A Minimally Invasive Monitoring Concept for Plasma-Assisted Surface Treatments in PET Bottles

This paper presents a novel approach to plasma monitoring in the context of plasma-assisted surface treatments in PET bottles. In industrial state-of-the-art production of PET-based beverage bottles, a so-called Plasmaline antenna is inserted into the bottle which provides both process gases and microwave excitation to generate the plasma state required for coating or sterilization on its inside. The proposed concept based on the planar multipole resonance probe (pMRP) allows for a non-invasive supervision of the plasma from the outside of the bottle wall. Since plasma and probe head are only separated by dielectric materials in between, the sensor's electric field is able to interact with the plasma and the resonance behavior that occurs can be evaluated and tracked. The performance of the concept regarding changes of the plasma electron frequency and the electron collision frequency are investigated within 3D full-wave simulations in CST Microwave Studio. Measurements of an argon plasma are presented as a proof-of-concept, with the plasma being monitored from the plasma-remote side of a PET bottle section.