Attenuation of Electromagnetic Waves by a Plasma Layer at Atmospheric Pressure

Plasma layers at atmospheric pressure, are good broad band absorbers of electromagnetic radiation. However, to get substantial attenuations, two parameters have to be optimized. These are the plasma number density, and the thickness of the plasma layer. It is found that in order to be an effective attenuator of microwave radiation, a plasma layer has to have a number density in the 10¹³ cm^–3 range, and a thickness equal or larger than the wavelength of the incident wave. However, as the frequency increases, the amount of attenuation tends to reach a limiting value directly proportional to the number density.     

Optical Radiation of Atmospheric Pressure Plasma Jets Excited by a Barrier Discharge

Optics and Spectroscopy - The luminescence spectra of plasma jets formed by a barrier discharge at atmospheric pressure in argon–air and helium–air mixtures have been studied...     

大气压放电等离子体柱的光谱研究

大气压放电等离子体柱在飞行器隐身技术方面具有非常重要的应用。利用同轴介质阻挡放电水电极装置,大气压下在氩气中放电产生了长达65 cm的均匀等离子体柱。利用光学方法研究了等离子体柱的放电机理为发光子弹传播。通过测量发现该子弹的传播速度约为0.6×105 m·s-1。采用发射光谱法测量了等离子体柱的发射光谱中谱线强度比随外加电压和驱动频率的变化关系,其相对强度之比表征了电子平均能量。结果表明电子平均能量随外加电压和驱动频率的增加而增加。本工作对大气压下气体放电的工业应用具有一定的意义,在军事飞行器隐身方面具有广阔的应用前景。     

Non-LTE Argon Plasma Composition at Atmospheric Pressure

The knowledge of plasma composition is very important for various plasma applications and the prediction of other plasma properties. Most of the plasma currently used in plasma-aided processing is in the non-LTE (Local Thermodynamic Equilibrium) state. In this paper, the Saha equations, Debye-length equation, lowering-of-ionization-energy equation and pressure-correction equation, used to calculated the non-LTE plasma composition, are analyzed. The recently published theoretical results are compared with experimental data.     

光谱法诊断大气压等离子体电子密度

采用发射光谱方法对大气压氩气介质阻挡放电(DBD)系统中的电子密度进行了诊断。通过考虑放电等离子体中的各种加宽机制, 采用自编的非对称卷积程序对氩原子发射谱线的线型进行分析拟合, 再通过反卷积的方法将各种加宽机制分离开来, 最终将Stark展宽分离出来进行大气压氩气介质阻挡放电电子密度的计算。诊断结果表明, 在大气压氩气介质阻挡放电中当有三个放电丝存在, 电子温度为10000 K时, 电子密度约为4.06×1021 m-3, 诊断结果和模拟结果符合得很好。此方法不仅可以应用在大气压介质阻挡放电中, 还可以用于其他含有非氢气体的大气压等离子体电子密度的测量。     

常压射流等离子体发射光谱研究

使用改进介质阻挡放电装置生成常压射流等离子体,采用光纤光栅光谱仪在300～1 000 nm范围记录了不同放电电压的氩气发射光谱,并比较了空气和氩气常压介质阻挡放电等离子体发射光谱,分析发现氩气发射光谱中的谱线都是氩原子的发射谱线,表明常压射流装置产生的等离子体全部为氩等离子体,而无其他空气成分参与放电。为测量电子激发温度,选用相距较近的763.51和772.42 nm两条光谱线对电子温度进行分析,结果表明电子激发温度的范围在0.1～0.3 eV,而且它还随着放电电压的增加而增加。初步使用“红外测温仪”测量被处理材料表面温度,结果发现材料表面的温度也随着放电电压的增加而增加,范围在50～100 ℃,材料表面温度的变化趋势可以近似表征等离子体宏观温度变化趋势。通过分析常压射流等离子体的温度特性,探讨了常压射流等离子体温度对材料改性研究的意义。     

