水下等离子体声源放电特性和声特性实测与分析

在小型消声水池中,同步测量水下等离子体脉冲声源的放电特性和声特性,实验分析研究了其在单电极和多电极下负载注入峰值功率和放电能量对声特性的影响。结果表明,在相同的电极数和间距下,直达波脉冲声源级仅与负载注入峰值功率有关,气泡脉冲声源级和气泡周期则主要受放电能量影响,多电极放电通过减小单根电极放的电能量来减小气泡脉冲声源级和气泡周期。此外,在相同的充电电压下,减小充电电容对电极数的比,可以增大直达波脉冲声源级并压制气泡脉冲;负载注入峰值功率对放电能量的比对声特性的影响也呈现出类似规律。实测及其分析结果可为进一步优化水下等离子体脉冲声源的声特性提供参考。     

Analysis and research on acoustic efficiency of underwater plasma sound source

为研究水下等离子体声源放电系统的声效率问题,系统地分析了水下等离子体电晕放电和电弧放电两种放电方式的微观机理以及等离子体声源放电系统各部分之间的能量转换流程,建立了一套完整的系统声效率计算模型,同时设计了水下等离子体脉冲放电试验系统.通过比较和分析水下脉冲电晕放电和水下脉冲电弧放电的声效率发现,系统中电弧放电的声效率明显高于电晕放电.通过水下高压脉冲放电试验,详细分析了水下等离子体放电系统中关键部件对系统声效率的影响.分析结果表明:关键部件的设计和参数的优化配置对整个系统的声效率有重要影响;通过声效率的分析,能够准确评估水下等离子体声源的设计合理性.     

不同激励参数对DBD等离子体放电功率的影响

为探索DBD等离子体放电功率与各激励参数之间的联系,本文建立了二维的板-板电极简化仿真模型,分别研究了脉冲、正弦交流两种激励的放电频率、电压与放电功率间的具体函数关系。仿真结果显示:一定条件下,放电功率正比于脉冲电压峰值的1.381次方、正比于脉冲放电频率的1.097次方,即放电功率与脉冲电压峰值及脉冲放电频率间均有幂函数关系;放电功率与正弦交流电压幅值呈现指数函数关系,放电功率与正弦交流放电频率间近似线性关系;实际工程中,需要增大DBD等离子体放电功率时,应尽量选用提高电压峰值(幅值),而避免选择提高放电频率。     

棒尖端外形对低气压下棒-板短间隙放电特性影响研究

为研究棒尖端外形对低气压下棒-板短间隙放电特性的影响,利用低气压放电试验平台针对锥尖头、球头、平头三种棒电极在2~20 kPa气压范围内200~400 mm短间隙进行工频放电试验研究,并对棒尖端外形对击穿电压、电晕和等离子体通道外形的影响进行分析。研究结果表明:棒尖端外形对低气压下棒-板短间隙放电特性影响显著。在2~20 kPa气压范围内随气压升高,相同间隙距离不同棒尖端下的击穿电压幅值差逐渐增大;锥尖头和平头棒尖端电晕层存在电离集中点;球头和平头棒相对锥尖头棒-板间隙等离子体通道而言较粗且偏移角较大,等离子体通道末端与板电极存在较多接触点并呈现"多分支"状。研究成果对低气压下放电试验电极布置具有参考意义。     

储能电容充电电压对激波特性的影响分析北大核心CSCD

利用“液电效应”产生的等离子体冲激声源在岩石破碎、地质导向、确定位置等方向有巨大的应用价值,目前关于等离子体放电回路中充电电压与放电特性、冲激波特性的关联性仍缺乏进一步深入了解。基于水下等离子体放电实验平台,建立水下等离子体冲激声源的仿真模型,对比分析冲激声源放电典型的电压、电流及冲激波波形的实测和仿真结果,通过仿真模型研究不同充电电压下的放电特性与冲激波特性。结果表明,当充电电压从15 kV提高到25 kV时,冲激波强度峰值增大了31.9%,冲激波能量增大了53.8%,因外电路能量增加速率大于冲激波能量增加速率促使其转化效率降低了28.4%。通过改变充电电压来预测冲激波特性,对比分析不同充电电压下的冲激波强度、能量损耗及能量转化效率等,为水下冲激声源不同工程应用选取最佳的充电电压提供参考依据,也可根据充电电压对冲激波特性影响来设计水下等离子体冲激声源的充电储能部分。     

