504 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 36, NO. 2, APRIL 2008 Nanosecond-Pulsed Uniform Dielectric-Barrier Discharge Halim Ayan, Gregory Fridman, Alexander F. Gutsol, Victor N. Vasilets, Alexander Fridman, and Gary Friedman Abstract—The authors report a new nanosecond-pulsed dielectric-barrier discharge (DBD) for sterilization and other medical applications. In the literature, several discharges have been reported, with pulse durations on the order of hundreds of nanoseconds. In this paper, a novel pulsed DBD has been developed, with only few tens of nanosecond pulsewidths working uniformly over large range of electrode gap distance in air under atmospheric pressure. Index Terms—Nanosecond discharge, plasma medicine, uniform dielectric-barrier discharge (DBD). I. I NTRODUCTION F OR SOME period of time, the use of plasma in medicine has been limited to thermal discharges for cauterization and dissection [1]–[4]. Systems that employ afterglow from nonthermal plasma for medical treatment and disinfections have been proposed and demonstrated within the last decade [5], [6]. Although this makes it possible to work with living tissue and heat-sensitive surfaces, such treatment takes a rela- tively long time. It has been demonstrated recently that contact of living tissue with charges from nonthermal atmospheric- pressure plasma is much more effective for sterilization than plasma afterglow. However, nonuniform filamentary structure of usual nonthermal discharges like dielectric-barrier discharge (DBD) [7] in air and their sensitivity to gap nonuniformities pose significant challenges for medical and other applications. Filaments may produce highly localized heating and typically concentrate within areas where the gap is minimal. A novel nonthermal nanosecond-pulsed DBD in air is demonstrated here for the first time, which does not have filamentary structure and maintains uniformity over nonuni- form gap. The uniformity of this nanosecond-pulsed DBD is proven by using high-speed photosensitive film exposure. This nanosecond-pulsed DBD is also proven to be much more effective in killing bacteria on surfaces that are used as one of the DBD insulated electrodes than the conventional DBD. Manuscript received July 24, 2007; revised November 10, 2007. H. Ayan, A. F. Gutsol, V. N. Vasilets, and A. Fridman are with the De- partment of Mechanical Engineering and Mechanics, College of Engineering, Drexel University, Philadelphia, PA 19104 USA. G. Fridman is with the School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104 USA. G. Friedman is with the Department of Electrical and Computer Engineering, College of Engineering, Drexel University, Philadelphia, PA 19104 USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2008.917947 Fig. 1. Schematic of double spark-gap configuration external circuit. Rather than using expensive and often unreliable semicon- ductor devices for creating nanosecond pulses [8], [9], we have developed a relatively simple double spark-gap circuit for generation of pulses with durations around 10 ns. II. EXPERIMENTAL SETUP We have used sphere-to-plane discharge configuration of two DBD electrodes to demonstrate the new discharge. Dielectric- barrier-covered electrode was a glass test tube having approx- imately 5-mm radius of curvature and 0.75-mm thickness of glass with conductive silver paste filling inside. This test-tube electrode was in contact near its tip with the grounded plane metal electrode. An external circuit shown in Fig. 1 has been developed with a double spark-gap configuration to obtain short pulses. When the bigger (main) spark gap breaks down, charge that is initially stored in the main capacitor is transferred to the discharge as the voltage across the plasma electrodes rises rapidly. The smaller (secondary) spark gap starts to charge and eventually short outs the DBD, resulting in a rapid decay of the voltage across the DBD electrodes. Electrical analyses have been done by measuring instanta- neous current and voltage in the plasma gap using high-speed high-voltage probe (PVM-4, North Star High Voltage, AZ) and high-speed current probe (Model #4100, Pearson Electronics, CA). The data have been recorded by using high-speed oscillo- scope (TDS5052B, Tektronix, Inc., TX). A typical oscillogram of the discharge is shown in Fig. 2. The size of the main spark gap determines the voltage that appears across the discharge electrodes after the spark break- down. The fre‘uency of voltage pulses is determined by the magnitude of the current used to charge the main capacitor. Secondary spark gap affects mainly the length of the voltage pulse that is maintained across the DBD electrodes. For the 0093-3813/$25.00 © 2008 IEEE