Ki Won Kim

Soonchunhyang University, Onyang, Chungcheongnam-do, South Korea

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Publications (40)41.03 Total impact

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    ABSTRACT: In this chapter, metamaterial perfect absorbers (MMPAs) are introduced by categories according to their operating frequencies: MMPA operating in the GHz, the THz, and the infrared (IR)/visible ranges. Although the existence of famous THz gap, below which the response of device is dominantly electronic, while above which it is dominantly photonic, the basic principle of operation of MMPA in the whole frequency range is nearly identical to each other, except for small details, for example, localized surface-plasmon polaritons which come into play in the IR/visible range because their energies correspond to IR/visible. Therefore, a simple scale down of the structure operating at GHz is possible for operating in higher-frequency ranges. For individual frequency ranges considered in this Chapter the broadband behavior, polarization independence, tunability and omni-directional behavior are discussed individually. In the near future MMPA will play a key role in the field of photonics and optoelectronics.
    No preview · Chapter · Jan 2016
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    ABSTRACT: Interests in asymmetric metamaterials (MMs) are increasing due to the existence of fascinating phenomena, such as high-quality-factor Fano resonance, analog of electromagnetically-induced transparency (EIT), slow light and chirality. However, there have been few researches studying the application of them to MM perfect absorbers. In this chapter, we discuss about the exploitation of EIT effect and the asymmetric resonators in achieving MM perfect absorbers. By considering the phase coupling between resonators, the EIT can be transformed into the electromagnetically-induced absorption, giving rise to an ultra-narrow and high quality-factor absorption. In addition, breaking the symmetry of resonators can induce multi-resonance that is suitable for developing multi-band or broadband absorption.
    No preview · Chapter · Jan 2016
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    ABSTRACT: With simple design and geometrical scalability, the investigated metamaterial (MM) absorbers might operate at higher or lower frequency with perfect absorption and be modified to reveal other capabilities relevant to the practical applications . The absorbers for GHz and MHz ranges are being developed to cover wider spectral regime, and to be independent of polarization and the incident angle of incident EM wave, which can be used in suppressing the radiation from mobile and other electric equipments. For MMs operating in the GHz and the lower-frequency ranges, another important challenging aspect should be overcome: the relatively (to the working wavelength) smaller size of the unit cell. The flexible MMPAs made by simpler fabrication processes come to be achieved. The present MMPAs also need simpler design, easier fabrication, lower production cost, and higher fabrication tolerance. Multi-band MMPAs using single pattern are interesting for the simple fabrication and the relevant advantages. Stealth science and technology based on microwave (L, X and Ku bands) MMPAs are going to be further developed. We feel confident that the MM revolution in the field of absorption has just started, and will present exciting new developments in the realm of practical applications in the coming years by overpassing the entry barrier and replacing the conventional applications using existing materials/structures, and by exploiting new ones. The industrial applications of MMs will be accelerated, which is the transition of MMs from basic and applied research into real world applications.
    No preview · Chapter · Jan 2016
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    ABSTRACT: The polarization of electromagnetic (EM) wave takes an important place in research of metamaterial perfect absorber (MMPA). In this chapter, we review the influence of the polarization of EM wave on MMPAs and, then, show polarization-independent MM absorbers by taking the advantage of structural symmetry. Even though the absorption is strongly reduced by increasing the incident angle of EM wave, to develop MM absorbers for the practical applications, we should use some special designs to reveal wide-incident-angle MMPAs . An analytical model is introduced by mean of the equivalent circuit in order to optimize the structure capable to work for larger incident angle. Finally, by introducing perfectly-matched-layer-like structure, MMPAs with wider incident angle and, at the same time, higher absorption can be achieved.
    No preview · Chapter · Jan 2016
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    ABSTRACT: Metamaterials (MMs) are artificial materials fabricated to have electromagnetic (EM) properties, which do not exist in nature. Among MMs, MM perfect absorbers (MMPAs) are promising candidates for the practical and rather immediate applications of MMs. In general, MMPA is 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, suppressing the reflection of incident 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. The third layer is a continuous metallic plate, blocking the remnant transmission. The properties of general MMPA are the absorption at specific frequency, the narrow absorption band and so on. Therefore, recently many researchers on MMPAs have focused on multi-band, broadband and tunable absorption. In this chapter, various researches so far about multi-band, broadband and tunable MMPAs are presented and reviewed.
