Nonlinear behaviors in a pulsed dielectric barrier discharge at atmospheric pressure

In this paper, the temporal nonlinear behaviors of pulsed dielectric barrier discharge in atmospheric helium are studied numerically by a one-dimensional fluid model. The results show that the common single-period pulsed discharge with two current pulses per single voltage pulse can take place over a broad parameter range. The rising and falling times of the voltage pulse can affect the discharge characteristics greatly. When the discharge is ignited by a pulse voltage with long rising and falling times, a single-period pulsed discharge with multiple current peaks can be observed. Under appropriate rising and falling times of the voltage pulse, a stable period-two discharge can occur over wide frequency and voltage ranges. Also this period-two discharge can exhibit different current and voltage characteristics with changing the duty cycle. With other parameters fixed, the pulsed DBD could be driven to chaos through period-doubling route by increasing either the falling time or the frequency of voltage pulse.     

不同面积Kapton材料的放电特性实验研究

航天器表面介质材料在空间等离子环境下会产生放电现象,放电诱发的瞬态脉冲会对航天器在轨安全运行产生严重影响。通过对不同面积的125μm厚Kapton温控材料进行放电实验,对放电诱发的瞬态脉冲进行测量,总结分析其规律,得出4～36 cm2Kapton材料和64～225 cm2Kapton材料的放电波形存在比较大的差异,而且随着材料面积增加,Kapton材料的放电电流峰值、放电持续时间、放电电荷损失量和放电频率都相应的升高。对Kapton材料放电特性的研究,将为航天器带电防护设计和放电危害评估提供数据支持。     

内径20mm导向套筒内壁处理(1):空心阴极氩气放电特性研究

针对高端阀门内径20mm导向套内壁处理,采用高频高压脉冲电源,研究了氩气气氛下工作气压、脉冲电压和频率等参数对导向套空心阴极放电伏安特性的影响,并对工件间距及与阳极距离等放电结构进行了研究。结果表明:管内空心阴极放电需要一个稳定过程,脉冲电流随着时间的增加逐步降低,而后达到稳定放电阶段。提高脉冲电压或工作气压,管内空心阴极脉冲峰值电流增加。脉宽或频率的增加,脉冲峰值电流不变,但平均电流增加,且频率的增加使得激励时间减少。放电结构的分析表明,管间距的减少,放电电流变化不大,而管口与阳极之间距离的减少,使得放电峰值电流略有增加。以上研究结果为高端阀门小直径导向套等内壁薄膜制备提供了有效指导。     

梳状电极结构对大气压表面放电的影响

研究了梳状电极结构对大气压表面放电的影响,发现频率固定时放电电流随着外加电压的增加而增加,而电压固定时在某个频率范围内放电电流有最大值;在相同的电压和频率下较宽的电极条宽可以产生较大的放电电流,而电极条间距对放电电流几乎没有影响;用整块金属板做接地电极相比于梳状接地电极可以产生较大的放电电流;另外,较厚的高压电极可以在介质板表面产生更明亮、厚度更大的放电等离子体.     

Experimental study of atmospheric pressure surface discharge in helium

The surface discharge generated at atmospheric pressure in helium was examined by monitoring the current and voltage at the discharge electrode. The discharge generated in helium behaves differently when compared to that generated in other gases (e.g. air). The single discharge duration and the time between consecutive discharges are longer because there is a different mechanism of discharge evolution. The metastable helium atoms play the most important role for discharge generation. Streamer-like and glow types of discharge were observed. The decay of helium metastables concentration determines the discharge regime. Hence, operation conditions have strong influence on the discharge regime. The introduction of gas flow removes metastable quenchers (gaseous products from dielectric and electrode surfaces) and transition to glow discharge is observed. Also covering the discharge electrode with thin dielectric foil to suppress Auger de-excitation of metastables at metal surface leads to generation of atmospheric pressure glow surface discharge. Properties of this discharge are comparable with properties of glow discharge at low pressure (e.g. the electron concentration).     

