K. W. Kim

Metamaterial-based perfect absorbers

Metamaterials are artificially-engineered materials, possessing properties which are not readily observable in materials existing in nature. Since they show very novel properties such as left-handed behavior, negative refractive index, classical analog of electromagnetically-induced transparency, extraordinary transmission, negative Doppler effect, and so on, they can be used for perfect lens, invisibility cloaking, perfect absorption and transmission, etc. Metamaterial-based perfect absorbers (MMPAs) are promising candidates for the practical application of perfect absorbers. MMPA is usually composed of three layers. The first layer is periodically-arranged metallic patterns, whose structure and geometrical parameters should be carefully adjusted to fulfill the impedance-matching condition with the ambient, allowing no reflection of incident electromagnetic (EM) waves. The second layer is a dielectric layer, which allows a space for the EM waves to be dissipated, and sometimes plays a role of resonance cavity to prolong the time taken by the EM waves inside the second layer. Finally, the third layer is a continuous metallic plate, blocking remnant transmission. For practical usage, several aspects of MMPAs are to be considered seriously. Some of them are broadband operation, polarization-independent response, omni-directional response, and tunability. These aspects are basically determined by the structures of MMPA. Another important aspect is flexibility, which is determined by the material used in the fabrication. In this review, the basic operating principles of MMPAs and brief introduction of recent progresses in the field of MMPAs operating in different frequency ranges (GHz, THz and infrared/visible) are presented. Perspectives and future works for the investigation and the real application of MMPAs are also presented.

Perfect and broad absorption by the active control of electric resonance in metamaterial

Anti-oscillating plasmas have been the key to perfect absorption induced by magnetic resonance. This is an achievement in recent research on metamaterials (MMs), especially in GHz and the lower-frequency regions of electromagnetic waves. Here, a comprehensive view of perfect absorption is introduced by means of both magnetic resonance and electric resonance in meta molecules. A conventional metal-dielectric-metal MM absorber is proposed to obtain dual-band perfect absorption. It is clarified that the mechanism of dual-band absorption is due to fundamental (at 7.2 GHz) and third-order (at 18.7 GHz) magnetic resonances. Finally, we develop triple-band absorption by integrating resistors in to the MM absorber. The electric resonance, under the presence of resistors, matches the impedance of the MM absorber with the air at 13 GHz and gives rise to the new absorption band, with absorption higher than 90%.

Comprehensive Studies on the Magnetic Reversal Properties of Bilayered Magnetic Anti-Dot Lattices

In this work, we report the results of our study on the magnetization-reversal properties in a bilayered magnetic antidot lattice (BMAL) system consisting of upper perforated thick Co layer of 40 nm and lower continuous thin Ni layer of 5 nm, probed by using a superconducting-quantum-interference-device (SQUID) magnetometer and by magnetic-force microscopy (MFM). Such a BMAL structure was fabricated by using photolithography and controlled wet-etching processes. A systematic study on the in-plane anisotropy, and the switching-field properties was carried out. The atomic-force-microscopy (AFM) image clearly indicated that the anti-dot array structures are well defined, and the local element composition was confirmed by using the energy dispersive spectra (EDS). The room-temperature hysteresis curves, taken along different directions of the applied magnetic-field, were proved to be useful to understand the magnetic anisotropy in the sample. A kind of uniaxial anisotropy with easy axis along 0° and hard axis along 90° of applied field direction was observed. To get a comprehensive knowledge about the domain configuration, we performed the MFM imaging along the easy and hard axis of the lattice. The MFM images revealed well-defined periodic domain networks which can be ascribed to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The observed changes in the magnetic properties are closely related to the patterning that pins the domains as well as to the magneto-anisotropic BMAL structure.

Switching and extension of transmission response, based on bending metamaterials

The electromagnetically-induced transparency (EIT)-like effects in planar and non-planar metamaterials (MMs) were investigated for microwave (GHz) frequencies. The specific MMs used in this study consisted of a cut-wire resonator and a ring resonator, where were placed on the top and the bottom layers, respectively. A transmission window was produced, due to the interference between bright- and bright-mode coupling. Using the numerical and the experimental results, we demonstrate that the bending of MM leads to enhanced transmission and bandwidth, as well as an additional EIT-like peak. This provides an effective way of realizing the tunable devices, including the switching sensors.

Physical properties of Ni/sub 2/MnGe alloy films with different degrees of atomic orders

Ni/sub 2/MnGe alloy films were fabricated by flash-evaporation. A wide substrate temperature range (from 150 to 730 K) was chosen to prepare the alloy films with significantly different atomic orders. Various physical properties, including the magnetic, the optical, and the magnetooptical properties, were investigated. It was shown that the Ni/sub 2/MnGe alloy film with an L2/sub 1/-type structural order has been successfully fabricated. The ordered films exhibit the physical properties close to the corresponding bulk alloy. Unexpectedly, the disordered alloy films are not ferromagnetically ordered. These results were further analyzed in connection with the electronic structures of the alloy.

Antibacterial Activity and other Functions of Codium fragile and Chaenomeles sinensis Extracts by Extraction Method

We have extracted Codium fragile in two ways : hot water extraction and alcohol extraction. We also have extracted dried fruit of chinese quince (Chaenomeles sinensis) with hot water. Antimicrobial activities of Codium fragile and Chaenomeles sinensis extracts were investigated using paper disc method and continuous sequential dilution method respectively. Total phenol and flavonoid contents were also measured. As a result, alcohol extracts of Codium fragile showed high antimicrobial activity and did not affect beneficial intestinal microorganisms. In addition, hot water extracts of Chaenomeles sinensis showed antimicrobial activity. These results suggest that alcohol extracts of Codium fragile and hot water extracts of Chaenomeles sinensis can be used as antimicrobial agents in various aspects. In addition, they exhibit high phenol content and are considered useful as functional materials.

Biosynthesis of novel daidzein derivatives using Bacillus amyloliquefaciens whole cells

Abstract Biotransformation of daidzein was performed by using Bacillus amyloliquefaciens KCTC 13588, Lactococcus lactis subsp. lactis KCTC 3769, Leuconostoc citreum KCTC 13186, Kluyveromyces lactis var. lactis KCTC 17704, Pediococcus pentosaceus KCTC 3116, and Lactobacillus sakei KCTC 13416 cells as a biocatalyst. Four derivatives of daidzein such as daidzein-7-O-phosphate, daidzein-7-O-β-D-glucoside, daidzein-7-O-β-(6′′-O-succinyl)-D-glucoside, and 4′-Ethoxy-daidzein-7-O-β-(6′′-O-succinyl)-D-glucoside were isolated from the biotransformation reaction mixture. The structures of the molecules were elucidated by HPLC, HR-QTOF-ESI/MS and 1H-NMR analyses. Among them 4′-Ethoxy-daidzein-7-O-β-(6′′-O-succinyl)-D-glucoside derivative is novel compound and not reported elsewhere till now.

Physical properties of Ni/sub 2/MnGe alloy films with different atomic orders

Ni/sub 2/MnGe films with significantly different structural orders were fabricated, and the influence of atomic ordering on various physical properties has been investigated. The structural characterization was performed by X-ray diffraction (XRD). The temperature dependence of magnetization was investigated with a superconducting quantum interference device. The optical properties were obtained using a spectroscopic ellipsometer, and the magneto-optical properties were understood by measuring the equatorial Kerr effect (EKE). Infrared and ultraviolet spectra of the films were also studied. It was found that the structural disorder in Ni/sub 2/MnGe film causes lack of the ferromagnetic order and noticeable changes in the energy band structure.