真空环境下指数脉冲放电等离子体特性分析

真空环境内金属电极放电产生的等离子体不同于气体放电等离子体,具有特殊的性质.本实验采用持续时间为10μs,幅值约600A的指数变化的脉冲电源进行放电;运用朗缪尔探针法对放电生成的等离子体的相关参数进行测量,讨论了放电生成的等离子体的特性,分析了电极间距对放电等离子体密度的影响;同时运用AnsoftMaxwell3D仿真软件对电极间的电场分布情况进行了仿真分析.实验发现采用指数脉冲放电能生成高密度的等离子体,且生成的等离子体密度随电极间距增大而增大.     

脉冲电弧放电电离甲醇/氨水溶液合成结晶氮化碳薄膜

利用脉冲电弧放电在大气压下产生的高密度等离子体研究了结晶氮化碳薄膜的低温合成。直流脉冲电弧等离子体由甲醇／氨水溶液液滴通过高压电极时诱导放电产生。利用扫描电子显微镜、X射线衍射、Raman光谱分析了薄膜样品的形貌和结构。在基片温度为450℃时所制样品的X射线衍射分析表明薄膜中含有α-C3N4和β-C3N4两种结构晶体，Raman光谱给出了明显的特征峰，这些特征峰与氮化碳晶体的理论预言值符合较好。当基片温度提高到550℃时．Raman光谱分析表明，样品为炭膜。     

SiH4射频放电功率耗散机制的光发射研究

采用ＯＭＡ－４０００测量了ＳｉＨ４射频辉光放电等离子体的光发射谱,研究了其谱线强度随放电射频功率和反应气体流量间的变化关系。发现在放电射频功率增加和反应气体流量升高的过程中,其等离子体状态分析发生性质不同的转变,这种转变联系到射叔功率耗散机制的变化。当反应气体流量增加时,电子获得能量的机制由阴极暗区加速转变为等离子体内电场的加热效应,而在放电功能升高的过程中,离子轰击阴极产生二次电子发射效应导致了     

100Pa下800mm棒-板间隙放电等离子体外部特征研究

为研究低气压下长间隙放电等离子体通道外部特征,利用试验平台对100 Pa下800 mm棒-板间隙交、直流放电进行观测,并对放电通道发展过程及其外部特征进行研究。研究结果表明:50 Hz交流和正极性直流电压下等离子体通道发展过程及通道外形差异显著,交流电压下等离子体通道自棒、板电极双向发展并双向消散,击穿后通道呈纺锤形且存在明暗条纹;正极性直流电压下等离子体通道自棒电极向板电极单向发展并向棒电极单向消散,击穿后通道呈亮度均匀的圆柱形。研究结果为低气压下长间隙放电特性研究提供参考。     

射频容性耦合等离子体阻抗影响因素研究

为了进一步探索射频容性耦合放电等离子体,本文建立了以容性耦合等离子体(CCP)为基础的板-板电极一维轴线简化仿真模型。仿真采用氦气为工作气体,使用约化电子传递属性并忽略重粒子对流,利用有限元算法,综合讨论了一定范围内放电参数(气体压强、输入功率、电极直径以及间隙长度)变化时,放电等离子体阻抗的变动情况,并根据仿真所得数据进行理论分析。结果表明:四种仿真条件下的等离子体均呈现容抗特性;当气压升高、放电间隙长度变大时,初期均有利于碰撞电离的发生,而后将成为限制因素,使得等离子体阻抗呈现先减小后升高的变化趋势;当电极直径增大、输入功率增加时,初期等离子体阻抗均呈下降趋势,但后续变化趋于平稳。     

Variation of the beam parameters of runaway electrons in a gas discharge under the conditions of nonuniform preliminary ionization

Within the theoretical model of a high-pressure hybrid nanosecond discharge with runaway electrons, a strong dependence of the electron beam amplitude, duration, and energy spectrum on the conditions of the preliminary ionization of a gas in the discharge gap is demonstrated. The conditions with uniform and nonuniform distributions of initial electrons in a coaxial diode filled with sulfur hexafluoride at atmospheric pressure are simulated. It is shown that the amplitude and current pulse profile of the electron beam substantially change upon the variation of the initial distribution of the electrons in the discharge gap.     

