1 Kyoto University, Kyoto, Japan, otomori.masaki.58r@st.kyoto-u.ac.jp 2 Technical University of D... more 1 Kyoto University, Kyoto, Japan, otomori.masaki.58r@st.kyoto-u.ac.jp 2 Technical University of Denmark, Lyngby, Denmark, jban@mek.dtu.dk 3 Technical University of Denmark, Lyngby, Denmark, sigmund@mek.dtu.dk 4 Kyoto University, Kyoto, Japan, takayuki@me.kyoto-u.ac.jp 5 Kyoto University, Kyoto, Japan, izui@me.kyoto-u.ac.jp 6 Kyoto University, Kyoto, Japan, shinji@prec.kyoto-u.ac.jp Abstract Composites with plasmonic inclusions, such as silver-dielectric composites, exhibit extreme properties that can dramatically enhance the capability and performance of optical devices, such as a superlens [1] and optical nanocircuits [2]. For the design of such plasmonic composites, Wallén et al. [3,4] numerically investigated periodic silver-dielectric composites that demonstrate an effective permittivity of −1, for the design of a near-field superlens and composites that have extreme anisotropy. However, their designs were limited to simple inclusions, such as those with a low volume fraction ci...
Physics and Simulation of Optoelectronic Devices XXII, 2014
ABSTRACT We propose a design methodology for systematic design of surface relief transmission gra... more ABSTRACT We propose a design methodology for systematic design of surface relief transmission gratings with optimized diffraction efficiency. The methodology is based on a gradient-based topology optimization formulation along with 2D frequency domain finite element simulations for TE and TM polarized plane waves. The goal of the optimization is to find a grating design that maximizes diffraction efficiency for the -1st transmission order when illuminated by unpolarized plane waves. Results indicate that a surface relief transmission grating can be designed with a diffraction efficiency of more than 40% in a broadband range going from the ultraviolet region, through the visible region and into the near-infrared region.
ABSTRACT We describe recent developments within nano-photonic systems design based on topology op... more ABSTRACT We describe recent developments within nano-photonic systems design based on topology optimization. Applications include linear and non-linear optical waveguides, slow-light waveguides, as well as all-dielectric cloaks that minimize scattering or back-scattering from hard obstacles.
Journal of Vibration and Acoustics-Transactions of the Asme, 2013
ABSTRACT Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves a... more ABSTRACT Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves are presented in this paper. Subwavelength cylindrical aluminum inclusions in air constitute the cloak design to aid practical realizations. The positions and radii of the subwavelength cylinders are determined by minimizing scattering from the cloak-structure and cylinder using the gradient-based topology optimization method. In the final optimization step, the radii of the subwavelength cylinders are constrained to three discrete values. A near-perfect narrow-banded and angular cloaking effect is obtained by optimizing for one target frequency. To get a larger bandwidth, the acoustic cloak is optimized for three frequencies at the cost of reduced peak cloaking performance at the center frequency.
ABSTRACT The capabilities and operation of electromagnetic devices can be dramatically enhanced i... more ABSTRACT The capabilities and operation of electromagnetic devices can be dramatically enhanced if artificial materials that provide certain prescribed properties can be designed and fabricated. This paper presents a systematic methodology for the design of dielectric materials with prescribed electric permittivity. A gradient-based topology optimization method is used to find the distribution of dielectric material for the unit cell of a periodic microstructure composed of one or two dielectric materials. The optimization problem is formulated as a problem to minimize the square of the difference between the effective permittivity and a prescribed value. The optimization algorithm uses the adjoint variable method (AVM) for the sensitivity analysis and the finite element method (FEM) for solving the equilibrium and adjoint equations, respectively. A Heaviside projection filter is used to obtain clear optimized configurations. Several design problems show that clear optimized unit cell configurations that provide the prescribed electric permittivity can be obtained for all the presented cases. These include the design of isotropic material, anisotropic material, anisotropic material with a non-zero off-diagonal terms, and anisotropic material with loss. The results show that the optimized values are in agreement with theoretical bounds, confirming that our method yields appropriate and useful solutions.
