Masaki Otomori

An acoustic metasurface design for wave motion conversion of longitudinal waves to transverse waves using topology optimization

This letter presents an acoustic metasurface that converts longitudinal acoustic waves into transverse elastic waves in an acoustic-elastic coupled system. Metasurface configurations are obtained by a level set-based topology optimization method, and we describe the mechanism that changes the direction of the wave motion. Numerical examples of 2D problems with prescribed frequencies of incident acoustic waves are provided, and transverse elastic wave amplitudes are maximized by manipulating the propagation of the acoustic waves. Frequency analysis reveals that each of the different metasurface designs obtained for different wavelengths of incident waves provides peak response at the target frequency.

Level Set-Based Topology Optimization for the Design of an Electromagnetic Cloak With Ferrite Material

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.

INVERSE DESIGN OF DIELECTRIC MATERIALS BY TOPOLOGY OPTIMIZATION

The capabilities and operation of electromagnetic devices can be dramatically enhanced if artiflcial 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 flnd 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 difierence between the efiective permittivity and a prescribed value. The optimization algorithm uses the adjoint variable method (AVM) for the sensitivity analysis and the flnite element method (FEM) for solving the equilibrium and adjoint equations, respectively. A Heaviside projection fllter is used to obtain clear optimized conflgurations. Several design problems show that clear optimized unit cell conflgurations 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 ofi-diagonal terms, and anisotropic material with loss. The results show that the optimized values are in agreement with theoretical bounds, conflrming that our method yields appropriate and useful solutions.

Level Set-Based Topology Optimization for the Design of Light-Trapping Structures

This paper discusses a systematic design method for light-trapping structures that can enhance the absorption capability of thin-film solar cells. Light-trapping techniques extend the length of the light path in the active layer and thereby enhance solar cell efficiency. The level set-based topology optimization method is constructed for the structural design of a light-scattering layer that is in contact with a cladding layer above the active layer. The optimization problem is formulated to maximize the light absorption coefficient of the solar cells. Numerical results demonstrate that the optimization can successfully find an appropriate configuration of the dielectric material and air for a light-scattering layer that enhances the light absorption coefficient at the desired wavelength.

Level Set-Based Topology Optimization for the Design of a Ferromagnetic Waveguide

This paper discusses a level set-based topology optimization method for the design of a ferromagnetic waveguide. The optimization problem is formulated to maximize the power of transmitted waves at prescribed frequencies. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of ferrite materials inside the waveguide. The results of the numerical examples for two different target frequencies show that the presented method successfully finds optimized configurations that maximize transmission power of waveguides for both forward and backward propagation.

Level Set-Based Robust Topology Design Considering Spatial Uncertainty

This study extends the authors’ proposed robust topology optimization approach to the design problems with two-dimensional nonuniform spatially-varied random parameters. The robust optimization is formulated to model the nonuniform spatial distribution of random variables by stochastic process model with a reduced set of random variables. The proposed approach integrates the robust optimization formulation and the level set-based topology optimization. The robust optimization is formulated to minimize the robust compliance that is defined as a weighted sum of the expected value and the standard deviation of mean compliance under volume constraint. Through numerical examples, the validity of the proposed robust topology optimization approach is demonstrated. Also, the eects that uncertain random parameters have upon the obtained robust optimum configurations are investigated through the power spectrum of the structural response.

Level set-based structural topology optimization of a metallic waveguide loaded with ferrite

This paper discusses a level set-based topology optimization method for the design of metallic waveguides loaded with ferrite inclusions. Ferrite materials can have frequency dependent permeability value due to the magnetic resonance phenomenon in a specific frequency range that can be altered by the magnitude of an external DC magnetic field. Thus, a rectangular waveguide loaded with periodic ferrite inserts can offer advantages in the tunability of operating frequencies and compactness. Here, the level set-based topology optimization incorporating a fictitious interface energy is used to find the configuration of ferrite materials in the waveguide that maximizes the transmission power of electromagnetic waves at prescribed frequencies. The objective function is formulated to maximize the transmission coefficient S21 at prescribed desirable frequencies. A numerical example is provided to examine the validity and utility of the presented method.