Analytical Solutions of the Frequency Shifts of Several Modes in Dynamic Force Microscopy Subjected to AC Electrostatic Force

Kelvin probe force microscopy is currently used to measure contact potential difference and topography of sample on a nanometer scale, based on the behaviors of the first two resonant frequencies. In this study, an analytical method to determine the frequency shifts of several modes in dynamic force microscopy subjected to AC electrostatic force is proposed. The numerical results determined by the proposed method are close to the experimental ones. If the amplitude and the frequency of the AC voltage are suitable, a large frequency shift and a linear relation between the frequency shift and the tip-sample distance will be obtained. In other words, properly controlling the AC voltage will increase the accuracy of measuring the sample's topography. Moreover, it is found that even without an optimized compensation dc voltage, increasing the first frequency shift and decreasing the tip radius and the half open angle of the tip can increase the accuracy of measuring a step height. Finally, it is found that when the oscillation amplitude and the tip-sample distance are constant, increasing the negative dc voltage will increase the accuracy of the measurement of contact potential by using the frequency shift. In addition, an assessment of the conventional perturbation method is presented and the two methods are compared.     

地震作用下桥梁结构横向碰撞模型及参数分析

针对桥梁结构在地震作用下梁体与横向挡块间的碰撞现象,采用非线性时程积分法,研究了横向地震作用下梁体与挡块间的碰撞效应。通过对刚体碰撞模型分析,推导出阻尼常数与恢复系数间的关系表达式,在此基础上建立了能考虑碰撞过程中能量损失的桥梁横向碰撞模型,并对碰撞刚度、初始间隙、恢复系数以及桥梁跨径等参数进行了影响分析。分析结果表明:最大撞击力随碰撞刚度和桥梁跨径的增大而增大,但随初始间隙的变化规律不明显;恢复系数对碰撞效应影响很大,忽略碰撞过程中的能量损失会高估碰撞反应。为减轻梁体与横向挡块间的碰撞效应,提出了挡块刚度的合理取值。     

高强钢丝断裂声发射试验研究

通过对单根高强钢丝和拉索的张拉破坏试验,获得了单根钢丝中裂纹扩展、钢丝破断及索中断丝点附近和远离声源处的声发射全波形。比较不同声源的波形、频谱及时频特征,结果可以看到,钢丝破断的全波形能量及持续时间都要远高于裂纹扩展信号,但其幅值与裂纹扩展的最大幅值相当;钢丝破断声源频谱峰值突出,基本都在43KHz,在全波形持续时间范围内,绝大部分能量都分布在一条43KHz的等频率时间带上;裂纹扩展波形包含几个频带,最大峰值出现在50-60KHz,高频部分出现在波形初至段,随时间增长,高频部分快速消失;断丝声源在索中传播一段距离后,能量会出现衰减,低频部分所包含的能量相对增多。     

Short-wavelength XeBr-Br gas discharge lamp

The output characteristics of a small-size gas-discharge lamp emitting in the 160–300 nm wavelength range are reported. The working medium—a mixture of xenon and bromine vapor—was excited in a longitudinal glow discharge in a quartz tube with an interelectrode distance of 100 mm. The emission spectrum is formed by the molecular lines of xenon bromide at 282 nm [XeBr(B-X)] and 220 nm [XeBr(D-X)] and the atomic resonance lines of bromine at 163.3 and 157.6 nm. An increase in the partial pressure of xenon in the working mixture from 130 to 800 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and an increase in the intensity of emission from xenon bromide molecules. The operation regime was optimized with respect to the energy supplied to the glow discharge and the working gas mixture pressure and composition. The optimum partial pressure of xenon is within 600–800 Pa, and that of bromine vapor, within 50–100 Pa. The average total VUV-UV output radiation power reached 7 W.     