ABSTRACT We propose an inverse design methodology for systematic design of nanostructured surface... more ABSTRACT We propose an inverse design methodology for systematic design of nanostructured surfaces for color effects. The methodology is based on a 2D topology optimization formulation based on frequency-domain finite element simulations for E and/or H polarized waves. The goal of the optimization is to maximize color intensity in prescribed direction(s) for a prescribed color (RGB) vector. Results indicate that nanostructured surfaces with any desirable color vector can be generated; that complex structures can generate more intense colors than simple layerings; that angle independent colorings can be obtained at the cost of reduced intensity; and that performance and optimized surface topologies are relatively independent on light polarization.
ABSTRACT Fully enclosing, all-dielectric cloaks working for both Ez and Hz polarizations simultan... more ABSTRACT Fully enclosing, all-dielectric cloaks working for both Ez and Hz polarizations simultaneously are presented in this letter. The cloaks are effective for two antiparallel angles of incidence, and the layout of standard dielectric material in the cloak is determined by topology optimization. Scattering from cylinder and cloak is reduced for an Hz-polarized wave compared to an Ez-polarized wave by taking advantage of the surface mode at the perfectly electric conducting boundary. Perhaps contrary to simple intuition, fully enclosed, all-dielectric, low-contrast cloaks cannot be designed effectively when distributing a material with lower permittivity than the background material.
ABSTRACT This paper presents a structural optimization method for the design of an electromagneti... more ABSTRACT This paper presents a structural optimization method for the design of an electromagnetic cloak made of ferrite material. Ferrite materials exhibit a frequency-dependent degree of permeability, due to a magnetic resonance phenomenon that can be altered by changing the magnitude of an externally applied dc magnetic field. Thus, such ferrite cloaks have the potential to provide novel functions, such as on-off operation in response to on-off application of an external magnetic field. The optimization problems are formulated to minimize the norm of the scattering field from a cylindrical obstacle. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of the ferrite material. The numerical results demonstrate that the optimization successfully found an appropriate ferrite configuration that functions as an electromagnetic cloak.
1 Kyoto University, Kyoto, Japan, otomori.masaki.58r@st.kyoto-u.ac.jp 2 Technical University of D... more 1 Kyoto University, Kyoto, Japan, otomori.masaki.58r@st.kyoto-u.ac.jp 2 Technical University of Denmark, Lyngby, Denmark, jban@mek.dtu.dk 3 Technical University of Denmark, Lyngby, Denmark, sigmund@mek.dtu.dk 4 Kyoto University, Kyoto, Japan, takayuki@me.kyoto-u.ac.jp 5 Kyoto University, Kyoto, Japan, izui@me.kyoto-u.ac.jp 6 Kyoto University, Kyoto, Japan, shinji@prec.kyoto-u.ac.jp Abstract Composites with plasmonic inclusions, such as silver-dielectric composites, exhibit extreme properties that can dramatically enhance the capability and performance of optical devices, such as a superlens [1] and optical nanocircuits [2]. For the design of such plasmonic composites, Wallén et al. [3,4] numerically investigated periodic silver-dielectric composites that demonstrate an effective permittivity of −1, for the design of a near-field superlens and composites that have extreme anisotropy. However, their designs were limited to simple inclusions, such as those with a low volume fraction ci...
Physics and Simulation of Optoelectronic Devices XXII, 2014
ABSTRACT We propose a design methodology for systematic design of surface relief transmission gra... more ABSTRACT We propose a design methodology for systematic design of surface relief transmission gratings with optimized diffraction efficiency. The methodology is based on a gradient-based topology optimization formulation along with 2D frequency domain finite element simulations for TE and TM polarized plane waves. The goal of the optimization is to find a grating design that maximizes diffraction efficiency for the -1st transmission order when illuminated by unpolarized plane waves. Results indicate that a surface relief transmission grating can be designed with a diffraction efficiency of more than 40% in a broadband range going from the ultraviolet region, through the visible region and into the near-infrared region.
ABSTRACT We describe recent developments within nano-photonic systems design based on topology op... more ABSTRACT We describe recent developments within nano-photonic systems design based on topology optimization. Applications include linear and non-linear optical waveguides, slow-light waveguides, as well as all-dielectric cloaks that minimize scattering or back-scattering from hard obstacles.
