Numerical simulation of electromagnetic radiation using high-order discontinuous galerkin time domain method

In this paper, we propose the simulation of 2-dimensional electromagnetic wave radiation using high-order discontinuous Galerkin time domain method to solve Maxwell's equations. The domains are discretized into unstructured straight-sided triangle elements that allow enhanced flexibility when dealing with complex geometries. The electric and magnetic fields are expanded into a high-order polynomial spectral approximation over each triangle element. The field conservation between the elements is enforced using central difference flux calculation at element interfaces. Perfectly matched layer (PML) boundary condition is used to absorb the waves that leave the domain. The comparison of numerical calculations is performed by the graphical displays and numerical data of radiation phenomenon and presented particularly with the results of the FDTD method. Finally, our simulations show that the proposed method can handle simulation of electromagnetic radiation with complex geometries easily

Design optimization of acoustic metamaterials and phononic crystals with a time domain method

A time-dependent adjoint approach for obtaining sensitivity derivatives for shape optimizations of acoustic metamaterials and phononic crystals is presented. The gradient-based design procedure is suitable for large numbers of design variables, and results are shown on achieving effective material properties with a unit cell and the broadband noise reduction with periodic arrays of cylinders. The acoustic wave propagation problem is solved in the time-domain using a Streamline Upwind/Petrov Galerkin formulation. Topology parameterization is accomplished using the homogenization method, and shape optimization is subsequently used afterwards to refine the geometries. Surface parameterization is accomplished using control grids, which are based on a Laplace equation. The combined strategy is compared with penalty-based topology optimization. Furthermore, the proposed topology optimization is also conducted on the design of a broadband acoustic cloaking device

Hybrid MIMD/SIMD High Order DGTD Solver for the Numerical Modeling of Light/Matter Interaction on the Nanoscale

This paper is concerned with the development of a scalable high order finite element type solver for the numerical modeling of light interaction with nanometer scale structures. From the mathematical modeling point of view, one has to deal with the differential system of Maxwell equations in the time domain, coupled to an appropriate differential model of the behavior of the underlying material (which can be a dielectric and/or a metal) at optical frequencies. For the numerical solution of the resulting system of differential equations, we have designed a high order DGTD (Discontinuous Galerkin Time-Domain) solver that has been adapted to hybrid MIMD/SIMD computing. Here we discuss about this later aspect and report on preliminary performance results on the Curie system of the PRACE research infrastructure

Time-dependent adjoint-based optimization of photonic crystals and metamaterials using a stabilized finite element method

In the current research, a time-dependent discrete adjoint algorithm for optimization of electromagnetic problems is developed. The proposed algorithm improves the efficiency for gradient-based optimization. The time-dependent Maxwell equations are discretized using a semi-discrete Petrov-Galerkin method, and time advancement is accomplished with an implicit, second-order backward differentiation formulation (BDF2). Utilizing the developed capability, two gradient-based shape design optimizations are conducted. In the first optimization an optical waveguide is designed with photonic crystals, and in the second an all-dielectric metamaterial is designed. A motivation for optimizing photonic crystals is due to their use as multi-band optical waveguides for telecommunication applications. For this design optimization, to ensure smooth surfaces, Bezier curves are employed to parametrically represent the shape. To reflect the design changes on the mesh, linear elasticity is used to adapt interior mesh points to boundary modifications. The cost function used in this design attempts to shift the band gap of the photonic crystals to desired frequency ranges. Results demonstrate a band gap shift from one single band gap to multiple band gaps is achievable. The motivation for optimizing broadband metamaterials is for their use as dielectric mirrors for applications where high power reflection is required. In this optimization, Hicks-Henne functions are utilized for shape parameterization and linear elasticity used once again for mesh adaptation. The cost function used attempts to widen the bandwidth of the metamaterial over a desired frequency range. Results demonstrate an increase of the full width at half maximum (FWHM) of reflection from 111THz to 303THz

Recent Trends in Computational Electromagnetics for Defence Applications

Innovations in material science, (nano) fabrication techniques, and availability of fast computers are rapidly changing the way we design and develop modern defence applications. When we want to reduce R&D and the related trial-and-error costs, virtual modelling and prototyping tools are valuable assets for design engineers. Some of the recent trends in computational electromagnetics are presented highlight the challenges and opportunities . Why researchers should equip themselves with the state-of-the-art tools with multiphysics and multiscale capabilities to design and develop modern defence applications are discussed

Integration of arbitrary lumped multiport circuit networks into the discontinuous galerkin time-domain analysis

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Efficient Large Scale Electromagnetics Simulations Using Dynamically Adapted Meshes with the Discontinuous Galerkin Method

A framework for performing dynamic mesh adaptation with the discontinuous Galerkin method (DGM) is presented. Adaptations include modifications of the local mesh step size (h-adaptation) and the local degree of the approximating polynomials (p-adaptation) as well as their combination. The computation of the approximation within locally adapted elements is based on projections between finite element spaces (FES), which are shown to preserve an upper limit of the electromagnetic energy. The formulation supports high level hanging nodes and applies precomputation of surface integrals for increasing computational efficiency. Error and smoothness estimates based on interface jumps are presented and applied to the fully hp-adaptive simulation of two examples in one-dimensional space. A full wave simulation of electromagnetic scattering form a radar reflector demonstrates the applicability to large scale problems in three-dimensional space.Comment: 33 pages, 8 figures, submitted to Journal of Computational and Applied Mathematic

Global optimization of metasurface designs using statistical learning methods

International audienceOptimization of the performance of flat optical components, also dubbed metasurfaces, is a crucial step towards their implementation in realistic optical systems. Yet, most of the design techniques, which rely on large parameter search to calculate the optical scattering response of elementary building blocks, do not account for near-field interactions that strongly influence the device performance.In this work, we exploit two advanced optimization techniques based on statistical learning and evolutionary strategies together with a fullwave high order Discontinuous Galerkin Time-Domain (DGTD) solver to optimize phase gradient metasurfaces. We first review the main features of these optimization techniques and then show that they can outperform most of the available designs proposed in the literature. Statistical learning is particularly interesting for optimizing complex problems containing several global minima/maxima. We then demonstrate optimal designs for GaN semiconductor phase gradient metasurfaces operating at visible wavelengths. Our numerical results reveal that rectangular and cylindrical nanopillar arrays can achieve more than respectively 88% and 85% of diffraction efficiency for TM polarization and both TM and TE polarization respectively, using only 150 fullwave simulations. To the best of our knowledge, this is the highest blazed diffraction efficiency reported so far at visible wavelength using such metasurface architectures