Matthew Mishrikey

Efficient Procedures for the Optimization of Frequency Selective Surfaces

Eight different optimization algorithms are applied to determine the best configuration of a patch unit cell of a frequency selective surface used as a radar absorbing material. The algorithms include seven stochastic binary optimizers, which are based on the concept of genetic algorithms and evolutionary strategies as well as one quasi-deterministic optimizer based on an algorithm inspired by hill-climbing strategies. The comparison of results obtained from each algorithm shows the very high probability of finding global optima when a special microgenetic and a special quasi-deterministic algorithm is applied.

Analysis and optimization of frequency selective surfaces with inhomogeneous periodic substrates

A new type of metamaterial is proposed that may be considered as frequency selective surface (FSS), consisting of printed metal patches on inhomogeneous, periodic substrates. To analyze these structures a system of equations obtained from the Rigorous Coupled Wave Analysis (RCWA) is solved by the Method of Moments (MoM) with sub-domain rooftop basis functions and Galerkin testing functions. Several examples are outlined and analyzed using the MoM/RCWA technique. In order to validate the procedure, comparisons with a commercial time domain solver are performed. The introduced structures are designed using a micro-genetic algorithm in order to achieve artificial magnetic conductors (AMC) with optimum performance.

Improved performance of thin film broadband antireflective coatings

Antireflective coatings are useful for a range of applications, from minimizing the radar cross-section of stealth aircraft, to maximizing the efficiency of solar energy panels. New low-index nanorod thin films promise broadband, broad angle performance for such coatings. We demonstrate that a bandwidth increase from 38.5% to 113% is possible by using a simple evolutionary strategy to optimize the thin film material parameters. A two dimensional FDTD planewave periodic scattering approach is used to demonstrate additional performance increase by adding losses to a single layer. The same technique may be used for antireflective coatings for which no analytical solution exists, as is the case with dispersive, non-linear materials, special geometries, and coatings with metallic or ferromagnetic inclusions. A procedure is outlined for using the FDTD approach to obtain a map of reflection coefficients with respect to wavelength and incidence angle.

Efficiency of Various Stochastic Optimization Algorithms in High Frequency Electromagnetic Applications

We present the efficiency of various probabilistic algorithms, including the standard genetic algorithm, micro-genetic algorithm, evolutionary strategy, randomly initialized hill climbing, and mutation based algorithms for the optimization of electromagnetic devices operating at microwave and optical frequencies. Single fitness evaluations are costly because the electromagnetic field computation time is usually long. We therefore need to find strategies that provide optimal solutions in under a few hundred fitness evaluations. This constraint considerably affects the design of the optimizer. In order to obtain reliable guidelines, various optimization algorithms have been applied to three optimization problems.

Improved performance of numerical simulation algorithms for nanoscale electromagnetics

The optical response of nanostructures that exhibit pronounced plasmonic effects is studied and analyzed. Various approaches to solve light scattering problems in the time domain and in the frequency domain, using both the domain and the boundary discretization methods were used. Far-field and near-field characteristics of plasmonic nanostructures are investigated with several numerical algorithms to study the shape effect and the effects of the illumination angles on the resonance behavior. Numerical results with high accuracy, reduced complexity and reduced computational time due to extensive use of semi-analytical solutions are obtained. This set of numerical experiments demonstrates significant differences in the performances of different numerical methods. We observed that even simple geometries of plasmonic nanostructures may pose severe problems for various methods. We identify a strong need to select and modify numerical simulation algorithms according to the plasmonic effects, in addition to the standard selection of numerical method according to the geometrical settings and length scales.

Radiation Heat Transfer in Porous Materials

The effect of porosity on the radiation component of the thermal conductivity of the thermal barrier coatings is studied. Heat transfer in the disordered porous structures as well as the porous photonic bandgap structures is investigated. The pores, which size is comparable with the characteristic radiation wavelength λmax=2897.8/T μm, were found to be most efficient obstacles for the heat radiation.

High-Temperature Fiber Matrix Composites for Reduction of Radiation Heat Transfer

Recent progress in fabrication technology allows for the efficient control of electromagnetic waves by means of photonic devices. This could be attractive and promising also for hightemperature photonic structures to control electromagnetic heat transfer at temperatures above 1000 o C. We discuss the literature and present our own results on Fiber Matrix Composites (FMC), which could be superior to high-temperature metals or monolithic ceramics and can be designed for photonic applications. Possible applications include the protection of non-rotating components in high-temperature engines and turbines such as combustors and liners, coatings and parts for aerospace vehicles. Our discussion includes the material aspect and some relevant structure features. The use of woven fabrics to design new photonic band gap structures is discussed. An example of the use of the plane-wave expansion method for FMC design is given.

Positional Dependence of Mode Detection in FDTD based Photonic Crystal Simulations

We have developed an algorithm for evaluating the accuracy and reliability of photonic crystal simulations, and used this to analyze the influence of excitation and detector placement in FDTD simulations. We generate a map of locations where mode detection fails, and show that this is equivalent to a map of the node densities of the system. In addition to the expected high nodal densities at the symmetry points of the system, we find more difficult to characterize patterns of high nodal density for the higher order modes. Based on the observed behavior we are able to provide concrete suggestions for the optimal detection and excitation of modes in FDTD simulations of photonic crystal systems.