Hong Xiao

A Plasma Photonic Crystal With Tunable Lattice Constant

A tunable plasma photonic crystal (PPC) with a hexagonal structure is obtained by using a dielectric barrier discharge system with liquid electrodes. The lattice constant can be adjusted from 1.7 to 4.5 mm by changing the discharge parameters such as the applied voltage, the gas gap width, and the gas pressure. It results in the change of the dispersion relations of the PPCs.

Concentric-roll pattern in a dielectric barrier discharge in air

Concentric-roll pattern in a dielectric barrier discharge in air at pd value 29.3 hPa cm is observed in the presence of circular boundary and studied by an optical method for the first time. The weak correlation between microdischarges in concentric-roll patterns indicates that the concentric roll is a spatiotemporal chaos although the space integral of microdischarges is quasiperiodic in time. Spatiotemporal measurements of microdischarges suggest that the effective electric field near the boundary is weaker than that in the interior region. The bifurcation of concentric-roll patterns with the increase of voltage and selection of characteristic wavelength are also studied.

Temporal symmetry of individual filaments in different spatial symmetry filaments pattern in a dielectric barrier discharge

The temporal behavior of individual filament in different spatial symmetry filaments patterns in dielectric barrier discharge is investigated by using an optical method. A series of return maps of the discharge moments of individual filaments is given. It is found that the temporal symmetry of individual filament changes with the change of the spatial symmetry of filaments pattern as the applied voltage increases. The role of wall charges for this phenomenon is analyzed.

Emission Signal Analysis Based on Conventional and Modified Wavelet Cross-Correlation

Time-varying light emission signals, obtained in patterned dielectric barrier discharge, are processed by combining wavelet technique. For conventional one, it can be only presented the correlation trend between the two signals, while the modified correlation analysis can locate the correlated time exactly. Based on this, the probability density functions of correlation peak label number and correlation time can be measured. There are two, three, or four peaks in each discharge cluster mostly. It is found that Peak 1 at different space locations always occurs at the same time of falling edge of the applied voltage, while the other following ones occur dispersedly at rising edge of voltage.

Analysis of Competition between Patterns by Using Fast Fourier Transform

The Fast Fourier Transform is an important method in analysis patterns. In this paper, the FFT is used to the images of the patterns to analyze the competition of the modes and the evolution of the patterns. With the increase of applied voltage the competition between patterns are obtained in dielectric barrier discharge system with two liquid electrodes at the pressure p=0.3atm and p=0.2atm. The change of the modes and the Fourier spectral density reveal the process of the evolvement. It is found that the modes interact with each other and satisfy the three-wave resonance when the gas pressure is 0.3atm, so, the hexagonal superlattice pattern is observed in the discharge area. However, only one mode dominates in the spatial power spectrum when the gas pressure becomes lower to 0.2atm, so the square pattern dominates in the discharge area instead of the hexagonal superlattice pattern.

Analysis of the Pattern Evolution Based on Spatial Correlation and Fourier Spectra Technique

Images of patterns are processed with some image processing technology, such as binary image processing, space correlation function and Fourier transformation, thus some important intrinsic elements of active plasma and pattern formation can be presented more clearly. Images of random filaments, hexagonal, hexagonal superlattice pattern, and chaos state are obtained in dielectric barrier discharge system with increasing voltage. Using spatial correlation function, it is found that the average distance decreases with voltage increasing, and most hexagonal cells in both hexagonal and hexagonal superlattice pattern are relative perfect. For further investigation, these images are transformed to frequency domain and Fourier spectra are studied. It is found that the mode changes with voltage increasing. Both random filaments and chaos have single wavelength with all directions. The hexagonal pattern is formed with single-wavelength three-wave resonance, while hexagonal superlattice pattern is governed by three-wave resonance of two sets of modes. Keywordspattern evolution; spatial correlation function; Fourier spectra

Processing of Signals of Ring-Shaped Spots in Dielectric Barrier Discharge

Fast Fourier transform of the time series is an important way to analyze the periodic and chaos behavior of the signal. In this paper, the light signals of two types of ring-shaped spots, which are found in dielectric barrier discharge in the mixture of air and argon with two liquid electrodes, are recorded and compared through Fast Fourier transform. It can be seen from the Fast Fourier transform power spectra that, for the light signal of small ring-shaped spot, there still exists subharmonic frequency 1/2F and 1/4F, which is related to the periodic amplitude of the signal, besides the fundamental frequency F. However, for the large ring-shaped spot, the Fast Fourier transform power spectrum of light signal only has the basic frequency F, which reflects its temporal periodicity.

Study of the square grid pattern in dielectric barrier discharge by a CCD digital camera

Square grid pattern generated in a dielectric barrier discharge device is adopted by CCD digital camera. By using 2-D Fourier spectrum analyzing, it is found that the dot-line pattern is selected by two modes and the hexagonal pattern is selected by single mode, while the square grid pattern is formed by three wave resonance. For further investigation, the intensity distribution of square grid pattern is analyzed. Results show that the structures of square grid pattern is perfect and the intensity distribution along a line contains two types of intensity peaks, indicating that each cell of square grid pattern is composed of eight spots.

Analysis of the Transition from Hexagon to Square Pattern in Dielectric Barrier Discharge

Several spatiotemporal patterns: random spots, hexagon pattern, coexistences of hexagon and square pattern, and square pattern are obtained in dielectric barrier discharge system while increasing the voltage with other parameters fixed. By using image processing including spatial correlation function and Fourier spectrum, the structures of patterns and the bifurcation scenario are studied. It is shown that the structures of hexagon and square patterns are both perfect, and the spatial periodicity increases with the voltage increasing, whereas the mean distance between the neighboring filaments decreases. Moreover, the development of the modes excited from the system in this transition is investigated in detail. Both the two methods are in agreement with each other.