大气压低温氦等离子体射流的诊断研究

为了加快低温氦气等离子体射流的工程化进程,通过自主设计的同轴式介质阻挡放电等离子体射流发生器,在放电频率10 kHz,一个大气压条件下产生了稳定的氦气等离子体射流。通过分析不同工况下的电压电流波形可以发现单纯增加氦气体积流量只能小幅的增加电流脉冲幅值,而对放电时间、电流脉冲数的影响不大。增加放电峰值电压时电流脉冲幅值会得到较大幅度增加。通过发射光谱法对大气压氦气等离子射流的活性粒子种类、电子激发温度、电子密度进行了诊断。结果表明,大气压氦气等离子体射流中的主要活性粒子为He Ⅰ原子、N₂第二正带系、N+₂的第一负带系、羟基（OH）,H原子的巴尔末线系（H_α和H_β）与O原子,这表明虽然该试验中使用的氦气纯度已达99.99%,但其中仍残留有少量的空气,同时放电时大气中的空气会被卷吸到放电空间发生电离。还可以发现,主要活性粒子的相对光谱强度随氦气体积流量的增加及放电峰值电压的增大均呈现上涨的趋势。选用He Ⅰ原子的四条谱线对不同试验工况下的电子激发温度进行了计算,得到大气压氦气等离子体射流的电子激发温度在3 500~6 300 K之间,电子激发温度随放电峰值电压与氦气体积流量的增大总体上呈现上升的趋势。但由于反向电场的存在,某些峰值电压可能会出现电子激发温度下降的情况;根据Stark展宽原理对大气压氦气等离子体射流的电子密度进行了计算,发现电子密度的数量级可达1015 cm-3,同时增大峰值电压与氦气体积流量均可有效的提高射流中的电子密度。这些参数的研究对氦气等离子体射流在工程实际中的应用具有重要意义。     

A Microwave Air Plasma Source under Atmospheric Pressure

We develop a new cavity with a mode similar to TE13 to produce microwave plasma, named APMPS Ⅱ, which is able to produce a mass of air plasma with diameter of around 6 cm, equipped with about 3 kW input power under one atmosphere. The plasma seems to be homogeneous without significant filamentous discharge as observed by common camera device. We present the theory of this cavity, show the distribution of electric field of several planes inside the cavity and give some experimental results.     

棒-环电极大气压等离子体射流的光谱特性

通过设计新型的交流电压激励的氩气等离子体射流,在棒电极的上游与下游区域均产生了大气压非平衡态等离子体羽。该射流与平行场射流和交叉场射流不同,它的电场与气流方向的夹角可以在一定范围内变化。结果表明,随着外加电压或夹角的增加,上游羽的长度增加而下游羽的长度减小。利用光学和电学的方法,研究发现随着外加电压的增加,上下游放电脉冲的个数均增加。利用放电的光学发射谱,发现上游羽有Ar和OH的谱线,而下游羽除了Ar和OH的谱线外,还可以观察到N₂的谱线。并且下游羽的谱线强度比上游羽的略高。基于碰撞辐射模型,通过谱线强度比的方法研究了上下游羽的电子密度和电子激发温度。结果表明上下游羽的电子密度随着外加电压的增加而增加。上下游羽的电子激发温度也随着外加电压的增加而增加。并且,在同一外加电压时下游羽的电子密度和电子激发温度均比上游羽的高。此外,利用OH发射光谱研究了上下游羽的气体温度,发现下游羽的气体温度也比上游羽的略高。     

常压介质阻挡放电等离子体发射光谱的检测分析

以常压介质阻挡放电等离子体作为研究对象,在常温常压条件下使用介质阻挡放电光谱诊断装置,得到N2第二正系跃迁和Ar原子发射谱线。通过对放电光谱的检测分析,可以察知常压介质阻挡放电等离子体的特性,并可运用同一元素谱线的相对强度来诊断电子激发温度等物理参量,以达到对材料表面改性过程的实时监控,工作的结果对常压介质阻挡放电及其在材料改性的应用中具有重要的意义。     

大气压直流氩等离子体光谱诊断研究

通过光谱诊断系统测量了大气压直流氩等离子体射流在弧室内和弧室出口的发射光谱,利用波尔兹曼曲线斜率法计算了射流的电子温度,根据Ar Ⅰ谱线的斯塔克展宽得到射流的电子密度,并对氩等离子体射流满足局域热力学平衡(LTE)状态的判定标准进行了分析,结果表明在文章的实验条件下大气压直流氩等离子体射流达到局域热力学平衡。     