Experimental study of atmospheric pressure surface discharge in helium

The surface discharge generated at atmospheric pressure in helium was examined by monitoring the current and voltage atthe discharge electrode. The discharge generated in helium behaves differently when compared to that generated in other gases (e.g. air). The single discharge duration and the time between consecutive discharges are longer because there is a different mechanism of discharge evolution. The metastable helium atoms play the most important role for discharge generation. Streamer-like and glow types of discharge were observed. The decay of helium metastables concentration determines the discharge regime. Hence, operation conditions have strong influence on the discharge regime. The introduction of gas flow removes metastable quenchers /gaseous products from dielectric and electrode surfaces) and transition to glow discharge is observed. Also covering the discharge electrode with thin dielectric foil to suppress Auger de-excitation of metastables at metal surface leads to generation of atmospheric pressure glow surface discharge. Properties of this discharge are comparable with properties of glow discharge at low pressure (e.g. the electron concentration).     

脉冲放电工艺参数对TiC涂层形成的影响

采用液相脉冲放电技术对机械切削加工工具材料表面进行改性,具有很大的经济效益.将高熔点金属Ti电极置入含碳的液相介质中,利用脉冲放电所产生的低温高能等离子体在45钢基体上沉积TiC陶瓷涂层.讨论了脉冲放电工艺参数对涂层形成与涂层硬度的影响.结果表明:脉冲宽度和峰值电流是影响涂层沉积的主要因素,脉冲间隔和放电沉积时间对涂层厚度有影响,而对涂层的硬度几乎没有影响;在小峰值电流(8 A)和窄脉宽(12 μs)的条件下,可以获得高硬度的TiC涂层.     

Study on multi-peak behavior of pulsed dielectric barrier discharges in atmospheric-pressure helium

In this work the multi-peak behavior of the dielectric barrier discharge excited by repetitive voltage pulses (pulsed DBD) in atmospheric-pressure helium has been systematically investigated, based on a one-dimensional fluid model. The effects of the parameters of the applied voltage pulse and dielectrics on the multi-peak behavior of the pulsed DBD have been analyzed in detail. The parameters of the applied voltage pulse include voltage growth rate, amplitude, pulse-width, and frequency. The parameters of dielectrics refer to relative permittivity and dielectric thickness. Under the given amplitude of the applied voltage pulse, the number of current pulses presents no monotonic decrease with increasing voltage growth rate, and the dependence of the amplitude of each current pulse on voltage growth rate is different. For a given voltage growth rate, the number of current pulses will increase with increasing applied voltage amplitude, but the amplitude of each current pulse does not vary. In addition, the increase of the pulse-width or the frequency can induce not only later appearance of current pulses and smaller amplitude of the last current pulse at the rising edge of the applied voltage pulse but also larger amplitude of the last current pulse at the falling edge of the applied voltage pulse. Also, the decrease of relative permittivity of the dielectric or the increase of dielectric thickness results in smaller discharge current density and shorter time of charging dielectrics, which may increase the number of current pulses.     

精密电极结构实现小间隙大气压辉光放电离子源

分析了电极结构精密度对大气压辉光放电稳定性的影响,设计并加工了一套高装配精度的线-筒型离子源.内外电极直径分别为0.16mm和4mm.当电压达到-3.5kV时电晕放电开始发生,放电电流波形为典型的特里切尔脉冲;当电压升高至-4.5kV时放电电流变为直流,表明进入辉光状态.通过放电电流波形可以清晰地观察到从电晕放电到辉光放电的过渡过程,并分析了其物理过程.放电实验表明,该装置可以稳定地实现大气压辉光放电,放电电流与施加电压成正电阻特性,而电极之间的电压在放电电流增大的情况下保持不变.这些放电特性与典型的低气压辉光放电一致.放电电流可达毫安量级,电离度较高,可有效提高检测灵敏度.质谱实验表明该离子源可以很好地离子化甲酸、乙酸、苯酚、苯甲酸等化学物质.     

接地电极转动对电极不对称介质阻挡放电的影响

本文的目的是确定接地电极转动对介质阻挡放电的影响.采用不对称电极结构来降低外加的工作电压.实验的结果表明:接地电极静止或转动介质阻挡放电将呈现不同的放电形式和电流波形.文中对其原因进行了讨论.     

