The effect of pulse voltage rise rate on the polypropylene surface hydrophilic modification by ns pulsed nitrogen DBD

The nanosecond(ns) pulsed nitrogen dielectric barrier discharge(DBD) is employed to enhance the hydrophilicity of polypropylene(PP) surface and improve its application effect.The discharge characteristics of the ns pulsed nitrogen DBD with different pulse rise times(from 50to 500 ns) are investigated by electrical and optical diagnostic methods and the discharge uniformity is quantitatively analyzed by image processing method.To characterize the surface hydrophilicity,the water contact angle(WCA) is measured,and the physical morphology and chemical composition of PP before and after modification are analyzed to explore the effect of plasma on PP surface.It is found that with increasing pulse rise time from 50 to 500 ns,DBD uniformity becomes worse,energy efficiency decreases from 20% to 10.8%,and electron density decrease from 6.6 × 10^(11)to 5.5 × 10^(11)cm^(-3).The tendency of electron temperature is characterized with the intensity ratio of N_(2)/N_(2)^(+)emission spectrum,which decreases from 17.4 to15.9 indicating the decreasing of T_(e) with increasing pulse rise time from 50 to 500 ns.The PP surface treated with 50 ns pulse rise time DBD has a lower WCA(~47°),while the WCA of PP treated with 100 to 500 ns pulse rise time DBD expands gradually(~50°–57°).According to the study of the fixed-point WCA values,the DBD-treated PP surface has superior uniformity under50 ns pulse rise time(3° variation) than under 300 ns pulse rise time(8° variation).After DBD treatment,the increased surface roughness from 2.0 to 9.8 nm and hydrophilic oxygencontaining groups on the surface,i.e.hydroxyl(-OH) and carbonyl(C=O) have played the significant role to improve the sample’s surface hydrophilicity.The short pulse voltage rise time enhances the reduced electric field strength(E/n) in the discharge space and improves the discharge uniformity,which makes relatively sufficient physical and chemical reactions have taken place on the PP surface,resulting in better treatment uniformity.

A model for predicting bubble rise velocity in a pulsed gas solid fluidized bed

Bed stability, and especially the bed density distribution, is affected by the behavior of bubbles in a gas solid fluidized bed. Bubble rise velocity in a pulsed gas-solid fluidized bed was studied using photographic and computational fluid dynamics methods. The variation in bubble rise velocity was investigated as a function of the periodic pulsed air flow. A predictive model of bubble rise velocity was derived: ub=ψ(Ut+Up-Umf)+kp(gdb)(1/2). The software of Origin was used to fit the empirical coefficients to give ψ = 0.4807 and kp = 0.1305. Experimental verification of the simulations shows that the regular change in bubble rise velocity is accurately described by the model. The correlation coefficient was 0.9905 for the simulations and 0.9706 for the experiments.

Design and Simulation of Solid State Pulser with Fast Rise Time and Double-exponential Waveform

Voltage pulses with fast rise time can be obtained from Marx circuits based on avalanche transistors. In this research, the ZETEX avalanche transistors are used as the switches in a Marx circuit to generate stable voltage pulses with double-exponential waveform and fast rise time. By using these transistors, the circuit is able to generate higher pulsed voltage with fewer stages. A three stages and a ten stages Marx circuit, as well as their triggering circuits, are designed. The two Marx circuits are also tested by simulations based on the Pspice code and by experiments, results of which are consistent with each other. With the ten stages Marx circuit, we obtain positive and negative pulses with the rise time of about 1.5 ns, the amplitude above 1 100 V, and the pulse width below 5 ns. It is proved that the proposed Marx circuit equipped with avalanche transistors could be an effective kind of solid-state pulse generator.

