介质阻挡放电中微放电周期特性的光学测量

采用特殊设计的双水电极介质阻挡放电装置,利用光学方法原位、无干扰地测量了大气压空气介质阻挡放电中微放电的单脉冲特性和周期特性,实验上首次发现在介质阻挡放电斑图模式中,微放电在驱动电压的正负半周的放电时刻并不是固定的,相邻两次放电的时间间隔是长短交替的。根据壁电荷对微放电通道相邻两次放电的不同作用,分析了相邻两次放电时刻的联系,很好地解释了相应的实验现象。     

Impact of Electrode Design,Supply Voltage and Interelectrode Distance on Safety Aspects and Characteristics of a Medical DBD Plasma Source

In the frame of plasma source development for dermatological applications in the field of plasma medicine, operational safety of the devices is of superior priority. For sources based on the concept of dielectric barrier discharges (DBD), electric potentials with amplitudes in the range of some kV are arranged in close proximity to the skin of patients, wherein dielectric strength of the electrodes and leakage currents are crucial for electrical applicability. In this work, ceramic electrodes of 10 mm in diameter and varying ceramic thickness are operated at input powers up to 300 mW against non‐biological counter electrodes. In a combined experimental and numerical approach, electric fields inside the ceramic are determined, whereas values are well below the dielectric strength of the material. The spectrally weighted plasma emission is within limit values of exposure to human skin as long as daily treatment does not exceeded 7 h. Neutral gas temperatures of up to 310 K are determined which underline the minor thermal impact of the plasma exposure. In contrast, values for reduced electric fields are of the order of some hundred Townsend and thus the electrons can initiate various secondary effects such as chemical reaction chains. Consequently, ozone concentrations in the discharges are quantified between 230 ppm and 1140 ppm in close proximity to the actual discharge volume and the results are discussed in the frame of risk assessment for therapeutic applications in dermatology. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Neutralization of charged dielectric materials using a dielectric barrier discharge

Safety and efficiency are two characteristics that must be satisfied by an electric charge neutralizer. The dielectric barrier discharge (DBD), which has the advantage of preventing arc transition, is an interesting tool to safely neutralize unwanted charge. This paper is aimed at studying the efficiency of neutralizing charged polyethylene (PE) granules by using a dielectric barrier discharge. During this study, several factors were considered such as the amplitude and the frequency of the AC voltage, the polarity and the charging mode of the samples, as well as the electrode configuration. Two DBD electrode configurations were considered: simple DBD and a DBD with installed metallic grid. The obtained results show that using the DBD can lead to excellent neutralization results when the grid is installed. With the appropriate voltage amplitude and frequency and with grid installed, the elimination of nearly 99% of the initial surface charges can be achieved. The metallic grid placed between the DBD electrode and the target enhances significantly the neutralization efficiency.     

Properties of surface dielectric barrier discharge plasma generator for fabrication of nanomaterials

This paper presents surface dielectric barrier discharge plasma generators as an efficient source of low-energy ions. Either positive or negative ions can be extracted from a plasma cloud with an external DC field created by the third electrode. Three different cross-section geometries of DBD generators were analyzed, simulated and fabricated. Currents of ions extracted from the plasma cloud were measured and the results were discussed. It was demonstrated that if the third electrode consists of liquid–gas interface, the presented arrangement can be used as a versatile reactor for nanomaterial synthesis (on the example of the synthesis of silver nanoparticles).     

The influence of the discharge parameters on the plasma spatial structuring in argon DBDs

The plasma parameters, discharge plasma uniformity and filamentation processes in high pressure (near atmospheric pressure) dielectric barrier discharges (DBD) in argon are studied using the developed two-dimensional 2D(r, z) model. The applied voltage frequency, the voltage shape, the dielectric layers material and its thickness are varied and the effects of such variations on plasma uniformity, discharge structure and operation are studied. The DBD discharges with different dielectric layers thickness, dielectric constants and secondary electron emission coefficients are simulated. It was shown that the dielectric layer thickness is an important parameter for producing high pressure discharges uniform over the radius. The possibility of the radially uniform discharges at atmospheric pressure was shown in the present study.     

