Patterned Dielectric Barrier Discharges for environmental and biomedical applications: From fundamentals to process control

• Applicant: Professor Dr. Julian Schulze, since 2/2023
• Subject Area: Microsystems ; Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432514770

Packed bed dielectric barrier low temperature plasmas operated at atmospheric pressure are frequently used for a variety of biomedical and environmental applications of high societal relevance such as the generation of reactive oxygen and nitrogen species (RONS), for e.g. wound healing, and exhaust gas cleaning, for e.g. the removal of Volatile Organic Compounds (VOCs) from gas streams. Such plasma sources have a complex design and typically contain a large number of dielectric/catalytic pellets in the plasma volume. Despite their enormous relevance for applications the fundamentals of their operation are unclear. In particular, the spatio-temporal electron dynamics that drives the plasma chemistry is not understood, since the electron dynamics in each consecutive period of the driving voltage waveform is different in such filamentary plasmas and no diagnostics that require averaging over multiple periods can be applied. Thus, applications are optimized empirically and, thus, inefficiently. Moreover, conventional packed bed DBDs suffer from an inherent pressure drop along the gas flow, because the pellets occupy most of the volume.In order to obtain a detailed fundamental understanding of such plasma sources, we developed a patterned DBD, where one of the electrodes is covered by a structured dielectric, e.g. semispheres embedded into a dielectric surface, and where no pellets in the volume are present, i.e. there is no pressure drop along the gas flow. Preliminary investigations show that this source design drastically improves the stability of the discharge, so that the spatio-temporal dynamics of energetic electrons are identical in consecutive periods of the driving voltage waveform. This allows using state-of-the-art diagnostics such as Phase Resolved Optical Emission Spectroscopy to reveal this dynamics. These preliminary studies have shown that the plasma is generated by a combination of three consecutive mechanisms, i.e. filamentary micro-discharges in the volume, which are generated at controllable positions, surface ionization waves, and surface microdischarges at the contact points of adjacent dielectric structures. In this project and based on a He/O2/N2 gas mixtures as well as rectangular driving voltage waveforms with adjustable duty cycle and on-times below 2 microseconds, we will study the spatio-temporal electron dynamics in such patterned DBDs systematically based on a synergistic combination of experiments and 2D fluid simulations. The electron dynamics, -density, and -temperature will be determined space and time resolved as a function of the driving voltage waveform, the gas mixture, the dielectric surface design and the catalyst loading, i.e. the shape of the dielectric structures, their size and material. Finally, the generation of RONS and VOC removal from gas streams will be investigated as a function of these control parameters and optimized based on scientific understanding rather than empirical methods.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Zaka ul Islam Mujahid, Ph.D., until 1/2023