    No preview · Chapter · Jan 2016
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    ABSTRACT: In this chapter, some theoretical aspects of propagation of electromagnetic (EM) waves in matters and their interaction with matters, which are essential to understand the phenomena occurring in metamaterial perfect absorber (MMPA) and to design and/or optimize the MMPA structures, will be presented. A brief introduction of broadband and resonant absorbers is provided. After a brief discussion on MMPA is given, the effective-medium approximation, which is essential for extracting various parameters from the simulated or the measured spectrum of MMPA, and its validity limit will be discussed. The equivalent-circuit theory and the transmission-line theory, will be briefly presented, and the introduction of several numerical techniques, such as finite-difference time-domain method, finite-element method and transfer-matrix method, will conclude this chapter.
    No preview · Chapter · Jan 2016
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    ABSTRACT: Perfect metamaterial absorber (PMA) can intercept electromagnetic wave harmful for body in Wi-Fi, cell phones and home appliances that we are daily using and provide stealth function that military fighter, tank and warship can avoid radar detection. We reported new concept of water droplet-based PMA absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very plentiful on the earth. If arranging water droplets with particular height and diameter on material surface through the wettability of material surface, meta-properties absorbing electromagnetic wave perfectly in GHz wide-band were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet-height and diameter- and apply to various flexible and/or transparent substrates such as plastic, glass and paper. In addition, this research examined how electromagnetic wave can be well absorbed in water droplets with low electrical conductivity unlike metal-based metamaterials inquiring highly electrical conductivity. Those results are judged to lead broad applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including transparent and bendable materials.
    Full-text · Article · Sep 2015 · Scientific Reports
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    ABSTRACT: We numerically and experimentally demonstrated a metamaterial perfect absorber (MPA) in MHz region based on a planar sandwiched metal-dielectric-metal structure. First, the single-peak perfect absorption was obtained at 400 MHz. The ratios of the periodicity of unit cells and the thickness to the absorption wavelength are 1/12 and 1/94, respectively. The advantage of structural design and the mechanism for the low-frequency MPA are described in detail by the comparison between calculation, simulation, and experiment. Influence of the incident angle of electromagnetic (EM) wave for both transverse-electric (TE) and transverse-magnetic (TM) polarization on absorption was also investigated, and the absorption was maintained to be above 95% at incident angles up to 30 ° . Finally, we propose a self-asymmetric structure, which induces the dual-band perfect absorption in the same range of frequency. The EM behavior of the excitation modes and the mechanism of the dual-band MPA are clearly explained. Especially, when two resonance modes are finely controlled to be close enough, the bandwidth (full width at half maximum) of MPA is enhanced to be nearly wider twice than that in case of single-peak perfect absorption. The enhanced bandwidth is still well preserved by varying the incident angle up to 30 ° for both TE and TM polarization. The results were also confirmed by both simulation and experiment. Our work is promising for potential practical applications in the radio range, such as radio-frequency shielding devices, single/dual-frequency filters, and switching devices.
    No preview · Article · Jun 2015 · Journal of Applied Physics
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    ABSTRACT: We propose polarization-independent and dual-broadband metamaterial absorbers at microwave frequencies. This is a periodic meta-atom array consisting of metal-dielectric-multilayer truncated cones. We demonstrate not only one broadband absorption from the fundamental magnetic resonances but additional broadband absorption in high-frequency range using the third-harmonic resonance, by both simulation and experiment. In simulation, the absorption was over 90% in 3.93–6.05 GHz, and 11.64–14.55 GHz. The corresponding experimental absorption bands over 90% were 3.88–6.08 GHz, 9.95–10.46 GHz and 11.86–13.84 GHz, respectively. The origin of absorption bands was elucidated. Furthermore, it is independent of polarization angle owing to the multilayered circular structures. The design is scalable to smaller size for the infrared and the visible ranges.