Discharge characteristic of nanosecond-pulse DBD in atmospheric air using magnetic compression pulsed power generator

Dielectric barrier discharge driven by repetitive nanosecond pulses can offer highly efficient non-thermal plasma at atmospheric pressure and is widely used for plasma applications. In this paper, the discharge is generated using a compact pulsed power generator based on one-stage magnetic compression. The output pulse can be up to 30 kV with a rise time of about 40 ns and a full width at half maximum of 70 ns. The electrical characteristics of the discharge parameters are studied by the measurement of voltage and current waveforms. The effects of applied voltage amplitude, voltage polarity, pulse repetition frequency, and barrier dielectric on discharge characteristics are investigated, respectively. The experimental results show that the discharge current, discharge power and electron density increase with the increase of the applied voltage, and the pulse repetition frequency has a slight effect on the electrical parameters. Moreover, the discharge current is influenced by the dielectric barrier, but it is not varied with the polarity of applied pulses.     

TEA CO_2激光器中均匀脉冲放电预电离条件的研究

在TEACO2激光器中，由于气压高，很容易形成弧光放电，导致激光作用停止，因此采用预电离技术是十分重要的。在已取得研究成果的基础上，通过考虑电压上升时间产生的影响，分三种情形对TEACO2激光器中均匀脉冲放电的预电离条件进行了研究，确定了预电离电子密度和最大起始极间场强的允许取值范围。对于电极间加上脉冲高压前预电离就已结束的情形，确定了电压上升时间的最大允许值。     

L-胱氨酸复合掺杂聚苯胺材料的电化学性能

采用化学法用苯胺与盐酸和L-胱氨酸掺杂合成聚苯胺，将样品与一定量的导电物质石墨混合，制备成电极材料测定其电极过程的循环伏安特性，详细研究了各种因素对其充放电性能的影响。经电化学性能测试，发现其氧化还原可逆性和稳定性都较好。电极样品在10mA/cm^2充电2h，以2mA/cm^2恒电流、终止电压为1.0V的放电制度下，可持续放电8h。结果表明，本法所制备的聚苯胺掺杂复合电极材料，充放电效率较高，放电容量大，结构稳定。     

Wide-aperture plasma jet source based on low-voltage spark discharge with ferroelectric electrode

Low-voltage vacuum spark discharge initiated at a storage capacitor voltage of 75–600 V using a metal grid cathode situated on the front surface of a polarized ferroelectric (FE) electrode has been experimentally studied. The discharge was initiated when a control voltage pulse with an amplitude of 1 kV and a duration of 100 ns at only negative polarity was applied to the rear FE surface (irrespective of the direction of its polarization vector). Optical measurements showed that the emitting surface area on the cathode increases approximately in proportion to the discharge voltage. According to the collector measurements, the ion plasma flux has slow and fast components, the velocities of which remain almost constant when the discharge current amplitude varies in a wide interval.     

Analysis of residual stresses in particulate reinforced aluminium matrix composite after EDM

This paper reports the effect of properties of three types of particulate reinforced metal matrix composite materials (65?vol.-%SiC/A356·2, 10?vol.-%-SiC–5?vol.-% quartz/Al, 30?vol.-%SiC/A359) and machining parameters on residual stresses induced in the machined surface during powder mixed electric discharge machining. Three electrode materials (Cu, Gr and Cu–Gr) and three machining parameters, namely, peak current and pulse (on/off) duration, are varied to determine the magnitude of induced residual stresses. The result shows that the workpiece, electrode material properties, and pulse off time significantly contribute in the formation of residual stresses. Concentration of reinforced particulates and matrix conductivity also play a vital role in the development of residual stresses. The deposition of disintegrated particles of composite electrode (Cu–Gr) results in high magnitude of residual stresses.     