Pair Production in an Intense Laser Pulse: The Effect of Pulse Length

Production of positron-electron (e^(+) e^(-) ) pairs in an intense laser pulse is investigated by solving the Dirac equation with analytical and numerical methods.We observe that the probability of the pair production will firstly decrease slowly as the pulse length T becomes shortened.Then it will increase until T is reduced to the Compton time Tc =(h)/(mec) ≈ 1.29 × 10^(-21)s and finally decrease exponentially to zero.Hence,for a prominent pair production,we not only require that the electric field strength should be higher than the Schwinger critical value Ecr =m^(2)c^(3)/(e(h)) ≈ 1.32 × 10^(16) V/cm,but also that the pulse duration T should be larger than Tc.The latter is shown to be related to momentum requirement for the transition.For fields with different pulse lengths,the phase and chirp influences upon the pair production are also explored.

The Neutron-Gamma Pulse Shape Discrimination Method for Neutron Flux Detection in the ITER

The neutron flux monitor （NFM）, as a significant diagnostic system in the International Thermonuclear Experimental Reactor （ITER）, will play an important role in the readings of a series of key parameters in the fusion reaction process. As the core of the main electronic system of the NFM, the neutron-gamma pulse shape discrimination （n-γ PSD） can distinguish the neutron pulse from the gamma pulse and other disturbing pulses according to the thresholds of the rising time and the amplitude pre-installed on the board, the double timing point CFD method is used to get the rising time of the pulse. The n-γ PSD can provide an accurate neutron count.

Demagnetization Research on PMs in the Halbach Magnetized Pulsed Alternator

Demagnetization behavior of Halbach magnetized compensated pulsed alternator(CPA)is studied by using finite element method(FEM)under the different demagnetization factors in this paper.The effect of armature reaction magnetic field and thermal rise on demagnetization of PMs is analyzed.This paper investigates the effect of different demagnetization factors on magnetic field distribution,load current,and no-load phase voltage.A series of dynamic demagnetization points in Halbach array permanent magnet(PM)are evaluated to search the worst working point.Partial demagnetization risk can be represented by the worst working point,and the global demagnetization of the PM is represented by the no-load phase voltage characteristics after discharge.The research results demonstrated that the compensation shield with a certain thickness can increase the discharge current and weaken the demagnetization influence of armature reaction.The demagnetization effect of armature reaction on PMs at high temperatures will be strengthened.

Effect and mechanism of on-chip electrostatic discharge protection circuit under fast rising time electromagnetic pulse

The electrostatic discharge(ESD)protection circuit widely exists in the input and output ports of CMOS digital circuits,and fast rising time electromagnetic pulse(FREMP)coupled into the device not only interacts with the CMOS circuit,but also acts on the protection circuit.This paper establishes a model of on-chip CMOS electrostatic discharge protection circuit and selects square pulse as the FREMP signals.Based on multiple physical parameter models,it depicts the distribution of the lattice temperature,current density,and electric field intensity inside the device.At the same time,this paper explores the changes of the internal devices in the circuit under the injection of fast rising time electromagnetic pulse and describes the relationship between the damage amplitude threshold and the pulse width.The results show that the ESD protection circuit has potential damage risk,and the injection of FREMP leads to irreversible heat loss inside the circuit.In addition,pulse signals with different attributes will change the damage threshold of the circuit.These results provide an important reference for further evaluation of the influence of electromagnetic environment on the chip,which is helpful to carry out the reliability enhancement research of ESD protection circuit.

