach–Based on the principle of eddy current detection and the specification parameters of high-speed railway contact wires in China,a finite element model for eddy current testing of contact wires was established to explore the variation patterns of crack signal characteristics in numerical simulation.A crack detection system based on eddy current detection was built,and eddy current detection voltage data was obtained for cracks of different depths and widths.By analyzing the variation law of eddy current signals,characteristic parameters were obtained and a quantitative evaluation model for crack width and depth was established based on the back propagation(BP)neural network.Findings–Numerical simulation and experimental detection of eddy current signal change rule is basically consistent,based on the law of the selected characteristics of the parameters in the BP neural network crack quantitative evaluation model also has a certain degree of effectiveness and reliability.BP neural network training results show that the classification accuracy for different widths and depths of the classification is 100 and 85.71%,respectively,and can be effectively realized on the high-speed railway contact line cracks of the quantitative evaluation classification.Originality/value–This study establishes a new type of high-speed railway contact wire crack detection and identification method,which provides a new technical means for high-speed railway contact wire injury detection.The study of eddy current characteristic law and quantitative evaluation model for different cracks in contact line has important academic value and practical significance,and it has certain guiding significance for the detection technology of contact line in high-speed railway.

NEW DARK CURRENT SUPPRESSION CMOS READOUT CIRCUIT WITH NOVEL CDS STRUCTURE FOR LARGE FORMAT QWIP FPA

A new Dark Current Suppression (DCS) CMOS readout circuits for large format Quantum-Well-Infrared Photo-detector (QWIP) Focal-Plane-Array (FPA) with novel Correlated-Double-Sampling (CDS) structure based on dynamic source-follower are proposed, which can overcome the drawbacks of the present techniques, such as sensitive to the non-uniformity of the QWIP materials, poor readout noise features, low frame frequency, limited injection efficiency and dynamic range, etc. The dummy is adopted to realize dark current suppression, while the cascode current mirror (with current ratio of 1:10) can increase charge sensitivity and reduce integration time. Through the novel CDS structure, the output waveform is boxcar, and the frame frequency is increased. Simulation results demonstrate that, in high background sense, the proposed DCS circuit can suppress the dark current, achieve good readout performance, such as low power consumption, high charge sensitivity, high resolution, large dynamic range, and insensitive to the non-uniformity of the QWIP materials.

Effect of Mirror Magnetic Field on Abnormal Glow Discharge of Four-Anode Device

Abstract In the four-anode device, the mirror magnetic field affects the characteristics of charged particles motion, so that the current-voltage relations of glow discharge are changed. Firstly, the discharge device is introduced, and the distribution of mirror magnetic field generated by the loops surrounding the discharge chamber is presented. Both the discharge current-voltage characteristics and the radial distributions of electron density are measured, respectively, with/without the magnetic field. When the discharge occurs in a 99.99% helium with a pressure ranging from 100 Pa to 800 Pa without magnetic field, the voltage, sustaining a certain abnormal glow discharge current, decreases with the increase in gas pressure. With a mirror magnetic field of certain intensity, the discharge voltage increases with the current in a rate slower than that without the magnetic field. Moreover, when the magnetic field intensity increases, the discharge voltage first decreases then increases. Simultaneously, the mirror magnetic field affects the moving characteristics of charged particles, and causes a more inhomogeneous electron density.

高精度电压电流转换电路中电流镜校准技术

电流镜输出误差主要由3个不同失配源造成:漏源电压(V_(DS)),阈值电压(V_(th)),跨导系数(β)。其中,第一项V_(DS)失配通常是由有限输出阻抗引起的确定性误差,该误差可以通过使用级联结构以及增益提升技术避免,后两项V_(th)和β失配是由工艺引起的随机性误差。为解决电流镜因工艺失配现象导致的电压电流(Voltage to Current)转换电路精度、线性度较差的问题,提出了一种动态元件匹配(Dynamic Element Match,DEM)以及修调技术(TRIM)相结合的电流镜校准方法,该方法使用TRIM技术将待校准输出电流镜支路和基准电流镜支路之间的误差电流,通过电容与MOS管转换成校准电流后反馈流入待校准输出电流镜支路完成校准,并通过DEM技术切换多条待校准输出电流镜支路完成校准的同时使输出误差平均化。本文采用SMIC 0.18μm BCD工艺对所提出的V-I转换电路进行了电路设计,仿真结果表明,V-I转换电路的输出电流的失配误差从0.12%下降到了0.03%,有效位数ENOB达到了11.2 bit,总谐波失真THD为−72.6 dB。