聚苯胺复合电极的制备及电化学性能研究

以化学法合成导电聚苯胺，研究了氧化剂和掺杂剂以及反应温度和时间对聚苯胺的产率和电导率的影响。在确定的配方和工艺条件下，聚苯胺的合成产率为94％，电导率在5.6S/cm，将合成得到的聚苯胺掺杂导电粉体制备成高分子是合电极材料，在恒电流上进行充放电性能测试。结果表明，开路电位和放电电位较高，在以4mA/cm^2恒电流放电，终止电位为1．2V时，放电时间可持续16.5h，放电容量大。     

On the nature of the Vorob’evs effect in pulse breakdown of solid dielectrics

The Vorob’evs effect consists in certain features of the discharge observed when a solid dielectric in contact with two rodlike electrodes is placed in a liquid dielectric medium and a voltage pulse with increasing front is applied to the electrodes. When the pulse front slope is small, the discharge develops in the liquid over the solid dielectric surface; whereas the discharge at a sufficiently large slope of the pulse front penetrates into the solid and produces its fracture with cleavage of the surface fragments. In order to explain this phenomenon, it is suggested that, at a sufficiently high voltage buildup rate, a displacement current that is related to the motion of the surface discharge plasma passes through a microprotrusion occurring on the electrode surface at the contact site and causes the electric explosion of this microprotrusion. The metal plasma jet generated as a result of this explosion penetrates into the solid dielectric and forms a discharge channel in depth of this material. The surface discharge plasma formed at a small slope of the voltage pulse front closes the electrode circuit, thus preventing the discharge penetration in depth of the solid.     

Performance evaluation of two-stage electrostatic air filter with low-ozone emission corona charger

The ozone emitted from indoor air cleaners with corona chargers is harmful to the human respiratory system. In this study, a functional treatment of the discharge electrode surface was attempted to reduce the level of ozone generation from the corona discharge. The ozone emission level and charger performance were evaluated by measuring the particle removal efficiency and the pressure drop characteristics with the dust loading on the filter. Ozone production from the low-ozone discharge electrode was reduced by approximately 60% compared to conventional discharge electrode, but the corona initiating voltage and discharge current were equivalent to those of the conventional electrode. The particle removal efficiency of a low-grade filter assisted by the corona charger increased to a high-grade filter without a charger. The replacement time for the low-grade filter with the charger was approximately three times longer than that of a high-grade filter.     

Optimization of material removal rate and surface roughness during electric discharge machining of ultra-fine grained Al6082 using Taguchi technique

In the current work, the statistical analysis of various electric discharge machining parameters on Al6082 ultra-fine grained aluminium alloy using Taguchi method has been presented. Repetitive corrugation and straightening (RCS) method was employed to obtain ultra-fine grained aluminium alloy. The electric discharge machining studies were carried out for test variables – pulse off time, pulse on time and current (I). The specimens were machined in dielectric medium with current range of 3 A to 9 A in step of 3 A. Machining features of the samples analysed statistically by adopting the Taguchi's - design of experiments (DOE) methodology. Impact of parameters on material removal rate (MRR) and surface roughness (SR) were examined via signal-to-noise ratio (S/N ratio, expressed in decibel, dB) as well as analysis-of-variance (ANOVA). Outcomes disclose that every selected response explicitly surface roughness (SR) and material removal rate was significantly influenced by parameters. The material removal rate was found to rise with discharge current and decrease with the duration of pulse on time and the duration of pulse off time. On the other hand, the surface roughness increased with increase in peak current and decreased with pulse on time and pulse off time especially. The machining mechanisms were examined by scanning electron microscopy.     

Experimental Investigation and Optimization of Micro-EDMing Process for Silicon Substrates

Microelectrical discharge machining of n-type monocrystalline silicon is investigated in this study through a microgrooving process. The pulse duration, pulse frequency, spark current, and gap voltage are varied in the experiments. The groove geometries and roughness are measured together with the material removal rate and electrode wear ratio. The results have shown that a large and deep groove can be made at high machining rate when a high spark energy condition is applied. This can, however, increase the electrode wear ratio as a consequence, making the process inefficient. A multiresponse optimization, using Grey relational analysis, has been applied. The optimum cut result has shown that good cut quality, high material removal rate, and low electrode wear ratio are achievable from this study.