Ilsung Seo

Meta-lens design with low permittivity dielectric materials through smart transformation optics

We report here a design method based on smart transformation optics (STO) to control the range of the permittivity values of the materials required to manufacture transformation optics devices. In particular, we show that it is possible to reduce the maximum electric permittivity value required to realize a STO device with certain functionality by means of a simple conceptual elastic stretching process. We illustrate the design procedure with two types of collimator meta-lens designs, which we call warping space collimator meta-lens and half fisheye collimator meta-lens, respectively. We provide design examples of these two types of lenses with the help of COMSOL Multiphysics software. These two design examples are fabricated with commonly available dielectric materials by means of 3D printing technology. For the functional verification of these two collimator lenses, we provide measurement results obtained with transverse electric waves of frequency range 7–13GHz.

Quasi-conformal transformation optics with elasto-electromagnetic metamaterials: Design algorithm

We report here a design method that is used to determine the initial shapes of elasto-electromagnetic metamaterial blocks with respect to the given shape of a hiding object when these blocks are applied to the problem of carpet cloaking. Starting from the inhomogeneous permittivity distribution of a cloak, derived using transformation optics, we use an inverse process to design the initial shape of a uniform permittivity material for an arbitrary value of Poissons ratio in the range from −1 to 0.5. Then, by elastic compression of the initially uniform metamaterial, we obtain the inhomogeneous permittivity distribution that is required for cloaking. Our design method is then experimentally verified by measurements of the electric field profiles in smart metamaterial cloaks.

Two-dimensional dielectric collimator design and its experimental verification for microwave beam focusing

A collimator is an electromagnetic device that focuses or aligns the direction of wave propagation to achieve a narrow, intense beam. In this study, we propose a two-dimensional dielectric collimator for microwave beam focusing. This is something that is difficult to achieve using theoretical- or intuition-based approaches. We therefore used a systematic design process, which is referred to as the phase field design method, to obtain an optimal topological configuration for the collimator. The phase field parameter determines the optimal configuration of the dielectric material and, as a consequence, it determines the relative permittivity of the component. To verify the design results, we fabricated a prototype via three-dimensional printing and performed an experimental verification using an electric field scanner to measure the near field distributions of the designed collimator positioned parallel to an incident wave. We also performed angle dependent experiments for which the collimator position was ...

Design method for broadband free-space electromagnetic cloak based on isotropic material for size reduction and enhanced invisibility

A design method is proposed that not only improves the invisibility of but also minimizes the size of a two-dimensional (2D) free-space electromagnetic cloak based on the quasi-conformal mapping (QCM) technique. The refractive index profile of the cloak based on the QCM is optimally scaled to minimize performance deterioration due to the imperfect isotropy of the cloak medium. Moreover, the method can be applied to compensate for the performance degradation due to size reduction. Based on the proposed method, as much as a 78.3% reduction in size is demonstrated. Enhancement of invisibility is evidenced by a 71% reduction in the normalized scattering cross section (SCS) at 10 GHz. Performance enhancement and miniaturization are achieved simultaneously with the extremely simple proposed method, making it one of the most practical cloaks reported thus far. Finally, experimental results over a broad bandwidth as well as for a wide range of incident angles are provided for cloaks fabricated using a 3D printer, which validate the effectiveness of the proposed method of cloak design.

All-dielectric structure development for electromagnetic wave shielding using a systematic design approach

Common dielectric metamaterials for electromagnetic (EM) interference shielding, stealth applications, and EM cloaking generally require larger thicknesses than the wavelength of incidence light. We propose an all-dielectric metamaterial inspired structure using a systematic approach based on the phase field design method. The structure is composed of periodically arranged unit structures that have a 2D configuration, which is sub-wavelength thick over its entire structure. The proposed structure provides anomalous reflections to prevent reflections back toward the wave source and is anti-penetrative over the microwave band with no conductive materials. We digitally fabricated the designed structure using 3D printing and verified the design specifications by experiments.

Design of a wideband polarisation-independent metamaterial with arbitrary relative permittivity based on the dielectric mixing theory

We propose a design method for a wideband polarisation-independent metamaterial structure by randomly mixing dielectrics. The relative permittivity (or refractive index) of the metamaterial can be varied by the volume fraction of the mixed dielectric media. The required volume fraction can be estimated by the conventional mixing formula. The designed metamaterial can be easily fabricated with a conventional 3D printer. Measurement of the relative permittivity of the proposed medium is also performed, which shows that the proposed metamaterial has polarisation independence and operates in a wide frequency band.

Broadband polarisation-independent metamaterial based on modified ELC structure

A broadband polarisation-independent metamaterial is proposed by combining modified electric-LC (ELC) metamaterials that are orthogonally aligned with each other and metal coated by via hole. Using electrically induced current along a metal patch, the broadband permittivity which is always greater than that of the substrate is determined. The maximum permittivity, which is about 25% higher than that of the substrate, is confirmed. The proposed metamaterial is verified by full-wave simulations and experiments for six differently polarised incident waves and frequencies from 6 GHz to 10 GHz.

Experimental verification of ground-plane cloak composed of random pattern unit-cell fabricated by 3D printer

A ground-plane cloak is fabricated by a 3D printer, whose unit-cell has a random pattern. The performance of the cloak is experimentally verified.

Design method for compensating lateral beam shift of ground-plane cloak

This paper demonstrates a method to improve the accuracy of the ground-plane cloak by compensating for the lateral beam shift. The lateral beam shift can be compensated by increasing the height of the bump with the upper boundary of the cloak and shifting the reference ground plane downwards in the cloaking region. Moreover, the asymmetric ground-plane cloak, which represents not only the lateral beam shift but also an error of the reflection angle, is also compensated by generating the initial grids unequally. The accuracy of the proposed method is verified via ray tracing simulation.

Efficient calculation method of electromagnetic scattering by finite I-shaped metamaterial rectangular plate

The calculation method of the scattering by a finite metamaterial rectangular plate is proposed. The surface current distributions are modeled for a transverse electric(TE) and transverse magnetic(TM) waves. The proposed method is numerically and experimentally verified by comparing the Radar Cross Section(RCS).