Influence of Gap Spacing between Dielectric Barriers in Atmospheric Pressure Discharges

The breakdown activity in helium atmospheric pressure dielectric barrier discharge (DBD) plasma is strongly modified by introducing small impurities (nitrogen (N₂) and air in ppm), although its precise implications for the behavior of discharge plasma is not evident under several constraints. In this simulation study, we investigate the influence of gap spacing between the dielectric barriers to explore the dynamic modification in the structure of discharge plasma in distinct phases of the discharge current pulse using a two‐dimensional fluid model in He‐air gas mixture. Specifically, the impact of nitrogen and air impurities is contrasted by exploring the spatial distributions of electrons in the breakdown phase under similar operating conditions. The filamentary mode of DBD plasma in He‐N₂ is transformed into uniform glow discharge in He‐air gas mixture by the dominant effect of Penning ionization. Finally, the outcomes of two‐dimensional fluid model are validated by comparing with three‐dimensional fluid model to provide the reliability of numerical simulations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionic wind produced by an electro-aerodynamic pump based on corona and dielectric barrier discharges

The present study aims at showing the ability of ac discharges to be used as fanless blower in a rectangular channel. First, a 10 mm-high channel is used with four different types of ac atmospheric air discharges: an ac wire-to-plate corona discharge, two different ac wire-to-plate dielectric barrier discharges (DBD) and a surface DBD. The electrical and mechanical characteristics of the four different discharges are investigated and compared. They highlight that the best geometrical configuration is the wire-to-plate DBD with a thick dielectric, that allowed us to induce ionic wind velocity up to 3.3 m/s and flow rate per unit spanwise length of 24 L per second per meter. Secondly, this optimized configuration is reduced in size (2 mm-high channel) and the effect of this downscaling on the plasma actuator performances is studied, showing that the efficiency decreases with the channel height.     

Highly time-resolved investigation of the electric wind caused by surface DBD at various ac frequencies

Surface plasma discharges find relevant applications for manipulating laminar or turbulent flows. The control mechanism can be related to time-averaged momentum transfer or be associated to favorable interactions between the fluctuations imposed by the discharge and the natural instabilities developing in the incoming flow. In the present paper, the electric wind produced by a non-thermal surface dielectric barrier discharge is investigated by a non-intrusive measurement technique having a high temporal resolution. The measurements are carried out for an actuator in quiescent flow condition, but also for an actuator placed in the test section of a wind tunnel with external flow speed from 5 to 30 m/s. The results confirm that a surface DBD actuator has a low control authority on the mean characteristics of the velocity profiles developing above the plasma region. However, it is also demonstrated that the plasma actuator imposes periodic fluctuations at the electrical frequency driving the gas ionization, this over the whole range of tested speeds.     

Effect of atmospheric pressure dielectric barrier discharge air plasma on electrode surface

In order to study the influence of plasma on electrode, atmospheric pressure dielectric barrier discharge (DBD) air plasma is employed here to treat copper electrode surface. Plasma is generated between the parallel plate electrodes by means of high voltage produced by a high-frequency power supply with transformer. Electrode surface alterations induced by air plasma are investigated by using field emission scanning electron microscope (FE-SEM), X-ray energy dispersion spectroscopy (EDS) and contact angle measurement. The results show that DBD air plasma removes the organic contaminant on surface and causes electrode surface roughness, oxidization and nitridation. In addition, surface wettability is also improved, as concluded from contact angle measurements.     

气压对微束射频容性放电模式调制的研究

微束射频容性放电在纳米晶体颗粒等离子体增强气相合成有着潜在的应用前景.本论文利用ICCD、单反相机、高压探头和电流探头等对微束射频容性放电特性进行了实验诊断研究.结果发现:在纯氩气微束射频放电中,随着气压的增加,放电从辉光放电模式向多通道丝状放电模式转换;在99%氩/1%氢混合气体微束射频放电中,丝状放电模式消失,而是从低气压全空间分布的辉光放电模式,到中等气压向轴心收缩的辉光放电模式,最后到高气压的“环状”辉光放电模式;而在纯氢气微束射频放电中,随着气压的增加,放电模式直接从全空间分布的辉光放电模式向“环状”辉光放电模式转换.最后通过射频电场中电子加热、趋肤效应和气体热传导的共同作用解释了产生不同放电模式的物理机制.     