纳秒激光脉冲宽度对2024铝合金损伤特性的影响

飞机激光除漆对2024铝合金蒙皮可能造成潜在的损伤,需探究激光参数变化对基体材料表面的作用规律,其中脉冲宽度对激光-材料作用与材料损伤特性具有重要影响。本文采用COMSOL Multiphysics软件模拟分析了不同脉冲宽度时激光作用铝合金表面的温升特性,并借鉴ISO 11254 1-on-1激光损伤阈值测试方法研究了脉冲宽度对铝合金损伤阈值的影响,进一步分析了不同脉冲宽度下的烧蚀凹坑微观形貌、直径与深度变化规律。结果表明:铝合金表面峰值温度随脉冲宽度增加而降低;脉冲宽度从150 ns增加到240和330 ns时,铝合金损伤阈值从9.96 J/cm^(2)分别增加到11.24和12.66 J/cm^(2),当激光能量密度达到损伤阈值时,3μm厚氧化膜被完全损伤,破坏了铝合金表面完整性;烧蚀凹坑直径和深度随脉冲宽度增加而增加,深度受影响程度更大。该研究可为激光与材料作用的脉冲宽度选择提供一定的参考。

水介质预击穿过程液相温度纹影诊断技术研究

为研究水中亚毫秒脉冲放电过程液相温度的变化,构建了适用于水中脉冲放电的纹影观测系统,提出了水中脉冲放电过程温度诊断系统的影响因素及标定方法,获得了水中脉冲放电过程温度场的径向分布。与有限元仿真对比分析表明,当径向距离小于0.9 mm时,纹影诊断温度相对于仿真结果的偏差小于8%,为水中脉冲放电机理研究提供了技术基础。

脉冲触发对固体火箭发动机内弹道压强抬升的影响

为了解固体火箭发动机在脉冲触发激励下的工作性能,设计了一种脉冲触发实验系统并开展实验研究,建立了脉冲触发内弹道模型。结果表明,实验系统压强抬升响应时间在25 ms以内,相较于延长段位置,发动机头部的压强扰动更大,扰动传播速度为1259 m/s;脉冲触发器峰值压强与发动机压强抬升预示误差均小于6%;延长段越长,脉冲触发产生的压强抬升越小;脉冲药量越大,压强抬升越大,脉冲药量与压强抬升呈近线性关系,药量从3 g增加到8 g,发动机压强抬升率从8.142%提升到31.594%;发动机压强抬升随脉冲触发器节流孔径的提升显著增大,孔径从1 mm增大到4 mm,压强抬升率从1.656%提升到了27.448%,壅塞作用导致1 mm的节流孔径无法达到脉冲触发效果;发动机压强抬升随着发动机喉径的增大而减小,喉径从12.50 mm提升到14.00 mm,压强抬升率从19.204%降低到了14.771%;对于本实验系统,触发时刻对发动机压强抬升影响小。

355 nm激光应用于血栓及其钙化组织消融的实验研究

相较于308 nm准分子激光器,355 nm脉冲固体激光器在峰值功率、成本和方便性等方面更具优势,使用离体新鲜猪血凝块与新鲜鸡胫骨块作为类血栓及其钙化组织,研究355 nm脉冲固体激光的组织消融特性及规律。实验结果显示:组织消融孔洞形貌良好,无颗粒沉积;消融后微粒直径均在10微米量级,处于人体可自然代谢的范围,且25 mJ~200 mJ范围内脉冲能量越小,消融后微粒越小;灌注条件下,热影响区组织温升小于4.5℃,不会对血管壁造成热损伤。故355 nm脉冲固体激光可有效消融血栓及其钙化组织,具有较好应用前景。

基于脉冲变压器的快前沿固态触发器

结合理论求解、仿真分析与实验验证,确定了影响脉冲变压器型触发器输出前沿的主要因素,并研制了一台能可靠触发真空沿面闪络开关导通的快前沿固态触发器。研究结果表明:影响触发器输出脉冲前沿的关键因素为脉冲变压器漏感、匝数比和半导体开关开通速度;不同绕制方式的脉冲变压器漏感差异很大,最小漏感绕法的变压器漏感值低1个数量级;选用开通速度优于15 ns的碳化硅金属氧化物半导体场效应晶体管(SiC MOSFET)、绕制低漏感(小于0.5μH)的脉冲变压器,实现了前沿为20.4 ns(10%~90%)、幅值为16.5 kV的快前沿输出;控制SiC MOSFET的驱动脉宽在35~55 ns变化可以控制触发电流峰值在35~55 A范围内变化。

