Properties of Atmospheric Pressure Microdischarges in a Surface Dielectric Barrier Device

Dielectric barrier discharges (DBDs) are widely employed as cold plasma sources for plasma processing and applications [1]. The presence of an insulating layer interposed between electrodes prevents the formation of a diffuse plasma, inducing electrical discharges to assume the form of intermittent, fast and localized channels where current flows. In a Surface Dielectric Barrier Discharge (SDBD) device these microdischarges develop in a thin air layer just above the dielectric material surface. Besides other applications, this feature makes them interesting for the aerodynamics, being particularly suitable in order to energize the boundary layer of airflows surrounding objects [2]. As a matter of fact, many experimental studies have proved that SDBDs can generate an induced airflow of several m/s [3]. Here we present experimental results concerning the temporal and spatial structure of single microdischarges produced in a SDBD. Then a statistical analysis is performed for correlating our findings with the device operating conditions. In particular we have addressed the task of characterizing the differences between the two half-cycles of the applied sinusoidal voltage, since their contribution to the build up of the aerodynamic effects is a still unsettled question [2]. In order to investigate both the formation and propagation of the current channel we have collected emitted light with a fast photomultiplier. Spatial correlations and time delays have been measured between two or up to four different nearby positions. Differences in the duration and in the spatial elongation of the light emitting region have been detected during various phases of the discharge events and correlated with the operating conditions. Single microdischarge current signals have been measured with a fast current probe (100 MHz bandwidth) collected by a small portion of the electrode expressly sectioned. Differences in the amplitude, duration and transported charge associated to the microdischarges have been measured in correspondence of various phases of the discharge events. This is interesting because the boundary layer flow is influenced by collisions between neutral air molecules and charged particles moving in the discharge region.