Abstract-We present a new approach for inferring the electric field distribution inside materials in multimode cavities with mode stirrers. We calculate the electric field in the dielectric material by a two-dimensional modeling of a typical multimode microwave applicator with some mobile metallic sheets. We compare simulated results with classical approaches, such as Lambert's law or a constant electric field distribution. The proposed method allows for a better understanding of how these structures can be applied for heating materials when computing the microwave energy absorption in the dielectric. Finally, we perform experimental tests in a microwave multimode oven for validating purposes.

Abstract-In this paper, several mode-stirrer configurations are compared in order to establish their influence on the electric-field uniformity within an irradiated dielectric sample inserted in a microwave-heating applicator. Two different scenarios are evaluated with metallic sheets moving inside the multimode applicator. The different stirrer configurations are tested and compared for low-, medium-, and high-loss dielectric sample materials. Additionally, a straightforward procedure based on a generalized plane-wave approach is proposed and evaluated as a computationally efficient alternative for calculating the electric-field distribution inside materials processed in these microwave applicators with mode stirrers. Although very different electric patterns are achieved depending on stirrer geometry and sample permittivity, the plane-wave approach has been shown to provide a very good approximation for medium and high lossy dielectric materials.

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A novel inverse transmission-line method for the complex permittivity determination of arbitrary shaped materials is presented. Complex permittivity is inferred by using an inverse calculation procedure, which is based on a combined optimization strategy of both genetic algorithms and the gradient descent method. The optimization procedure matches the measured and simulated complex scattering parameters' frequency behavior of materials within a WR340 waveguide. High accuracy and practical suitability are validated through experimental tests. The dielectric properties of PTFE and epoxy resin mixed with iron-oxide-doped fiberglass have been measured for different shapes and positions. Dielectric multilayer structures have been used to demonstrate that this technique is able to measure the individual permittivity of each element of the structure. Both twoand three-dimensional approaches have been carried out and their advantages and drawbacks discussed.