Microwave broadband permittivity measurement with a multimode helical resonator for studying catalysts

The authors present a resonant permittivity measurement method which works over a large microwave frequency domain, with a very small volume sample of dielectric material. The cell is a helical resonator having many modes of resonance. The shifts of resonance frequency and Q-factors are better inter preted with a bilinear function which depends on the complex permittivity o f the material than by applying the classical perturbation formula. Results concerning two different catalysts which are used in the coupling oxidatio n methane reaction are given as a function of the temperature and the frequ ency to illustrate the correlation of both data sets and the differences in catalytic mechanisms.