具有快前沿的固态Marx电源的研究

纳秒脉冲电场消融要求在100Ω负载上产生数千伏的纳秒脉冲,加快脉冲前沿有利于获得更窄的纳秒脉冲。提出了一种具有快速前沿的固态Marx发生器,在每级电路中插入一个电感,并且让放电管和充电管同时导通数十纳秒,等放电管完全开通后,关断充电管,对负载进行放电,以消除放电管和放电回路杂散电感对脉冲前沿的限制,获得具有快前沿的高压脉冲。搭建了32级Marx样机,实验中通过调节直通时间,在100Ω的低阻负载上获得了电压上升沿35 ns、脉宽800 ns、电流186 A的高压脉冲。对比并分析了充电管和放电管直通时间对上升沿的影响,发现直通时间越长,脉冲电流的前沿越快。输出端的峰值电流最大可达186 A。表明该脉冲电压源可以有效地提高电流的输出,提高系统带载能力。该方案相比于传统的改进方法,提高了系统抗干扰能力的同时,也减少了所使用开关管的数量,降低了脉冲电源的成本。

电磁脉冲阀差动气道与喷吹性能的研究

电磁脉冲阀是脉冲喷吹袋式除尘器清灰系统的主要装置,其性能优劣直接决定了滤袋的清灰效果,并影响滤袋使用寿命和设备运行阻力。通过电磁脉冲阀理论分析和实验室对比试验,研究新型差动气道与喷吹性能,提出“短促脉冲”的清灰技术,从而达到低碳和节能的效果。

基于铁氧体传输线的百纳秒脉冲前沿陡化技术研究

基于铁氧体传输线脉冲陡化原理,利用COMSOL软件建立了铁氧体传输线的电磁场仿真模型,研究了脉冲陡化的影响因素及特征规律,根据仿真模型设计了2种不同直径磁芯的铁氧体传输线,并建立了实验测试平台,对传输线陡化后的脉冲前沿进行测试。仿真及实验结果均表明,铁氧体传输线陡化后的脉冲前沿随输入电压幅值、传输线长度的增加而减小,随磁芯直径的减小而减小,实验结果与仿真结果规律一致。磁芯直径为40 mm,线长为1500 mm的铁氧体传输线可将幅值为120 kV的脉冲电压的前沿由124 ns陡化至14.4 ns,整个脉冲源的抖动为1.83 ns,验证了铁氧体传输线替代FLTD触发器中气体陡化开关的可行性。

基于CDEGS的脉冲功率装置接地优化设计

为降低脉冲功率装置接地点地电位升(grounding potential rise,GPR),使用PSpice进行了Marx型脉冲功率装置初步电路模拟,使用CDEGS进行了接地网频域仿真,结合施工难度及效费比,对接地网进行优化。研究了水平地网密度、地网形状、垂直接地极长度、引下线参数对GPR的影响。结果表明,水平地网密度对工频接地电阻影响较小,对高频散流性能影响较大;实验室地面混凝土钢筋可有效降低地面跨步电压;电流注入点采用放射线接地方法可有效提高地网高频散流性能;高频情况下,近距离铺设的垂直接地极屏蔽效应明显;引下线电感是影响接地点GPR的最大因素。优化后地网参数包括埋深为0.4 m,引下线截面半径为0.25 m,16条放射线,垂直接地极长度为7 m,地网间距为1 m。当激励电流为11 MHz,2.6 kA时,注入点GPR较未优化时降低66.3%,降阻效果明显。

