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.     

The effect of air plasma on barrier dielectric surface in dielectric barrier discharge

Barrier dielectric is an important part of atmospheric pressure dielectric barrier discharge (AP-DBD), which partly affects discharge characteristics. Conversely, discharge plasma also has influence on dielectric surface properties. To investigate this influence, some experiments were carried out on a home-built AP-DBD system with glass plate as barrier dielectric. Surface wettability was evaluated by water contact angles on a drop shape analysis system. The morphologies and chemical compositions of the glass sample surfaces were observed by field-emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS) attached to FESEM. The results show that water contact angles decrease as discharge energy increases, micro-discharge etching zones are formed into glass surface and different from the control glass in surface micro-structure and chemical compositions.     

Equilibrium configurations of the conducting liquid surface in a nonuniform electric field

Possible equilibrium configurations of the free surface of a conducting liquid deformed by a nonuniform external electric field are investigated. The liquid rests on an electrode that has the shape of a dihedral angle formed by two intersecting equipotential half-planes (conducting wedge). It is assumed that the problem has plane symmetry: the surface is invariant under shift along the edge of the dihedral angle. A one-parametric family of exact solutions for the shape of the surface is found in which the opening angle of the region above the wedge serves as a parameter. The solutions are valid when the pressure difference between the inside and outside of the liquid is zero. For an arbitrary pressure difference, approximate solutions to the problem are constructed and it is demonstrated the approximation error is small. It is found that, when the potential difference exceeds a certain threshold value, equilibrium solutions are absent. In this case, the region occupied by the liquid disintegrates, the disintegration scenario depending on the opening angle.     

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.     

Preparation of hydrophobic coating on glass surface by dielectric barrier discharge using a 16 kHz power supply

A 16 kHz power supply was used to investigate the preparation of hydrophobic film on glass surface by means of atmospheric pressure dielectric barrier discharge (DBD). Air nonthermal plasma was induced between the two parallel electrodes with a glass plate as dielectric barrier. The process for hydrophobic film includes two parts: one is plasma pretreatment to produce active layer on glass surface, another is to form hydrophobic film on glass surface by means of the interaction between air plasma and polydimethylsiloxane oil. The surface changes were observed using contact angle measurement and atomic force microscope. The results show DBD can increase surface roughness, and effectively improve glass surface activation and form a hydrophobic coating on glass surface, and it is possibility to prepare hydrophobic glass with middle frequency power supply.     

Photonic-crystal properties of a 1D longitudinally magnetized periodic structure

Features of propagation of circularly polarized waves in a plane-layer periodic longitudinally magnetized ferromagnet—dielectric structure are studied. Dispersion relations and reflection coefficients are obtained, and frequency dependences of the Bloch wavenumber and reflection coefficients are constructed for natural waves of the periodic structure under investigation. The dependences of the polarization plane rotation angle in the polar Kerr effect on the frequency and the ratio of the thicknesses of layers over a period are constructed for various numbers of periods in the structure.     

Active plasma grid for on-demand airflow mixing increase

The present paper concerns the electromechanical characterization of an actuator composed of a ceramic plate perforated by 121 holes housing embedded and printed electrodes between which a high voltage is applied. The electrode arrangement is such that the holes where the gas flows are surrounded by surface discharges. Electrical measurements and iCCD images show that the discharge behaves as a typical surface dielectric barrier discharge with streamer and glow regimes during one period of the AC sine voltage. Particle image velocimetry has been used to measure the jet flow produced by the discharge. The plasma discharge is at the origin of a wall jet with mean velocity of about 2.2 m/s, oriented from the active electrode to the grounded one. The capability of this discharge for promoting mixing by reducing the length of the jet core is demonstrated for flow velocities from 20 up to 60 m/s. In all the tested cases, the actuator can improve the mixing downstream of the perforated plate, when periodic perturbations are imposed at the jet column mode (St_D = 0.3).     

Peculiarities of the spectral-angular distribution of transition radiation from a relativistic particle in a dihedral angle

The spatial distributions of transition radiation from relativistic particles entering and exiting the edge of a dihedral angle formed by perfectly conducting flat surfaces have been investigated. The angular distributions of the radiation intensity in dihedral angles with various opening angles have been calculated. The angular distributions of forward radiation (when the particle exits the dihedral angle) and backward radiation (when the particle enters the dihedral angle) are shown to differ significantly.     

