Münster 1999 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 6: Poster

DF 6.3: Poster

Donnerstag, 25. März 1999, 09:30–12:30, Aula

Partially Filled Cylindrical Cavities:A Method to Measure Dielectric Properties at Microwave Frequencies. A Comparison of Perturbation Theory and Numerical Analysis with Experiments — •Marc Regier, Ulrich Erle, and Helmar Schubert — Universität Karlsruhe, Institut f"ur Lebensmittelverfahrenstechnik, Kaiserstr. 12, D-76128 Karlsruhe

Although nowadays microwave heating is used in nearly every home and also in industrial processes, these applications often are not optimized, due to the lack of knowledge of the exact electrical and magnetical fields. To solve the Maxwell’s equations assoziated to the problem (e.g. numerically) the dielectric properties (є′ + iє″) of the samples have to be known. Unfortunately, food samples are often mixtures with unknown dielectric constants. In order to examine heterogeneous samples without smooth surface, e.g. some kind of food, which cannot be characterized by a coaxial line reflectority probe, partially filled cavities are used. Well suited for samples with high dielectric constants is an H011 (=TE011) resonator with a small central filling, where the electrical field is almost zero. The regarded mode (H011) is - for an ideal cavity- degenerated with the E111 (=TM111)-mode, but this degeneration can be suppressed (at least partly) by distortions like preferential coupling or additional resonant or conducting volumes. To characterize the measuring system, the effects of such additional volumes and of first samples of load are studied by experiments and are compared with numerical calculations and perturbation theory.