快速反射镜双线性插值标定技术

为满足光电系统中对快速反射镜高指向精度的需求,对基于电涡流传感器测量的快速反射镜二维角度标定技术进行研究。分析了利用电涡流传感器进行二维角度测量的工作原理,设计了快速反射镜角度标定系统。对多项式拟合、双线性插值两种标定模型进行了理论分析和实验测试。结果表明,在±1000″角度范围内,双线性插值法标定的误差在2″以内,比传统的多项式拟合法标定精度高。标定精度的提高对实现快速反射镜高精度指向具有十分重要意义。

tDCS联合MT对脑卒中患者上肢功能和日常生活活动能力康复效果的Meta分析

目的系统评价经颅直流电刺激(tDCS)联合镜像疗法(MT)对脑卒中患者上肢功能和日常生活活动能力的康复效果。方法计算机检索PubMed、Web of Science、The Cochrane library、Embase、中国知网、万方、维普和中国生物医学文献数据库,收集所有经tDCS联合MT治疗脑卒中患者上肢障碍的随机对照试验,检索时限从建库至2023年1月,由两名研究者独立提取数据。使用RevMan5.4软件进行Meta分析。评价主要结局指标:Fugl-Meyer上肢功能评定量表(FMA-UL)评分和改良Barthel指数量表(MBI)评分。次要结局指标:盒子积木测试(BBT)评分。结果共纳入7篇随机对照试验,包含379例患者。Meta分析结果显示,与单独tDCS组相比,联合组FMA-UL评分[MD=5.17,95%CI(3.80,6.54)]和MBI评分[MD=6.71,95%CI(4.61,8.80)]均显著提高;与单独MT组相比,联合组FMA-UL评分[MD=6.72,95%CI(3.67,9.76)]、MBI评分[MD=17.91,95%CI(2.49,33.33)]及BBT评分[MD=9.52,95%CI(3.30,15.74)]均显著提高。结论相较于单独使用tDCS或MT,tDCS联合MT改善脑卒中患者上肢运动功能和日常生活活动能力的疗效更显著。

Rail temperature rise characteristics caused by linear eddy current brake of high-speed train

The rail temperature rises when the linear eddy current brake of high-speed train is working, which may lead to a change of rail physical characteristics or an effect on train operations. Therefore, a study concerning the characteristics of rail temperature rise caused by eddy current has its practical necessity. In the research, the working principle of a linear eddy current brake is introduced and its FEA model is established. According to the generation mechanism of eddy current, the theoretical formula of the internal energy which is produced by the eddy current is deduced and the thermal load on the rail is obtained. ANSYS is used to simulate the rail temperature changes under different conditions of thermal loads. The research result shows the main factors which contribute to the rising of rail temperature are the train speed, brake gap and exciting current. The rail temperature rises non-linearly with the in- crease of train speed. The rail temperature rise curve is more sensitive to the exciting current than the air gap. Moreover, the difference stimulated by temperature rising between rails of 60 kg/m and 75 kg/m is presented as well.

深空探测中磁强计在轨标定研究进展

磁场测量是深空探测的重要任务之一,高精度的磁场测量对研究行星宜居性、空间等离子体环境等具有重要意义.磁通门磁强计是空间探测任务中最广泛使用的仪器之一.然而其磁补偿会随时间缓慢变化,因此,在卫星飞行期间需要定期对磁强计的磁补偿实施在轨标定.本文综述了基于空间物理现象对星载磁强计实施在轨标定的方法.根据计算磁补偿的方式,这些方法可分为两类.第一类方法通过公式计算磁补偿,如基于阿尔芬波动特征的Belcher方法、Hedgecock方法和Davis-Smith方法,以及一维和三维磁镜模方法;这类方法中,Davis-Smith方法被认为是计算磁补偿的最优方法.第二类方法通过概率获取磁补偿的最优解,该类方法被称为新一代在轨标定技术,目前已发展出六种算法;该技术可使用阿尔芬波动、磁镜结构和电流片中的一种或多种现象来实施在轨标定,另外,该技术也可以使用足够数据量(如4小时)的任意行星际磁场数据来计算磁补偿.与Davis-Smith方法相比,新一代在轨标定技术具有很好的兼容性(可同时使用不同的物理现象)和拓展性.除了太阳风,该技术还能在火星磁鞘中实施在轨标定.目前,该技术已为“天问一号”环绕器的磁场数据提供标定服务.