基于目标能量特性的被动声引信

介绍了一种基于目标能量特性的被动声引信.通过分析目标经过声引信时的能量变化信息,得到一种寻求最佳起爆时刻的方法.试验结果表明,利用接收声源级的差值判断目标是否最近距离通过,从而决定是否输出起爆信号,这种方法可以寻求到最佳起爆时刻,为被动声引信的应用提供了重要的依据.     

Pulse distortion in transitions recorded with thin film pole tips

The transitions recorded on particulate, longitudinal media by a thin film ring head can exhibit a distortion at high write currents that adds an oscillatory structure to the density response and also degrades the amplitude at high density. The main data transition is recorded at the trailing edge of the gap, while the distortion is a second pulse written at the edges of the data track by the trailing edge of the trailing pole tip and at the expense of the transition recorded by the gap. This produces two pulses of opposite polarity with a constant peak-to-peak amplitude, separated by a distance equal to the thickness of the trailing pole tip and with the distortion appearing as a spurious pulse ahead of the data pulse.     

强振动下比例电磁铁输出力特性研究

为研究强振动对比例电磁铁输出力特性的影响,应用电磁场理论和强迫振动理论建立了强振动环境下比例电磁铁的动态数学模型和仿真模型,仿真分析了不同振动参数下比例电磁铁的气隙磁阻、动生感应电动势及输出力的变化规律,讨论了强振动对电磁铁输出力的影响原理。同时分析了衔铁质量、阻尼系数、弹簧刚度对比例电磁铁输出力波动的影响规律。结果表明:强振动幅值和频率与电磁铁的动生感应电动势的波动幅值正相关;比例电磁铁的气隙磁阻和输出力的波动幅值与强振动幅值呈线性正相关;随阻尼系数的增加,比例电磁铁输出力的波动幅值近似线性减小;弹簧刚度小于20 000N/m时比例电磁铁的输出力波动幅值随刚度增加而快速减小。研究结果为提高振动环境下比例元件的工作性能提供了理论参考。     

基于矢量水听器的南海海洋背景噪声测试

矢量声压振速联合处理建立在信号的声压和振速相位基础上,海洋环境边界影响将改变矢量声场声压振速的幅度和相位特性．首先根据南海环境条件结合水下目标辐射噪声测量,采用声场矢量简正波理论估算海面非相干偶极子噪声和水下点声源矢量强度随深度的变化,然后设计了可用于深海海域噪声测量的矢量水听器测试系统,获取了南海海域典型深度上的背景噪声矢量强度并进行了特性分析．结果表明：深海背景噪声谱级在500Hz以下基本上不随深度变化,在500Hz～3kHz频段浅深度背景噪声谱级略高于较深深度的背景噪声;振速垂直分量的背景噪声要小于声压和振速水平分量的噪声谱级．     

Investigation of low-temperature plasma generator with divergent channel of the output electrode and some applications of this generator

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-voltage characteristic) in a divergent channel and in a cylindrical channel of uniform cross section. The effect of divergent channel of the output electrode and of its expansion ratio on the pattern of physical processes in LTPGs of different designs is studied. Investigations are performed of the distribution of electric current and heat flux density along a channel with a segmented output electrode. The voltaic equivalents of heat fluxes to cathode and anode are determined. The process of “shunting” of discharge is investigated, which causes fluctuations of electric arc-burning voltage. The investigations involving an LTPG with divergent channel reveal that the voltage amplitude in the case of shunting decreases with increasing current strength and, at high currents of argon arc, does not exceed 1–2 V. Results are given of spectral and visual investigations of LTPG. It is demonstrated that, in an LTPG with divergent channel, the plasma temperature in the region of energy input at currents of 300 A and higher exceeds 30 000 K. The significant part is found which is played by vacuum ultraviolet radiation in the process of closing the arc to anode. The mechanisms of erosion of the tungsten cathode tip are investigated, which play an important part in increasing the cathode service life by way of recirculation of tungsten atoms because of their ionization in the discharge gap. Results are given of using an LTPG with divergent channel of the output electrode in plasma technologies of surface hardening, cutting, and hard-facing of metals. The technology of plasma hardening of wheel pairs, adopted by the RZhD (Russian Railroads) Joint-Stock Company, provides for increasing the service life of railroad wheels by a factor of 1.5–2.