A.V. Brovko - Ph. D. (Phys.-Math.), Associate Professor, Department of Applied Information Technologies, Yuri Gagarin State Technical University (Saratov). E-mail: brovkoav@gmail.com

The problem of leakage of microwave energy through the ports of the microwave heating conveyor type system is considered. Energy leakage leads on the one hand to the threat of health of personnel, and, on the other hand to a waste of energy. Therefore, the actual problem is the development of such a structure of the input and output ports of the system, which would not allow, or at least minimize, leakage of energy from the working chamber to the surroundings. A common drawback of known methods to solve this problem is that they can be used only in cases where the port aperture has a small size (up to 55 mm). In this case, the waveguide channel supports a small number of propagating modes at the operating frequency, and it becomes possible individual filtering of the modes. In the case when the port is larger (the size is subjected by of samples to microwave treatment (200-500 mm)), the number of modes in the channel becomes so great that their conventional filtration methods are not possible. In this paper, we propose the idea of using of metamaterials having a negative effective permittivity and permeability in the design of input and output ports of the conveyor belt system. Numerical experiments on the macro level shows that the waveguide walls formed with a layer of metamaterial of this type, do not transmit the eigenmodes, that is, the energy which leaks from the working chamber through a waveguide will be reflected back to the camera. For numerical analysis the FDTD method with the assignment of material properties using a Drude dispersion model has been used. Further, the article discusses the types of materials that can provide the required behavior (both negative values of effective permittivity and permeability). Among the possible options the system formed by a set of printed circuit boards with metallization in the form of splitted periodically spaced rings was chosen. This structure does not contain sharp metal edges, and therefore there is no danger of arcing effect in the presence of high-intensity electromagnetic fields. To determine the size of the structural elements of the metamaterial, providing the required characteristics, the FDTD simulation on micro level with direct modeling of the microstructure of the metamaterial is used in the paper. The parameters of structural elements that provide both negative values of effective permittivity and permeability and refractive index of the module close to 1 are determined using the numerical analysis. The paper also discusses the aspects of practical implementation of the input and output ports of the microwave heating conveyor type with walls formed by a layer of metamaterial of the considered types.

 

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