Uniformity analysis of dielectric barrier discharge (DBD) processed polyethylene terephthalate (PET) surface

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of polyethylene terephthalate (PET) films. The effects that the key DBD operating parameters: discharge power, processing speed, processing duration, and electrode configurations, have on producing wettability changes in the PET surface region have been investigated. The approach taken involves the application of an Taguchi experimental design and robust analysis methodology. The various data sets obtained from these analyses have been used to studies the effect of the operating parameters on the surface uniformity and efficiency of the said treatment.In general, the results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PET. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the polymer film surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, there was significant differences between the data obtained from these two orientations. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the electrode configuration used were found to have the most significant effects on the homogeneity of the resultant PET surface changes in L- and T-orientation, respectively. On the other hand, the applied power showed no significant role in this regard. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PET surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicon rubber-covered aluminium plate (see later). The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. Thus, it was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PET, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence.     

不同电极结构下介质阻挡放电电离特征的试验研究

由于具有工作气压高、放电均匀等特点,大气压介质阻挡放电成为近年来非平衡等离子体领域研究的主要技术。电极结构是电离特性的主要影响因素之一,因此,通过电极结构优化来改善电离特性,对等离子体放电设备的应用领域拓展及性能优化至关重要。为改善大气压介质阻挡放电的电离特性,产生高活性、高均匀性的低温等离子体,基于自主设计的同轴介质阻挡放电装置进行了不同电极结构的电离试验及参数诊断;在一个标准大气压、放电频率11.4 kHz、放电峰值电压5.4～13.4 kV条件下进行了氩气电离试验;采用原子发射光谱法（AES）对氩等离子体谱线的激发、分光进行了检测分析;研究了螺纹电极、齿状电极、圆柱电极放电的特征光谱参数及外施电压对介质阻挡放电特征参数的影响。结果表明,齿状电极放电所形成等离子体的放电强度更大且放电效果显著,电子平均能量利用率低,电子激励温度弱于圆柱电极;圆柱电极放电强度较弱,但易形成大面积均匀性等离子体;大气压环境下电子激励温度不因外源电压的升高而单调递加,这表明通道内微放电的主要特征并不依赖于外施电压的供给,而是取决于电极结构、气体组份、气体压强;增大外施电压仅能增加单位时间内微放电的数量,经整合电子激励温度可达3 500 K,符合典型的低温等离子体特征。     

介质阻挡放电低温等离子体脱硝性能研究

进行了介质阻挡放电低温等离子体脱除伴有SO₂的烟气中NO的研究,分别进行了直接等离子体脱硫脱硝和间接等离子体脱硫脱硝实验。在直接等离子体脱硫脱硝中,模拟烟气等混合气直接通入等离子体发生器,在反应器中电离分解NO以及和生成的高能电子、离子和自由基等离子体相互反应而进行脱除NO;间接等离子体脱硫脱硝中,模拟烟气连接在等离子体发生器出口与从反应器中产生出的等离子体发生氧化反应而进行脱除NO。结果表明,无论直接形式还是间接形式,脱硝效率都要比脱硫效率高,间接脱硫脱硝能够大大降低功率输入,节省能耗,具有重要的实际应用价值和意义。氨气的加入,有利于脱除效率的提升。     

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进行了介质阻挡放电低温等离子体脱除伴有SO2的烟气中NO的研究,分别进行了直接等离子体脱硫脱硝和间接等离子体脱硫脱硝实验.在直接等离子体脱硫脱硝中,模拟烟气等混合气直接通入等离子体发生器,在反应器中电离分解NO以及和生成的高能电子、离子和自由基等离子体相互反应而进行脱除NO;间接等离子体脱硫脱硝中,模拟烟气连接在等离子体发生器出口与从反应器中产生出的等离子体发生氧化反应而进行脱除NO.结果表明,无论直接形式还是间接形式,脱硝效率都要比脱硫效率高,间接脱硫脱硝能够大大降低功率输入,节省能耗,具有重要的实际应用价值和意义.氨气的加入,有利于脱除效率的提升.     

Numerical study on the discharge characteristics and nonlinear behaviors of atmospheric pressure coaxial electrode dielectric barrier discharges

The discharge characteristics and temporal nonlinear behaviors of the atmospheric pressure coaxial electrode dielectric barrier discharges are studied by using a one-dimensional fluid model. It is shown that the discharge is always asymmetrical between the positive pulses and negative pulses. The gas gap severely affects this asymmetry. But it is hard to acquire a symmetrical discharge by changing the gas gap. This asymmetry is proportional to the asymmetric extent of electrode structure, namely the ratio of the outer electrode radius to the inner electrode radius. When this ratio is close to unity, a symmetrical discharge can be obtained. With the increase of frequency, the discharge can exhibit a series of nonlinear behaviors such as period-doubling bifurcation, secondary bifurcation and chaotic phenomena. In the period-doubling bifurcation sequence the period-n discharge becomes more and more unstable with the increase of n. The period-doubling bifurcation can also be obtained by altering the discharge gas gap. The mechanisms of two bifurcations are further studied.It is found that the residual quasineutral plasma from the previous discharges and corresponding electric field distribution can weaken the subsequent discharge, and leads to the occurrence of bifurcation.     