射频前端快上升沿电磁脉冲防护电路仿真分析

针对强电磁脉冲极易通过射频前端进入电子设备内部对敏感电子器件造成伤害的问题,设计了一款工作于C波段的射频前端快上升沿电磁脉冲防护电路。电路采用PIN二极管级联的方式构建四级防护电路,同时引入高通滤波器抑制工作频段以下信号,防止其对设备造成干扰。仿真结果表明,通过控制PIN二极管的偏置电压和电流,可实现对电磁脉冲的快速响应;经过逐级削减输入功率,可有效降低尖峰泄漏;在工作频段内,防护电路可将4 kV的快沿方波脉冲限制在2 V以下,其响应时间小于1 ns,插入损耗小于0.146 dB,驻波比小于1.413,回波损耗小于-15.329 dB,且可有效降低尖峰泄漏,对工作在C波段的卫星电视地面通信设备抵御强电磁脉冲的侵扰具有较好的效果。

平行磁场对脉冲针–板介质阻挡放电物理化学特性的影响

为在大气压下产生高强度的介质阻挡放电(dielectric barrier discharge,DBD)等离子体,该文利用永磁铁产生平行于电场方向的磁场,用于增强纳秒脉冲针–板DBD等离子体的物理化学活性,并探究不同脉冲参数下磁场对等离子体特性的影响规律和机制。考察平行磁场辅助脉冲针–板DBD等离子体的动态演化特性,并从电学、光学和臭氧生成特性等方面研究了脉冲电压幅值、上升沿时间和下降沿时间等参数对平行磁场辅助脉冲针–板DBD特性的影响规律。实验结果表明:平行磁场通过磁化电子改变DBD等离子体特性;施加平行磁场后,针–板DBD中空间流光放电及介质表面流光放电强度增强;不同脉冲放电参数下,施加平行磁场对放电强度及臭氧产量均显示出增强效果,在短脉冲上升沿时间条件下平行磁场的增强效果尤为显著。

基于激光热成像的铝合金表面裂纹宽度定量检测

针对激光热成像技术定量检测铝合金表面微小裂纹宽度精度不足的问题,通过系统分析表面裂纹处热传导规律,并构建长脉冲激光激励条件下铝合金表面裂纹位置处准稳态温度场的温度分布模型,发现沿激光线方向的温度分布能够定量表征裂纹宽度。搭建了激光红外热成像试验平台并进行试验,获得了准稳态温度场下的温升分布规律,分析了不同宽度裂纹的温升分布特征和温升变化特征,基于温升分布特征参量和温升变化特征参量,采用比值定义法构建了不依赖激光功率的裂纹宽度综合指标。结果表明,所构建的空域特征参量综合指标显著提高了裂纹宽度检测的可靠性和准确性,能够实现50~700μm宽度裂纹的定量检测,该结果能够为实现激光红外热成像技术在航空航天裂纹量化检测的应用奠定坚实基础。

近断层脉冲型地震动强度指标与高耸结构损伤关联性

为了研究近断层脉冲型地震动作用下适用于评价高耸结构抗震性能的地震动强度参数,基于加速度反应谱提出一种同时考虑结构周期延长和高阶振型效应的地震动强度指标。分别以120 m和240 m的钢筋混凝土烟囱结构为研究对象,使用OpenSEES程序,在近断层脉冲型地震动作用下,揭示了高耸混凝土结构的损伤指标(Park-Ang损伤指标、最大层间位移角、最大曲率、最大楼层加速度以及最大顶点位移)与37个地震动强度指标的关联性。研究结果表明:提出的地震动强度指标最适合用于预测高耸混凝土结构在近断层脉冲型地震作用下发生的Park-Ang损伤;与速度相关的地震动强度指标表现出与高耸结构损伤指标的较高的相关性;随着结构周期的增大,位移型的地震动强度指标与损伤的关联性有增长的趋势;此外,地面峰值加速度在表征高耸结构变形破坏方面存在局限性,但是可以用来分析非结构构件的抗震性能。研究结论可为选择合适的地震动强度指标和损伤指标评价高耸混凝土结构在近断层脉冲型地震动作用下的抗震性能提供参考。