Impact of electrode design, supply voltage and interelectrode distance on safety aspects and characteristics of a medical DBD plasma source

In the frame of plasma source development for dermatological applications in the field of plasma medicine, operational safety of the devices is of superior priority. For sources based on the concept of dielectric barrier discharges (DBD), electric potentials with amplitudes in the range of some kV are arranged in close proximity to the skin of patients, wherein dielectric strength of the electrodes and leakage currents are crucial for electrical applicability. In this work, ceramic electrodes of 10 mm in diameter and varying ceramic thickness are operated at input powers up to 300 mW against non-biological counter electrodes. In a combined experimental and numerical approach, electric fields inside the ceramic are determined, whereas values are well below the dielectric strength of the material. The spectrally weighted plasma emission is within limit values of exposure to human skin as long as daily treatment does not exceeded 7 h. Neutral gas temperatures of up to 310 K are determined which underline the minor thermal impact of the plasma exposure. In contrast, values for reduced electric fields are of the order of some hundred Townsend and thus the electrons can initiate various secondary effects such as chemical reaction chains. Consequently, ozone concentrations in the discharges are quantified between 230 ppm and 1140 ppm in close proximity to the actual discharge volume and the results are discussed in the frame of risk assessment for therapeutic applications in dermatology