大气压氖气介质阻挡放电脉冲等离子射流特性

采用自行研制的低造价、小体积、可产生幅值0~35 kV、重复频率1 kHz的高压s脉冲电源,设计了一套以大气压氖气为工作气体的介质阻挡放电（DBD）等离子体射流源,通过测量并计算放电过程中的电压-电流波形、拍摄放电图像、光谱分析等手段,对电压幅值、气体流速对氖气等离子体射流特性的影响进行了研究。结果表明:s脉冲电源激励下大气压氖气DBD能产生锥状的等离子射流且其等离子强度适中;s脉冲电源电压幅值的快速上升,可在放电空间瞬间施加高的过电压,能有效促进放电功率、电子密度、电子激发温度和射流长度的增加;工作气体流速的增加使得放电功率、电子激发温度和电子密度减小,而射流长度变化很小;一定条件下,能形成长距离的射流。     

Spatial Uniformity of Atmospheric Pressure Discharges: A Simulation Study

Spatial uniformity is important in most applications of dielectric barrier discharges operating at atmospheric pressure. However, such uniformity is not easily achieved. Under many conditions, a filamentary structure usually develops. In this paper, we employ a two‐dimensional self‐consistent fluid model to explore the influence of several factors on the evolution of spatial structure of dielectric barrier discharges. In particular, we contrast the behavior of discharges in pure helium and He‐N₂ gas mixture, which represent the reduction in breakdown voltage of gas during the evolvement of uniform glow discharge plasma. The transformation from filamentary to uniform mode of discharge plasma is analyzed by the phenomenon of coalescence of filaments and we investigate the effect of several external discharge parameters, such as driving frequency and effect of overvoltage, and the dielectric constant of the barrier material for the uniform and filamentary discharge plasmas. This simulation study is useful to describe the spatio‐temporal profiles of electron density in different phases of the filamentary, uniform Townsend and glow discharge regimes under various constraints. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

同轴介质阻挡放电发生器介质层等效电容和负载特性研究

大气压介质阻挡放电(DBD)可以在常压下产生非平衡等离子体,已经成为热点研究领域.通过脉冲或交变电源激发放电,研究电源输出特性、电源与放电发生器负载间的匹配和外界条件对放电的影响对于理解放电现象和提高放电效率具有重要意义.本文采用Lissajous图形法,分别研究了驱动电压、气流速率等因素影响同轴DBD发生器介质层等效电容及负载幅频特性的规律.结果表明,气流速率和驱动电压等外界条件影响DBD发生器的负载特性:介质层等效电容随气流速率增大而减小,随驱动电压增大而增大;幅频特性曲线均表现出RLC回路谐振现象,谐振频率随气流速率增大而增大,随驱动电压增大而减小.通过对比发现,介质层等效电容随频率的变化曲线与幅频特性曲线具有一致的特征,介质层等效电容是影响电路谐振频率动态变化的主要因素.提出了一种有关介质层等效电容的形成机制.     

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The electric field strength and electron mean kinetic energy in co-axial dielectric barrier discharge (DBD) were estimated based on static electric filed model. Through the comparison of the single dielectric layer DBD with the double dielectric layer DBD, it was found the electric field strength and electron mean kinetic energy in double dielectric layer DBD are greater than that in the single dielectric layer DBD under the same electrode configuration and discharge conditions. The calculation results can successfully applied to explain the toluene degradation efficiency in double dielectric layer DBD is larger than that in the single dielectric layer DBD under the same discharge parameters.     

估算线筒式介质阻挡放电场强和电子平均动能的方法

利用静电场模型对线筒式介质阻挡放电电场强度进行了计算,并对电子平均动能进行了估算。通过对单双介质阻挡放电(DBD)的对比,发现在相同的放电条件下,双介质DBD产生的电场强度和电子平均动能比单介质DBD的要大。这就很好地解释了在相同的放电参数下,甲苯的降解效率在双介质DBD中要比单介质DBD中大。