    Full-text · Article · Feb 2015 · Optics Express
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    ABSTRACT: We investigated the association between aging-induced apoptosis and cell proliferation in the anterior cruciate ligament (ACL) of aged patients.
    Preview · Article · Jan 2015 · The Journal of the Korean Orthopaedic Association
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    ABSTRACT: A small-size metamaterial perfect absorber operating at low frequency is proposed. Due to the special design, the unit-cell dimension with respect to wavelength is very small, a/λ ~ 1/17, at the absorption frequency of 377 MHz. The absorption frequency is strongly dependent on the length of zigzag wire. In addition, the absorption is more than 94% in a wide range of incident angle of electromagnetic wave up to 50°. The results show that the proposed absorber is promising to be applied into devices in radio region.
    Full-text · Article · Nov 2014 · Advances in Natural Sciences: Nanoscience and Nanotechnology
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    ABSTRACT: Objective We aimed to investigate the prevalence and psychosocial and neurophysiological correlates of depression in a large county-based cohort of Korean adults. Methods We recruited 2355 adults from a rural county-based health promotion program. The following psychometric scales were used: the Center for Epidemiologic Studies Depression scale (CES-D) was used to assess depression, the General Health Questionnaire (GHQ) was used to evaluate stress, and the Medical Outcome Study Social Support Survey (MOS-SSS) was used to determine perceived social support. Heart rate variability (HRV) was used to assess neurophysiological properties. The psychosocial and neurophysiological variables of adults with depression (CES-D score ≥25) and without depression (CES-D score <25) were statistically compared. A logistic regression model was constructed to identify factors independently associated with depression. Results We estimated that 17.7% of the subjects had depression, which was associated with old age, being female, being single, less religious affiliation, high education, low body mass index (BMI), low levels of aerobic exercise, low social support, and a low HRV triangular index. The explanatory factors of depression included high education, less religious affiliation, low levels of current aerobic exercise, low BMI, and low social support. Conclusion Given the relatively high prevalence of overall depression, subsyndromal depression should also be regarded as an important issue in screening. The independent factors associated with depression suggest that practical psychosocial intervention, including brief psychotherapy, aerobic exercise, and other self-help methods should be considered. In addition, the HRV results suggest that further depression screening accompanied by neurophysiological features would require fine methodological modifications with proactive efforts to prevent depressive symptoms.
    Full-text · Article · Oct 2014 · Psychiatry investigation
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    ABSTRACT: The effects of the electron mobilities and energy levels of different electron transport layer (ETL) materials on the performances were systemically investigated in blue phosphorescent organic light-emitting diodes. The spatial control of recombination zone (RZ) which was accompanied with triplet exciton quenching affected the balance between holes and electrons in the emission layer, resulting in the variations of the device performances. An optical micro-cavity effect in the electroluminescence (EL) spectrum around 500 nm was noticed by employing tris(8-hydroxyquinolinolato)aluminum (Alq(3)) ETL. This was attributed to the broadening of the emission zone through the emission layer over the ETL, exhibiting the greenish color coordinates. The current efficiency of the device with 3-phenyl-4(10-naphthyl)-5-phenyl-1,2,4-triazole (TAZ) ETL was much higher than that of the same structured device with any other ETL due to better charge balance as Well as the suppression of triplet exciton quenching by the narrow RZ with low electron mobility and proper band alignment.
    Preview · Article · Jun 2014
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    ABSTRACT: We propose a dual-band metamaterial perfect absorber at microwave frequencies. Using a planar metamaterial, which consists of periodic metallic donut-shape meta-atoms at the front separated from the metallic plane at the back by a dielectric layer, we demonstrate the multi-plasmonic high-frequency perfect absorptions induced by the third-harmonic as well as the fundamental magnetic resonances. The origin of the induced multi-plasmonic perfect absorption was elucidated. It was also found that the perfect absorptions at dual peaks are persistent with varying polarization.
    Full-text · Article · Dec 2013 · Optics Express
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    ABSTRACT: The classical electromagnetically-induced transparency (EIT)-like switching in metamaterials was experimentally demonstrated in the microwave-frequency region. The metameterial unit cell consists of two identical split-ring resonators, which are arranged on both sides of a dielectric substrate with 90°-rotation asymmetry. In our scheme, the classical EIT-like switching can be achieved by changing the polarization of the incident electromagnetic wave.
