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Birgitta Wäppling Raaholt*, Peter Ankarson, Henrik Toss

The dielectric properties of materials are commonly described for static conditions, either for a bulk geometry consisting of small particulates (e.g. stacked grains of a material) that facilitate the use of mixture formulae or for a state where the materials are ground and mixed into very small pieces or tiny particulates, e.g. crushed materials. However, many materials occur in in-flow processes and as larger particulates, e.g. spherically shaped objects. A cylindrical measurement cavity, with a centred co-cylindrical tube through the middle, was designed based on modelling and simulations, to enable accurate determination of dielectric properties under in-flow conditions. A model substance, mimicking silicon carbide foam (C-SiC foam) was studied, as well as so called water beads. The latter were spherically shaped, with diameter 13 mm and complex permittivity similar to water.

The in-flow configuration of the measurement cavity enables permittivity measurements in real time of a material that flows through the co-centric tube of the cavity, also for in-homogenous or particulate materials. Spherically shaped lossy and semi-lossy objects are used to demonstrate how the individual particulate, as well as the bulk dielectric properties in a microwave field, can be analysed by a model of effective complex permittivity. Such a model can describe the permittivity of such objects, stacked and surrounded by e.g. air.

Keywords: electromagnetic modelling; microwave; complex permittivity; dielectric properties; inhomogeneous loads; simulation; modelling; measurement

Proscience vol. 10

Pp 53-58

DOI: 10.14644/microwave25.010