大气压空气等离子体羽的振动温度研究

利用三电极介质阻挡放电装置,在大气压空气中产生了较大体积的等离子体羽。采用光学方法对该等离子体羽的特性进行了研究。发现随着外加电压峰值增加,每个外加电压周期的放电脉冲个数增加。通过采集等离子体羽的发射光谱,空间分辨地研究了放电等离子体羽的振动温度。结果表明等离子体羽的振动温度随着外加电压峰值的增加而减小;随着远离喷嘴的距离的增加,等离子体振动温度先增加后减小,当距离喷嘴5.4 mm时振动温度达到最高值。对上述现象进行了定性分析。研究结果对大气压空气等离子体羽在杀菌消毒等领域的应用具有重要意义。     

大气压空气脉冲流光放电等离子体发射光谱分析

在大气压条件下采用尖-尖电极放电系统得到了稳定的放电等离子体, 并应用发射光谱方法对放电等离子体进行了实验研究。等离子体发射光谱呈现连续谱背景迭加分立谱的形式。连续谱背景来源于放电等离子体内轫致辐射和复合辐射过程; 分立谱归属为N2 C3∏u →B3∏g , N+, N, O的荧光辐射。N+荧光辐射对应的上能级电子组态为2s22p(2P0)3p和2s22p(2P0)3d, 能级高度介于20 eV和23.6 eV之间。实验还结合时间分辨光谱技术, 对放电等离子体中N2(336.8 nm)、N+(500.5 nm)、N+(399.7 nm)荧光信号进行时间分辨测量。结果表明, N2(336.8 nm)荧光首先出现, N+(500.5 nm、399.7 nm)荧光同时产生, 且滞后N2(336.8 nm)荧光约25 ns。根据时间分辨测量结果和相关参考文献, 文章对放电等离子体中N+的生成通道进行了分析。     

The Uniform Si-O Coating on Cotton Fibers by an Atmospheric Pressure Plasma Treatment

A uniform Si-O coating on cotton fabric was produced at atmospheric pressure by a plasma treatment. Before the plasma discharge, a pretreatment with hexamethyldisiloxane (HMDSO)-ethanol mixture solvents on the fabric was employed. The surface morphology and chemical structure of the plasma-treated fibers were analyzed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses. The SEM results showed that a uniform, continuous film was formed on the cotton fiber surface. It was much rougher than the uncoated fiber. The FTIR results showed that the coatings contained most of the Si-O functional groups. These Si-O bonds, broken from the Si-O-Si functional groups by the plasma electron impact, had connected with the cellulose by chemical bonds of Si-O-Cellulose. XRD patterns revealed the existence of a crystalline structure within the thin coating film. The UV-vis transmission of the cotton textile was greatly reduced by such coatings.     

直流激励的大气压氩气喷枪的光谱研究

利用正高压驱动空心针-板喷枪装置,通入工作气体氩气,在大气压空气中产生了均匀稳定的喇叭状等离子体羽。电学和光学测量结果表明,放电虽然是在直流电源驱动下工作,但放电为周期性的脉冲。通过对等离子体羽发光信号进行空间分辨测量,研究了脉冲的形成机理,发现除针尖附近的电晕放电外,等离子体羽是以正流光(等离子体子弹)从针尖向着接地电极方向传播的。采用光谱学方法,对电子激发温度随电压的变化及其空间分布进行了测量。结果表明,电子激发温度(约为3 eV)随电压的增大而升高,在一定电压下,电子激发温度沿气流方向也在升高。     

Atmospheric Pressure Plasma Application for Pollution Control in Industrial Processes

Economic application of atmospheric pressure plasma technology for industrial pollution control requires fulfilling two propositions: First application of pollution control technologies needs to result in clear environmental, health, or safety benefits motivating political measures. Second plasma technology needs to be competitive as compared to other available pollution control technologies. Thus in this article methods for the evaluation of atmospheric plasma application for industrial pollution control are reviewed: Examples of emission regulations and emission control technologies are given. Requirements of industrial scale emission control and of thermal and non‐thermal exhaust gas treatment technologies are described. The potential of various non‐thermal plasma reactor concepts for cost effective treatment of industrial scale gas flows is analyzed, and methods for the evaluation of plasma energy balance and plasma chemical kinetics are given for them. How to deal with shortcomings of atmospheric pressure plasmas such as lack of plasma‐chemical selectivity is addressed in a section about plasma‐catalytic hybrid processes. Further the progress made recently in electrostatic precipitation is reviewed, and the importance of electro‐hydrodynamic effects for the reactor design both for electrostatic precipitation and for plasma chemical pollution control is considered. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)