Journal of Vibration and Acoustics-Transactions of the Asme, 2013
ABSTRACT Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves a... more ABSTRACT Directional acoustic cloaks that conceal an aluminum cylinder for airborne sound waves are presented in this paper. Subwavelength cylindrical aluminum inclusions in air constitute the cloak design to aid practical realizations. The positions and radii of the subwavelength cylinders are determined by minimizing scattering from the cloak-structure and cylinder using the gradient-based topology optimization method. In the final optimization step, the radii of the subwavelength cylinders are constrained to three discrete values. A near-perfect narrow-banded and angular cloaking effect is obtained by optimizing for one target frequency. To get a larger bandwidth, the acoustic cloak is optimized for three frequencies at the cost of reduced peak cloaking performance at the center frequency.
ABSTRACT The capabilities and operation of electromagnetic devices can be dramatically enhanced i... more ABSTRACT The capabilities and operation of electromagnetic devices can be dramatically enhanced if artificial materials that provide certain prescribed properties can be designed and fabricated. This paper presents a systematic methodology for the design of dielectric materials with prescribed electric permittivity. A gradient-based topology optimization method is used to find the distribution of dielectric material for the unit cell of a periodic microstructure composed of one or two dielectric materials. The optimization problem is formulated as a problem to minimize the square of the difference between the effective permittivity and a prescribed value. The optimization algorithm uses the adjoint variable method (AVM) for the sensitivity analysis and the finite element method (FEM) for solving the equilibrium and adjoint equations, respectively. A Heaviside projection filter is used to obtain clear optimized configurations. Several design problems show that clear optimized unit cell configurations that provide the prescribed electric permittivity can be obtained for all the presented cases. These include the design of isotropic material, anisotropic material, anisotropic material with a non-zero off-diagonal terms, and anisotropic material with loss. The results show that the optimized values are in agreement with theoretical bounds, confirming that our method yields appropriate and useful solutions.
ABSTRACT We propose an inverse design methodology for systematic design of nanostructured surface... more ABSTRACT We propose an inverse design methodology for systematic design of nanostructured surfaces for color effects. The methodology is based on a 2D topology optimization formulation based on frequency-domain finite element simulations for E and/or H polarized waves. The goal of the optimization is to maximize color intensity in prescribed direction(s) for a prescribed color (RGB) vector. Results indicate that nanostructured surfaces with any desirable color vector can be generated; that complex structures can generate more intense colors than simple layerings; that angle independent colorings can be obtained at the cost of reduced intensity; and that performance and optimized surface topologies are relatively independent on light polarization.
ABSTRACT Fully enclosing, all-dielectric cloaks working for both Ez and Hz polarizations simultan... more ABSTRACT Fully enclosing, all-dielectric cloaks working for both Ez and Hz polarizations simultaneously are presented in this letter. The cloaks are effective for two antiparallel angles of incidence, and the layout of standard dielectric material in the cloak is determined by topology optimization. Scattering from cylinder and cloak is reduced for an Hz-polarized wave compared to an Ez-polarized wave by taking advantage of the surface mode at the perfectly electric conducting boundary. Perhaps contrary to simple intuition, fully enclosed, all-dielectric, low-contrast cloaks cannot be designed effectively when distributing a material with lower permittivity than the background material.
ABSTRACT This paper presents a structural optimization method for the design of an electromagneti... more ABSTRACT This paper presents a structural optimization method for the design of an electromagnetic cloak made of ferrite material. Ferrite materials exhibit a frequency-dependent degree of permeability, due to a magnetic resonance phenomenon that can be altered by changing the magnitude of an externally applied dc magnetic field. Thus, such ferrite cloaks have the potential to provide novel functions, such as on-off operation in response to on-off application of an external magnetic field. The optimization problems are formulated to minimize the norm of the scattering field from a cylindrical obstacle. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of the ferrite material. The numerical results demonstrate that the optimization successfully found an appropriate ferrite configuration that functions as an electromagnetic cloak.
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Papers by Jacob Andkjær