On the fabrication of durable dielectric-barrier discharge plasma actuators

Abstract

In the field of flow control, the application of plasma actuators as means to manipulate boundary-layer flows is subject to ongoing endeavors in research. Since dielectric-barrier discharge actuators simply consist of two electrodes separated by a dielectric, at first glance, their fabrication appears as straightforward procedure. However, it is mandatory to fulfill certain requirements related to durability and material degradation, reproducibility and geometrical properties. In particular, for a selected material combination the discharge characteristics of a plasma actuator need to be immune to its duration of operation. Therefore, this work revolves around the experimental investigation of different electrode and dielectric materials and recommends a possible actuator configuration. The analysis of the discharge properties is based on electrical signals (charge capacitor method) and snapshots of the plasma before, during and after operation. The tested dielectrics were Kapton, Plexiglas, quartz glass and ceramic (Al2O3). Furthermore, the discharge was excited at a plasma frequency of 11 kHz and peak-to-peak voltages of 8 to 12 kV. The exposed and encapsulated electrodes had a width of 2.5 and 10 mm, respectively. The tests were performed under quiescent-air conditions for a time span of 6 (for Kapton, Plexiglas and quartz glass) and 10 hours (for ceramic). The electrode materials applied to the Kapton, Plexiglas and quartz glass dielectric were either copper or conductive paint. Due to strong material degradation of Kapton, the actuator failed after less than 3 hours. For the conductive paint the conductivity of the electrode decreased, therefore, requiring larger power input over time. In order to meet higher durability and reproducibility requirements a screen-printing technique was used to manufacture the ceramic actuators. This method allows high precision of the electrode geometry and electrode thickness of less than 20 m, which is in the same order-of-magnitude compared to recent flow-control studies (materials: Mylar/copper, Polyethylenterephthalate/silver). As electrode materials, copper, silver/palladium (Ag-Pd) and silver/platinum (Ag-Pt) were tested. The ceramic actuators, in compliance with quartz glass, showed a very constant power consumption over the total duration of 10 hours. However, it turned out that the Ag-Pd and Ag-Pt actuators underwent changes of power consumption of +-5 %. The power consumption was continuously rising over the first half of the experiment and then decreasing to the end value after 10 hours. Such variation was not observed for the copper electrodes on the ceramic actuator. In turn, the power consumption was rising for about 3 hours before reaching the end value, undergoing variations of less than 3 %. The electrode composition likewise showed the best quality for the copper electrodes (after 10 hours of operation), while for the Ag-Pd and Ag-Pt electrodes a strong material degradation, manifesting as a reduction of the width of the exposed electrode and blackening of the latter, was observed. Overall, the initial running after reaching nearly constant discharge characteristics for the ceramic actuators was about 45 minutes. As the copper ceramic actuator turned out as a very promising material combination for a durable and reproducible configuration, it is planned to perform further tests of longer duration of operation with this actuator. In order to solidify the outcomes of this work, another experiment of simultaneous acquisition of electrical discharge properties and mechanical characteristics is scheduled.