C1.3 - The Multipole Resonance Probe: From Simulation to Prototype

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
C1 - Wireless Sensors I
R. Storch, M. Lapke, J. Oberrath, C. Schulz, T. Styrnoll, P. Awakowicz, R. Brinkmann, T. Musch, T. Mussenbrock, I. Rolfes - Ruhr Universität Bochum (Germany), C. Zietz - Leibniz Universität Hannover, Garbsen (Germany)
376 - 380


Due to the dependencies of surface characteristics on the plasma parameters in coating processes it is obvious that supervising and controlling these parameters is inevitable. In this paper the development of a novel probe called “Multipole Resonance Probe” (MRP) is presented. The theoretical background to this concept relying on the well known plasma resonance spectroscopy is described in. This method enables the simultaneous determination of electron density ne, electron temperature Te and collision frequency ν by applying a fully symmetrical radio frequency signal into the plasma and measuring the absorption spectrum S(ω).
Verifying the analytical model is accomplished by 3D-electromagnetic field simulations. The complexity of the simulation model is increased step by step to separate different effects like perturbation by the feeding device that arises from basic conditions of realization. These simulation results are the basis for the layout of a multilayer printed circuit board. This PCB serves as a shielding device as well as a microstrip balun allowing an asymmetric feeding signal and thus making the driving circuit simpler. Two brass hemispheres are applied on the board acting as electrodes. To electrically separate them from the plasma the whole set up (PCB with hemispheres) is surrounded by a quartz-glass tube.
First measurements with this prototype are made and show very good compliance to analytical model and electromagnetic field simulations. The generation of the required radio frequency signal for feeding the probe as well as measuring the S11 parameter is done by a vector network analyzer. For industrial purpose a novel electronic system for signal generation and S11 measuring is needed. Therefore a symmetrical pulse generator with pulse widths of less than 100 ps has been developed. This pulse generator together with a sampling mixer form a subsampling unit that is driven by an ultra low phase noise timebase developed at the Ruhr University earlier. The unit for evaluating S11 as well as an improved version of the timebase is subject of current investigations.