Electrodynamic study of YIG filters and resonators.

Numerical solutions of coupled Maxwell and Landau-Lifshitz-Gilbert equations for a magnetized yttrium iron garnet (YIG) sphere acting as a one-stage filter are presented. The filter is analysed using finite-difference time-domain technique. Contrary to the state of the art, the study shows that the maximum electromagnetic power transmission through the YIG filter occurs at the frequency of the magnetic plasmon resonance with the effective permeability of the gyromagnetic medium µr ≈ -2, and not at a ferromagnetic resonance frequency. Such a new understanding of the YIG filter operation, makes it one of the most commonly used single-negative plasmonic metamaterials. The frequency of maximum transmission is also found to weakly depend on the size of the YIG sphere. An analytic electromagnetic analysis of resonances in a YIG sphere is performed for circularly polarized electromagnetic fields. The YIG sphere is situated in a free space and in a large spherical cavity. The study demonstrates that both volume resonances and magnetic plasmon resonances can be solutions of the same transcendental equations.

Hybrid finite-difference time-domain Fresnel modeling of microscopy imaging.

Full-wave electromagnetic analysis by the finite-difference time-domain (FDTD) method is combined with the scalar diffraction method to obtain a numerical tool for optical lens imaging. The FDTD method is applied to the modeling of scattering phenomenon in the vicinity of a target. Afterward, obtained results are coupled with the Fresnel diffraction method to project an image through the lens onto the image plane. The FDTD algorithm is able to provide the solution of the electromagnetic analysis of the target with all its geometrical complexity. It is also relatively effective, since it allows the arbitrarily shaped geometry of the target to be analyzed in a specified spectrum range with only one simulation run. Such coupled FDTD-Fresnel modeling exploits the advantages of both methods, maintaining the required accuracy and speeding up the overall computation of the image.

Properties of the FDTD method relevant to the analysis of microwave power problems.

The objective of the paper is to provide a systematic consideration and generalization of properties and features of the FDTD method in the context of its use in solving microwave power problems. This is aimed at filling the gap between the general theory of the FDTD method and the specific practice of its applications by microwave power engineers. The paper starts with a comparison of FDTD to other methods like FEM, from the perspective of microwave power simulations. It then discusses FDTD-specific models of lossy and dispersive media, conformal boundaries, field singularities, and modal excitation as well as error bounds due to numerical dispersion. Theoretical overview is illustrated with examples. References are provided to the literature where more details and application notes can be found.