Askin Altinoklu

Electromagnetic optimization of corrugated metallic sheets for maximum power focusing

We present full-wave electromagnetic optimization of corrugated metallic sheets to achieve maximum power focusing at desired locations when illuminated by plane waves. The corrugations are freely applied by moving the discretization nodes, leading to huge optimization spaces that are scanned by employing genetic algorithms. The required simulations are performed accurately and efficiently via the method of moments or the multilevel fast multipole algorithm. Hundreds of thousands of simulations are performed to demonstrate the feasibility of strong optical focusing, even with relatively small sheets in terms of wavelength. The corrugated sheets can be useful in various applications, such as energy harvesting, solar cells, imaging, and optical sensing.

Full-wave electromagnetic optimizations using surface integral equations and the multilevel fast multipole algorithm

We present an electromagnetic optimization environment based on full-wave solutions via surface integral equations and the multilevel fast multipole algorithm (MLFMA). Optimizations are performed by using genetic algorithms, while the required trials are performed accurately via MLFMA. The developed mechanism can handle many different operations, such as portion moving/removing, rotation, and gap opening, that have different effects in the constructed matrix equations but that can efficiently be executed in numerical simulations. The effectiveness of the optimization environment is demonstrated on alternative problems, such as the design of pixel antennas and corrugated sheets for optimal electromagnetic responses.

Full-wave electromagnetic optimizations of corrugated metallic sheets

We present optimizations of corrugated metallic sheets for desired electromagnetic responses. Patches of finite extents are considered and deformed to achieve the required characteristics. Optimizations are performed by using genetic algorithms (GAs), while the required accurate solutions are performed via the multilevel fast multipole algorithm. In addition to improvements in GAs, the optimization environment is enhanced by using dynamic accuracy control and adaptive mesh refinement to handle thousands of critical simulations per optimization. Numerical examples involving corrugated sheets that provide focusing abilities at desired locations are presented to demonstrate the capabilities of the developed optimization mechanism.

Full-Wave Electromagnetic Optimisation of Corrugated Metallic Reflectors Using a Multigrid Approach

A multigrid optimisation strategy is introduced to design passive metallic reflectors with corrugated shapes. The strategy is based on using genetic algorithms at multiple grids and shaping the metal sheets, starting from coarse details to fine tunings. This corresponds to a systematic expansion of the related optimisation space, which is explored more efficiently in comparison to a brute-force optimisation without using grid. By employing the multilevel fast multipole algorithm to analyse the electromagnetic problems corresponding to optimisation trials, we obtain accurately designed reflectors that provide focussing abilities with very high performances at single and multiple locations. The designed reflectors are also resistant to fabrication errors with less complex corrugations and simplified reflection mechanisms compared to those found by no-grid optimisation trials.

Publisher Correction: Full-Wave Electromagnetic Optimisation of Corrugated Metallic Reflectors Using a Multigrid Approach

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Efficient and Accurate Electromagnetic Analysis of Three-Dimensional Nano-Optical Structures

We present computational analysis of optical nanostructures, including but not limited to frequency-selective surfaces, metamaterials, nanoantennas, nanowires, and photonic crystals. A rigorous implementation based on surface integral equations and the multilevel fast multipole algorithm is developed for the analysis of such three-dimensional complex structures, without resorting to infinity, self-similarity, periodicity or homogeneity assumptions. The developed simulation environment provides accurate analysis of nanooptical structures to expand our knowledge on these important components of the state-of-the-art technology.

Shape optimizations of metallic sheets using a multigrid approach

We present a novel multigrid approach for the shape optimizations of corrugated metallic sheets by using genetic algorithms (GAs) and the multilevel fast multipole algorithm (MLFMA). The overall mechanism is obtained by an efficient integration of GAs and MLFMA, while the optimizations are improved by applying multiple grids at different layers. We show that the multigrid approach provides more effective optimizations than the conventional no-grid optimizations that employ the discretization nodes directly. The multigrid optimizations become useful especially as the problem size grows and no-grid optimizations demonstrate poor performances.

NUMERICAL CONSTRUCTIONS OF TESTING FUNCTIONS FOR IMPROVING THE ACCURACY OF MFIE AND CFIE IN MULTI-FREQUENCY APPLICATIONS

We present a new approach based on numerical constructions of testing functions for improving the accuracy of the magnetic-field integral equation (MFIE) and the combined-field integral equation (CFIE) with low-order discretizations. Considering numerical solutions, testing functions are designed by enforcing the compatibility of the MFIE systems with the accurate coefficients obtained by solving the electric-field integral equation (EFIE). We demonstrate the accuracy improvements on scattering problems, where the testing functions are designed at a single frequency and used in frequency ranges to benefit from the design procedure. The proposed approach is easy to implement by using existing codes, while it improves the accuracy of MFIE and CFIE without deteriorating the efficiency of iterative solutions.