Conversion of environmental heat to electric energy in the metal-dielectric-semiconductor-metal system

The basis of the proposed converter is a thermoelectric capacitor, which is the system of a metal-dielectric-semiconductor-metal. In such a system, non-zero conversion of the environmental heat into electrical energy without preliminarily creating a temperature gradient is possible. Charging of the thermoelectric capacitor takes place through the bottom electrode of the semiconductor substrate and discharging takes place through the near-surface layer enriched electrons formed during charging in the near-surface layer on the boundary with the dielectric. In this case, the amount of absorbed heat at the capacitor charging in the contact of the metal-semiconductor is greater than being allocated heat at the discharge. This is due to the fact that the contact difference between the bottom electrode and semiconductor is more than the contact difference between the metal and near-surface enriched layer in which the concentration of electrons is significantly more than in the volume of a semiconductor. As a result, the absorbed heat, which is not emitted, is converted into electrical energy at the discharge according to the law of conservation of energy.     

Transition radiation in a dihedral angle formed by perfectly conducting planes

The spatial distribution of the field of transition radiation generated by a relativistic particle flying into a dihedral angle formed by perfectly conducting plane surfaces is determined. The cases when particles are injected from the edge and from a plane of the dihedral angle are considered. The angular distributions of radiation intensity in dihedral angles of different values are calculated.     

Effect of plasma treatment of the dielectric on electroforming of a thin-film MIM system

It was found that when a thin dielectric film is exposed to the plasma of a low-voltage gas discharge, channels with elevated conductivity form in the film and these channels significantly facilitate the subsequent electroforming of the MIM system. It is concluded from the experimental data that even in the case of metallic electrodes highly conducting channels are formed in the dielectric by electronic processes occurring under the conditions of a strong electric field and not by diffusion of the electrode material.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 94–98, October, 1991.     

最大负荷设计之：角区分离预测与控制

角区分离对叶轮机性能有重要影响.本文根据角区流动特征推导出描述角区三维附面层的等效二维附面层模型,并结合二维附面层分离准则,建立了角区分离判定准则.理论分析表明:为抑制角区分离,应尽量增大叶表吸力面与端壁相交二面角;为抑制角区分离,应使二面角α沿流向逐渐增大,或使二面角α沿流向逐渐减小过程尽量平缓,尤其在二面角α较小区域更应如此.鉴于此,建议风扇/压气机设计中应严格监控角区二面角大小及二面角流向变化梯度,以实现对角区分离的良好控制.结论也适用于其它叶轮机.     

Energy and mass compositions of the plasma of a nanosecond coaxial vacuum surface discharge

The energy and mass compositions of the plasma generated by a nanosecond coaxial discharge on the surface of high-pressure polyethylene at different polarities of the central electrode with and without a vacuum gap between the dielectric and the peripheral electrode are investigated. It is shown that a nanosecond coaxial discharge on a dielectric surface is an efficient source of high-energy multicharged ions.     

A DC corona discharge on a flat plate to induce air movement

This paper describes a DC surface corona discharge designed to modify the airflow around a flat plate. The electrode configuration consisted of two thin copper layers placed on each side of the plate's attack edge. Discharge optical measurements with a photomultiplier tube indicated that the light emitted by the plasma is pulsating at a frequency that increases with applied voltage. Moreover, with voltage higher than a threshold value, the electric discharge changes regime with brighter pulses. This discharge also induced an “ionic wind” whose velocity was measured with a pressure sensing probe (up to 1 m/s). Experiments with the particle image velocimetry system in a subsonic wind tunnel showed that this discharge can reduce the separated airflow on the flat plate for a flow of 14 m/s (Reynolds number of 187,000).     

Lamb wave dispersion in a PZT/metal/PZT sandwich plate with imperfect interface

Abstract

The Lamb wave dispersion in a PZT/Metal/PZT sandwich plate is investigated by employing the exact linear equations of electro-elastic waves in piezoelectric materials within the scope of the plane-strain state. It is assumed that at the interfaces between the piezoelectric face layers and metal core layer, shear-spring and normal-spring type imperfect conditions are satisfied. The degree of this imperfectness is estimated through the corresponding shear-spring and normal-spring type parameters which appear in the contact condition characterizing the transverse and normal displacements’ discontinuity. The corresponding dispersion equation is derived, and as a result of the numerical solution to this equation, the dispersion curves are constructed for the first and second lowest modes in the cases where the material of the face layers is PZT and the material of the middle layer is Steel (St). Consequently, for the PZT/St/PZT sandwich plate, the study of the influence of the problem parameters such as the piezoelectric and dielectric constants, layer thickness ratios, non-dimensional shear-spring, and normal-spring type parameters, is carried out. In particular, it is established that the imperfectness of the contact between the layers of the plate causes a decrease in the values of the wave propagation velocity.     

