Determination of frequency response of complex permittivity by global optimization

conference paper

English

Abstract : This paper discusses the application of global optimization to find of the frequency dependence of the complex permittivity of dielectric materials. If a slice of a real unknown material inserted into waveguide, its reflection and transmission coefficients can be measured and used as the desired optimum for the optimization of its numerical model to find appropriate values of complex permittivity to yield the same behavior of the model like the unknown material exhibits during measurements. The described approach is practically used to simplify numerical EMC simulations of aircraft models containing parts from multilayer composite materials (a dielectric, laminate layer completed by a shielding formed by metallic grating). Due to the fine structure of the grating, the numerical model of the composite requires an extremely dense discretization mesh resulting in very high CPU-time and memory demands. When replacing composite parts by equivalent homogeneous dielectric parts with the same behavior in the electromagnetic field as the original multilayer structure, CPU-time and memory demands can be significantly reduced. To verify the concept of using the frequency dependent complex permittivity of equivalent model to replace real composite material, a three-dimensional model of a composite multilayer material situated in a hollow metallic waveguide R100 was created using the commercial FDTD solver CST Microwave Studio 2006b. This model served as reference instead of measurements results. To be able to perform hundreds of simulations necessary for the optimization, the optimized model was simplified to two dimensions in finite element COMSOL Multiphysics. Both in measurements and in modeling, frequency response of the reflection coefficient s11 and the transmission coefficient s21 were computed. The s11 and s21 were used to compose the objective function of the global optimization on four frequencies. The role of state variables changed by the optimization routine was played by the real part and the imaginary one of the complex permittivity. The COMSOL model of the structure was completed by MATLAB scripts implementing selected global optimization routines for computing frequency response of complex permittivity of the equivalent homogeneous layer. The described identification problem is solved by genetic algorithms (GA).

Microwave waveguide, composite, global optimization, Genetic Algorithm,

JILKOVÁ, J.; RAIDA, Z.

2008

13. 10. 2008

University of Damascus

Damascus, Sýrie

9954-8577-0-2

Mediterranean Microwave Symposium MMS'2008

1

179

182

4