Qiuyue Nie

Numerical studies of independent control of electron density and gas temperature via nonlinear coupling in dual-frequency atmospheric pressure dielectric barrier discharge plasmas

Dielectric barrier discharges (DBDs) provide a promising technology of generating non-equilibrium cold plasmas in atmospheric pressure gases. For both application-focused and fundamental studies, it is important to explore the strategy and the mechanism for enabling effective independent tuning of key plasma parameters in a DBD system. In this paper, we report numerical studies of effects of dual-frequency excitation on atmospheric DBDs, and modulation as well as separate tuning mechanism, with emphasis on dual-frequency coupling to the key plasma parameters and discharge evolution. With an appropriately applied low frequency to the original high frequency, the numerical calculation demonstrates that a strong nonlinear coupling between two frequencies governs the process of ionization and energy deposition into plasma, and thus raises the electron density significantly (e.g., three times in this case) in comparisons with a single frequency driven DBD system. Nevertheless, the gas temperature, which is mai...

Electron heating and mode transition in dual frequency atmospheric pressure argon dielectric barrier discharge

Plasma ionization, excitation, mode transitions and associated electron heating mechanisms in atmospheric pressure dielectric barrier discharges (DBD) driven by dual radio frequency sources are investigated in this paper. The electrons are found to be heated mainly by the high frequency component in the plasma bulk when discharged in α mode. On the contrary, the low frequency component is primarily responsible for heating in the sheath which is caused by intense motion in the sheath. It was also found that variation of the lower frequency component ratio could effectively modulate the electron energy distribution as determined from time averaged EEDF. The results above have demonstrated that the independent control of plasma parameters via non-linear synergistic effect between the dual frequency sources can be achieved through reasonable selection of processing parameters.Plasma ionization, excitation, mode transitions and associated electron heating mechanisms in atmospheric pressure dielectric barrier discharges (DBD) driven by dual radio frequency sources are investigated in this paper. The electrons are found to be heated mainly by the high frequency component in the plasma bulk when discharged in α mode. On the contrary, the low frequency component is primarily responsible for heating in the sheath which is caused by intense motion in the sheath. It was also found that variation of the lower frequency component ratio could effectively modulate the electron energy distribution as determined from time averaged EEDF. The results above have demonstrated that the independent control of plasma parameters via non-linear synergistic effect between the dual frequency sources can be achieved through reasonable selection of processing parameters.

Modeling and simulations on the propagation characteristics of electromagnetic waves in sub-atmospheric pressure plasma slab

Sub-atmospheric pressure plasma slabs exhibit the feature of relatively high plasma number density and high collisional frequency between electrons and neutral gases, as well as similar thickness to the electromagnetic (EM) wavelength in communication bands. The propagation characteristics of EM waves in sub-atmospheric pressure plasma slabs are attracting much attention of the researchers due to their applications in the plasma antenna, the blackout effect during reentry, wave energy injection in the plasma, etc. In this paper, a numerical model with a one-dimensional assumption has been established and therefore, it is used for the investigations of the propagation characteristics of the EM waves in plasma slabs. In this model, the EM waves propagating in both sub-wavelength plasma slabs and plasmas with thicker slabs can be studied simultaneously, which is superior to the model with geometrical optics approximation. The influence of EM wave frequencies and collisional frequencies on the amplitude of th...

Characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge with array generators

The two-dimensional spatially extended atmospheric plasma arrays by many parallel radio-frequency glow discharge plasma jets packed densely, represent a feature option of large-scale low-temperature atmospheric plasma technologies with distinct capability of directed delivery of reactive species and good insusceptibility to sample variations. However, it is still a challenge to form plasma jet with large area of uniform active species on a downstream substrate due to the complex interactions between individual jets. This paper proposes to numerically study the strategy and mechanism of control/modulation for the array discharge to produce two-dimensional plasma uniformity in the downstream working area. In this work, a two dimensional fluid model is employed to investigate the characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge (RF APGD) with array generators. The influences of upstream discharge characteristics, gas flow and their cooperative effects on the distribution of species densities, gas temperatures and the uniformity of active species in the material treating area is studied, and the essential strategy for the modulation method is acquired. The results will be significant for deep understanding of coupling behaviors of multiple plasma plumes in the RF APGD array and applications of the technology.

Ionization asymmetry effects on the properties modulation of atmospheric pressure dielectric barrier discharge sustained by tailored voltage waveforms

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath stru...

Study on the electromagnetic waves propagation characteristics in partially ionized plasma slabs

Propagation characteristics of electromagnetic (EM) waves in partially ionized plasma slabs are studied in this paper. Such features are significant to applications in plasma antennas, blackout of re-entry flying vehicles, wave energy injection to plasmas, and etc. We in this paper developed a theoretical model of EM wave propagation perpendicular to a plasma slab with a one-dimensional density inhomogeneity along propagation direction to investigate essential characteristics of EM wave propagation in nonuniform plasmas. Particularly, the EM wave propagation in sub-wavelength plasma slabs, where the geometric optics approximation fails, is studied and in comparison with thicker slabs where the geometric optics approximation applies. The influences of both plasma and collisional frequencies, as well as the width of the plasma slab, on the EM wave propagation characteristics are discussed. The results can help the further understanding of propagation behaviours of EM waves in nonuniform plasma, and applications of the interactions between EM waves and plasmas.

Research on radiation characteristics of dipole antenna modulation by sub-wavelength inhomogeneous plasma layer

The modulation and enhancement effect of sub-wavelength plasma structures on compact antennas exhibits obvious technological advantage and considerable progress. In order to extend the availability of this technology under complex and actual environment with inhomogeneous plasma structure, a numerical simulation analysis based on finite element method has been conducted in this paper. The modulation function of the antenna radiation with sub-wavelength plasma layer located at different positions was investigated, and the inhomogeneous plasma layer with multiple electron density distribution profiles were employed to explore the effect of plasma density distribution on the antenna radiation. It has been revealed that the optical near-field modulated distance and reduced plasma distribution are more beneficial to enhance the radiation. On the basis above, an application-focused research about communication through the plasma sheath surrounding a hypersonic vehicle has been carried out aiming at exploring an...

Experimental Studies on Radiation Intensification in Gigahertz Radio Frequency Band by Subwavelength Plasma Structures

Plasma-added intensification of radio frequency (RF) signals toward the future generation of compact antennas with wide-range requests has been studied experimentally in this paper. A technology based on modulation and enhancement effects of subwavelength plasma structures on application-focused RF electromagnetic radiation is developed. An inductively coupled plasma is applied to provide appropriate subwavelength structures, aiming at enhancing the electromagnetic radiation of an omnidirectional ellipse dipole antenna. The plasma mediated radiation enhancement on RF antenna signals of ~1 GHz is observed experimentally for the first time. It is shown that this technology is capable to obtain a significant gain up to nearly 10 dB higher than the free-space radiation without the plasma structure. And an enhanced frequency band of the typical GSM900 frequency range can be extended from 0.89 to 1.05 GHz. Meanwhile, electromagnetic signals transmitted by the plasma-added antenna still maintain good quality for communication. In addition, numerical simulations are also taken to reveal the mechanism of the radiation enhancement effects.