Spectroscopic investigations of back-corona discharge on fly-ash layer

Results of spectroscopic investigations of back discharge generated in point-plane electrode geometry in ambient air at atmospheric pressure are presented in the paper. The back discharge was generated for the plate electrode covered with fly ash layer. To characterize the discharge process, the emission spectra were measured for the back discharges and compared with those obtained for corona discharge generated in the same electrode configuration but with dielectric layer removed. The measurements have shown that spectral lines emitted by the back discharge depend on the forms of discharge and the discharge current. From comparison of spectral lines of back and normal discharges an effect of the dust layer on discharge morphology can be determined. In normal conditions, the emission spectra are dominated by atmospheric components (molecular nitrogen, atomic oxygen and nitrogen) but for back-discharges, additional lines due to elements and compounds in fly ash were also identified. The studies of back discharge were undertaken because this type of discharge decreases the collection efficiency in electrostatic precipitators.     

Fabricating a reactive surface on the fibroin film by a room-temperature plasma jet array for biomolecule immobilization

A simple dielectric barrier discharge(DBD) jet array was designed with a liquid electrode and helium gas.The characteristics of the jet array discharge and the preliminary polymerization with acrylic acid(AA) monomer were presented.The plasma reactor can produce a cold jet array with a gas temperature lower than 315 K,using an applied discharge power between 6 W and 30 W(V dis × I dis).A silk fibroin film(SFF) was modified using the jet array and AA monomer,and the treated SFF samples were characterized by atomic force microscopy(AFM),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and contact angle(CA).The deposition rate of the poly acrylic acid(PAA) was able to reach 300 nm/min,and the surface roughness and energy increased with the AA flow rate.The FTIR results indicate that the modified SFF had more carboxyl groups(-COOH) than the original SFF.This latter characteristic allowed the modified SFF to immobilize more quantities of antimicrobial peptide(AP,LL-37) which inhibited the Escherichia coli(E.Coli) effectively.     

Comparison of different electrode arrangements for gas decomposition efficiency using experimental method

The environmental pollution is a central issue in the present industrial societies. Within that the air pollution and the removal of hazardous components of flue and exhaust gases are very much important.In this paper the target is to decrease of the NO_x emission by means of a technology similar to that is used in the electrostatic precipitators. In most of the papers dealing with this technique cylindrical precipitator is used as a discharge chemical reactor, and fast rising electric discharges are applied for energizing the reactor. In the industry the over helming majority of the electrostatic precipitators are plate type one.In the cylindrical precipitator the discharge electrode is parallel with the gas flow, and the corona discharge filament is perpendicular to both of them. In the case of plate type industrial electrostatic precipitator the discharge electrodes are positioned vertically, and the flow of the flue gas is horizontal. Consequently, the discharge filaments are mainly perpendicular to both the flow and the discharge electrode.In cylindrical precipitator the decomposition of NO_x is done in one filament very soon, but there is no chance to modify the byproducts with a new pulse, because the energization is the same for the whole length of the discharge electrode.In the present paper a cylindrical precipitator, a plate type precipitator with horizontal electrode, and a plate type precipitator with vertical electrode were tested. The total length of the discharge electrodes of all of the precipitators was the same.The results of the NO_x decomposition were experimentally determined, and the differences between the precipitators were investigated. The cylindrical and the plate type precipitators with vertical electrodes had shown basically similar decomposition rate, while the plate type one with horizontal discharge electrode had proven inferior to the others.     

Experimental study of coherent transition radiation from relativistic electrons in a dihedral angle

Angular intensity distributions for transition radiation excited by a beam of relativistic electrons in the emitter in the form of a dihedral angle are measured in the millimeter range. The angle is formed by the intersection of two conducting planes. The source of radiation is a microtron with an electron energy of 7.4 MeV. We analyze the effect of the magnitude of the dihedral angle of the emitter, the position of the electron transition point on the surface of the angle, and the direction of motion of electrons on the angular distribution of radiation intensity. It is shown that the spectral and angular distributions of radiation intensity in the dihedral angle substantially differ from analogous distributions for a particle intersecting a planar conducting surface. The possibility of using radiation to measure the energy, spatial position, and direction of motion of charges is considered.     

纳秒脉冲空气辉光放电等离子体及应用

采用基于半导体断路开关的纳秒脉冲高压电源,在两个金属电极之间产生放电区间为1 600mm×100 mm×25 mm的常压辉光空气等离子体。等离子体发生器采用负高压针电极阵列与平板阳极结构,针电极的直径为1 mm,长度为20 mm,针电极之间的间隔为20 mm,针电极与平板零电位之间的距离为25mm,在每个负高压针电极末端周围同时形成圆锥形辉光放电,在平板地电极则形成大面积辉光放电。采用电压探针测量了该新型等离子体的放电特性,结果表明:放电脉冲的上升时间为26 ns,最高脉冲输出峰值电压为27 kV;利用该辉光等离子体对幅宽为1 000 mm聚四氟乙烯薄膜进行了表面改性处理,处理后其表面接触角由原来的124°降到69°,亲水性能大为提高。