# Ozone Generation by Surface Dielectric Barrier Discharge
## 3 Results and Discussion
### SDBD Plasma Imaging  
To observe the differences in the plasma morphology for three types of SDBD generators, we applied a time-resolved imagining technique. To this end, three characteristic 40 \(\upmu\)s time windows (A, B and C) were selected from the full cycle of the sinusoidal waveform and a series of fast-gated images was taken in each of those time windows. Time windows A and B were recorded at different times on the rising slope of the voltage waveform, during the streamer formation (the time delay between time windows A and B was \(\mathrm{t}_{\mathrm{AB}}=100\)\(\upmu\)s), and time window C (\(\mathrm{t}_{\mathrm{AC}}=650\)\(\upmu\)s) was recorded on the falling slope, during the regime of micro-glow discharge. The time position of those windows with respect to the voltage waveform is shown in Figure 2 (rectangle A). Figure 5 shows a set of typical plasma images captured in each time window for all three generators and a fixed applied voltage of \(\mathrm{V}_{\mathrm{pp}}=18.5\)\(\mathrm{k}\mathrm{V}\). In each image, the high-voltage electrode is located at the bottom, and the position of the smooth-edge and the serrated electrode is marked in the images with the dashed line (the position of the thin-wire electrode can be easily seen without marking it in the image). All the images are presented in the same pseudo-color scale representing the intensity of the plasma radiation.  
Plasma generated from the edge of the smooth-edge electrode at the positive-going half cycle of the voltage (time windows A and B) is characterized by the dense formation of positive streamers emerging at random locations along the entire length of the electrode and extending up to about 4 mm from its edge. Similarly, during the negative-going half cycle (C), micro-glow discharges are generated at random locations at the edge of the electrode. Those micro-glow discharges are of a lower intensity than the streamers and extend only about 2 mm from the electrode's edge. In the case of the serrated electrode, both the streamers and the micro-glow discharges develop primarily from the tips of the serrations, where the intensity of the electric field is the greatest. The length of the streamers emitted from the serrated electrode is similar to the ones generated from the smooth-edge electrode. However, while the micro-glow discharge emits more radiation at the tips of the serrated electrodes, the total plasma length is significantly shorter. In the case of the thin-wire electrode, streamers appear mainly during the first time window (A), while in time window B, only residual streamer radiation can be observed. Further, in the regime of micro-glow discharges (C), uniform radiation is emitted from around the wire, caused by the strong electric field forming around the wire due to its high curvature. The  
Figure 4: Discharge active power as a function of applied voltage for three types of generators.  
time-resolved images again confirmed that the thin-wire electrode inhibits the discharge formation. [PERSON] et al. [61] suggested that this behavior can be linked to the absence of irregularities at the surface of the thin wire, which suppresses the onset of the plasma streamers despite the high electric field.