Development of a smart positioning sensor for the plasma needle

In the study of plasma¿surface interactions, a well-defined distance from thesurface is desired. In this paper, an innovative method is proposed for usingthe intrinsic properties of a low-power atmospheric plasma to control thisdistance. It is proposed that the vicinity of a (even poorly) conductingsurface imposes a change in the plasma impedance. This effects thereflection of electrical power, which can easily be measured, and provides anon-contact sensor for the distance between the plasma source and thesubstrate. For this sensor to work, a low-loss and efficient matching networkis designed, such that changes in the reflected power are relatively high.With this high-quality matching network at hand, a characterization of theplasma needle is performed in terms of impedance and related parameters.Although characterization is not essential for the development of the sensor,it contributes to fundamental knowledge about the plasma source. Finally,coherence measurements are performed to determine the performance of theabove described sensor in different experimental settings.