    Full-text · Article · May 2013 · Journal of Nonlinear Optical Physics & Materials
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    ABSTRACT: We propose multi-band metamaterial absorbers at microwave frequencies. The design, the analysis, the fabrication, and the measurement of the absorbers working in multiple bands are presented. The numerical simulations and the experiments in the microwave anechoic chamber were performed. The metamaterial absorbers consist of an delicate arrangement of donut-shape resonators with different sizes and a metallic background plane, separated by a dielectric. The near-perfect absorptions of dual, triple and quad peaks are persistent with polarization independence, and the effect of angle of incidence for both TE and TM modes was also elucidated. It was also found that the multiple-reflection theory was not suitable for explaining the absorption mechanism of our investigated structures. The results of this study are promising for the practical applications.
    Full-text · Article · Apr 2013 · Optics Express
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    ABSTRACT: Q fever is a zoonosis caused by a Coxiella burnetii. Q fever is clinically variable, presenting as asymptomatic infection, pneumonia, hepatitis and endocarditis. Treatment of acute Q fever with doxycycline is usually successful. Autoantibodies, such as anti-mitochondrial antibodies, smooth muscle antibodies (SMA), anti-cardiolipin and lupus anticoagulant, often rise in acute Q fever infection. Some cases may occasionally meet the criteria for autoimmune disease like systemic lupus erythematosus. We report a first case of Q fever that may mimic systemic lupus erythematosus in Korea.
    Preview · Article · Jan 2013
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    ABSTRACT: LiCoO2 thin films were fabricated by direct current magnetron sputtering method on STS304 and Ti substrates. The effects of substrate and annealing on their structural and electrochemical properties of LiCoO2 thin film cathode were studied. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction and field emission scanning electron microscopy. The as-deposited films on both substrates have amorphous structure. The (104) oriented perfect crystallization was obtained by annealing over 600 degrees C in STS304 substrate. The LiCoO2 thin film deposited on Ti substrate shows the (003) texture after annealing at 700 degrees C. The electrochemical properties were investigated by the cyclic voltammetry and charge-discharge measurement. The 600 degrees C-annealed LiCoO2 film deposited on STS304 substrate exhibits the inithial discharge capacity of 22 uAh/cm2 and the 96% capacity retention rate at 50th cycles. The electrochemical measurement on annealed films over 600 degrees C was impossible due to the formed TiO2 insulator layer using Ti substrate. As a result, it was found that the STS304 substrate seems to be more suitable material than the Ti substrate in fabricating LiCoO2 thin film cathode.
    No preview · Article · Jul 2012 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: We experimentally demonstrated a controllable electromagnetically induced transparency (EIT)-like spectral response at microwave frequencies in a planar metamaterial consisting of two identical split-ring resonators (SRRs) with side-by-side symmetry. In our scheme, phase coupling between the two SRRs (serving as the bright mode), which were excited strongly by the incident wave, was employed, and it was found that the EIT-like spectral response could be controlled by simply adjusting the incident angle. Thus, our scheme may be used for electromagnetic-wave switching. A high group index for slow-light application and a high quality factor could be obtained by simply controlling the incident angle.
    Full-text · Article · Apr 2012 · Journal of Applied Physics
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    ABSTRACT: A 30-year-old man was admitted to our hospital because of fatigue, palpitation and severe weakness of both legs. The admission laboratory findings revealed thyrotoxicosis, and 131I thyroid scintigraphic imaging revealed a low radioactive iodine uptake. He was treated for painless thyroiditis for about 4 months. However, thyrotoxic state had continued and radioactive iodine uptake was markedly increased in the follow up scan. Painless thyroiditis often relapses, but rarely develops into Graves' disease. This is a rare case in which painless thyroiditis was followed by Graves' disease.
    Preview · Article · Jan 2012

Publication Stats

210 Citations
41.03 Total Impact Points

Institutions

  • 2012-2013
    • Soonchunhyang University
      • College of Medicine
      Onyang, Chungcheongnam-do, South Korea
  • 2011
    • Catholic University of Korea
      Sŏul, Seoul, South Korea
  • 2001-2011
    • Gyeongsang National University
      • • School of Materials Science and Engineering
      • • Department of Biochemical Engineering
      Shinshū, Gyeongsangnam-do, South Korea