Interruption Characteristics of High-speed Switches in 500 kV Fault Current Limiter with High Coupled Split Reactance

A 500 kV high-voltage AC fault current limiter(FCL)based on a high coupled split reactor(HCSR)is pro-posed by the National key R&D project team.Low impedance under normal conditions and high impedance under short-circuit conditions are accomplished by the cooperation of HCSR and high-speed switches.High-speed switches play an important role in current limiting processes,thus interruption characteristics of the high-speed switch in the 500 kV FCL are studied in this paper.The simulation model of the FCL and the external equivalent power grid are established.The short-circuit current and recovery voltage characteristics of the high-speed switch in FCL are simulated.The results show that maximum DC component of the short-circuit current of the high-speed switch reaches 91%,the maximum peak value is 118 kA,and the longest arcing time is 14.8 ms.There is a discontinuity in the curve of the short-circuit current peak and arcing time as a function of the short-circuit occurrence time;the peak recovery voltage of a single break of the high-speed switch has a maximum value of 87.5 kV under a three-phase ungrounded short-circuit condition,and the rate of rise of recovery voltage is o.22 kV/s.The recovery voltage peak shows a period change with the short-circuit occurrence time,and the period is 10 ms.The effects of the shunt capacitor value and short-circuit ground resistance on the recovery voltage of high-speed switching are also studied.The research can be used for reference by R&D personnel and testersof500kVFCLs.Index Terms-Fault current limiter(FCL),high coupled split reactor(HCSR),high-speed switch,interruption characteristics,short circuit current.

一种片上高稳定性RC振荡器设计

基于片上系统对高稳定性时钟的需求,采用sk110 nm工艺设计了一款高稳定性RC振荡器。采用比较器失调电压消除结构、比较器延时测量电路以及斩波电流镜结构电路提高了RC振荡器的稳定性。使用Cadence Spectre工具进行仿真验证,结果表明在5 V电源电压、TT工艺角、27℃环境下,振荡器输出频率为119.4 kHz;在-40~125℃温度变化范围内,电源电压为5 V情况下,输出频率变化范围在±0.5%以内;在4.5~5.5 V电源电压变化范围内,温度为27℃情况下,输出频率变化范围在±0.25%以内,适合集成到片上系统中。

自适应光学波前校正器技术发展现状

波前校正器是自适应光学系统中的关键部件,相关技术已得到了多年的积累与发展。本文介绍了多种目前常用的波前校正器件,包括分离促动器连续表面变形镜、拼接子镜变形镜、薄膜变形镜、双压电片变形镜、微电子机械系统变形镜以及基于液晶技术的空间光调制器和自适应次镜等,给出了它们的实现方式及其基本工作原理,并从空间校正频率和校正速度等方面对各校正器的性能进行了比较。最后,总结了在新应用的需求下,波前校正器件的技术创新及发展趋势。

低杂散锁相环中的电荷泵设计

用TSMC0.18μm CMOS工艺设计并实现了一种电荷泵电路，传统的电荷泵电路中充放电电流有较大的电流失配,电流失配导致相位偏差,从而引起杂散并降低了锁相环的锁定范围，文中采用与电源无关的基准电流源电路,运用运算放大器和自偏置高摆幅共源共栅电流镜电路实现了充放电电流的高度匹配,从而降低了杂散。测试结果表明：电源电压1.8V时,电荷泵电流为0.475mA,在0.3-1.6V输出电压范围内电流失配小于10mA,功耗为6.8mW。