Study Of The Evaluation On The Homogeneity Of Dielectric Barrier Discharges Basing On Digital Image Processing Technology

The homogeneous dielectric barrier discharges at atmospheric pressure could be of great interest for several industrial applications, such as surface modification, thin-film deposition, plasma sterilization, etc. Now it has become one of the main attention problems in the field of low temperature plasma. It has been carried out extensively study on how to achieve homogeneous DBD at atmospheric pressure. However, it still lacks in depth research on how to evaluate discharge uniformity quantitatively, in particular, the method is still relatively cumbersome and expensive. In this paper, we use two kinds of digital image processing technology which are simple and cheap to study this problem.A method was proposed to diagnose filamentary and homogeneous DBD qualitatively using two-dimensional spectral image obtained by image fourier transform technique, and a coefficient of spectrum amplitude fluctuationδwas also proposed to evaluate the homogeneity of a discharge quantitatively. The spectral image of filamentary DBD show a larger bright circle, which are far away from the center of the spectrum (DC component). However, The spectral image of homogeneous DBD show a smaller dark circle or ring, which are close to the center of the spectrum (DC component). Moreover, in a certain range, with an increase of the applied voltage, frequency or exposure time etc,δdecreases, the corresponding discharge intensity and homogeneity gradually increase.A method was first proposed to diagnose filamentary and homogeneous DBD quantitatively using gray distribution curve (GDC) obtained by image gray transformation technique, and a coefficient of gray variationσwas also proposed to evaluate the homogeneity of a discharge quantitatively. With an increase of the applied voltage, frequency or exposure time, the full-width at half-maximum (FWHM) of GDC increases and the amplitude of GDC reduces significantly in the case of filamentary mode, in contradistinction to the case of homogeneous mode, where its FWHM and amplitude keeps constant. The GDC shows that the minimum gray level is zero in the case of filamentary mode and can be any one in the case of homogeneous mode under different experimental conditions. Moreover, in a certain range, with an increase of the applied voltage, frequency or exposure time etc,σdecreases, the corresponding discharge intensity and homogeneity gradually increase.A preliminary exploration has been made on the research of the other characteristics of DBD using the image gray transformation technique. By comparing the characteristics of above two techniques on research in evaluating the uniformity of DBD, and studying on the characteristics of DBD under different pressure in air and argon, different gap distance in air at atmospheric pressure and different gas composition using the image gray transformation technique, the results show that the image gray transformation is one of a very effective method in studying the discharge characteristics of DBD.