Inversion of multi-layer dielectrics using open-ended waveguides

Using various interactive optimization schemes, such as Levenberg-Marquardt and conjugate gradient, it was possible to invert multilayer media of up to nine layers with layer thicknesses of 0.05 lambda and a range of dielectric constants from 1.2 to 2.5. The model under study is a setup in which an open-ended waveguide ending in a flange is put is contact with the dielectric or plasma medium. The self-admittance of the waveguide describes the medium in terms of a set of parameters defining the unknown conductivity or permittivity profile. Choosing efficient optimization techniques, a search for these parameters is then carried out until the admittance of the trial medium agrees closely, within a certain tolerance, with the admittance of the actual medium. In order to check the robustness of the method, Gaussian noise was added to the exact values of the data simulating different dynamic ranges D/sup 2/. Results are given for a two-layer medium.<>