Interaction between atmospheric pressure plasmas and non-planar dielectric surfaces in humid air dielectric barrier discharges

Abstract Dielectric barrier discharges (DBDs) have shown many advantages for surface treatments in various applications. In a common scenario, the surface to be treated is a dielectric that covers the electrode and acts as part of the discharge circuit, therefore surface properties such as permittivity, conductivity and morphology could affect the discharge dynamics. This remains an active research area. In the present study, systematic investigations are conducted on the discharge mechanism in humid air DBDs with one of the dielectric surfaces being non-planar, and the combined effects of surface morphology, voltage polarity and surface electrical properties are highlighted. A two-dimensional plasma hydrodynamics model was constructed and validated with experimental observations. The results showed that when the non-planar surface acts as the cathode a uniform surface discharge was apt to emerge, consequently leading to a higher and more uniform distribution of reactive species fluences towards the non-planar surface compared with the case when it acts as an anode. In cases with an uneven protrusion height, discharges were preferentially formed on the crests of higher protrusions and tended to inhibit the discharges on the adjacent lower ones. Additionally, the effects of the protrusion’s height and the permittivity and conductivity of the non-planar dielectric are discussed with focus on the discharge dynamics and fluences of reactive species towards the non-planar surface. Noting that the surfaces to be treated in reality are generally non-planar on the spatial scale of millimeters, for example human skin, or micrometers, such as unpolished dielectric surfaces, findings from the present work will contribute to an extended understanding of plasma–surface interactions from the perspective of both physics and applications.