• Journal of Powder Materials
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• v.23 no.1
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• pp.38-42
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• 2016

$BaTiO_3$-coated Fe nanofibers are synthesized via a three-step process. ${\alpha}-Fe_2O_3$ nanofibers with an average diameter of approximately 200 nm are first prepared using an electrospinning process followed by a calcination step. The $BaTiO_3$ coating layer on the nanofiber is formed by a sol-gel process, and a thermal reduction process is then applied to the core-shell nanofiber to selectively reduce the ${\alpha}-Fe_2O_3$ to Fe. The thickness of the $BaTiO_3$ shell is controlled by varying the reaction time. To evaluate the electromagnetic (EM) wave-absorbing abilities of the $BaTiO_3@Fe$ nanofiber, epoxy-based composites containing the nanofibers are fabricated. The composites show excellent EM wave absorption properties where the power loss increases to the high frequency region without any degradation. Our results demonstrate that the $BaTiO_3@Fe$ nanofibers obtained in this work are attractive candidates for electromagnetic wave absorption applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.10 s.89
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• pp.969-976
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• 2004

The wide and growing use of cellular phones has raised the question about the possible health risks associated with radio-frequency electromagnetic fields. It would be helpful for phone users to blow the exposure levels during cellular phone use. But it is very difficult to recognize the amount of exposure, because measuring accurate level of RF is a difficult matter. In this study, we developed a model to estimate the exposure level and the individual risk of exposure by utilizing the available informations that we can get. We used such parameters as usage time a day, total using period, distance between cellular phone and head, slope of cellular phone, hands-free usage, antenna pulled out or not SAR(Specific Absorption Rate) of cellular phone, and flip or folder type. We proposed a model presenting individual risk of RF exposure from level 0 to 10 by using a neural network.

• Polymer(Korea)
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• v.33 no.1
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• pp.91-95
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• 2009

We fabricated the electromagnetic (EM) noise absorber films for high temperature use by blending a soft magnetic powder with poly(amide imide) (PAI). The EM noise absorber films of PAI/soft magnet composite were prepared by casting the solution of poly(amide amic acid)/soft magnet powder into glass substrate with casting applicator device and then thermal imidization. The obtained films were fully characterized and their physical properties including thermal behavior, thermal stability and mechanical properties were studied. The EM noise absorption ability was also investigated using micro-strip line method. At 1 GHz, the power loss of composite film with 150 ${\mu}m$ thickness was about 25%.

• Composites Research
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• v.20 no.5
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• pp.43-48
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• 2007

The absorption and the interference shielding of electromagnetic wave have been very important issues for commercial and military purposes. The stealth technique is one of the most typical applications of electromagnetic wave absorption technology. This study has started for the development of composite fillers containing dielectric and magnetic lossy materials. To improve the electromagnetic characteristics of conductive nano fillers, carbon nanofibers (CNFs) with nickel-phosphorous (Ni-P) or nickel-iron (Ni-Fe) have been fabricated by the electroless plating process. Observations by the electron microscopy (SEM/TEM) and element analyzer (EDS/ELLS) showed the uniform Ni-P and Ni-Fe coated CNFs. The compositions of the plating layers were about Ni-6wt%P and Ni-70wt%Fe, respectively. The average thicknesses of the plating layers were about $50\;{\sim}\;100\;nm$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.9 s.112
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• pp.821-828
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• 2006

In this paper, we investigated SAR(Specific Absorption Rate) value variation by the position and size of the loop-type ground located in a test mobile handset. We carried out simulations on SAR value with loop-type grounds in rear case of a mobile handset, and obtained results showed that different positions and sizes of loop-type grounds had different SAR values. Among investigated positions and sizes of loop-type grounds, the small size case-C showed the best performance; i.e., it showed a decrease efficiency of 8.70 %. And in this case, it showed the highest induced electric-field distribution in the loop-type ground. In the simulation, the folding angle was set to $160^{\circ}$.

• Journal of the Korean Magnetics Society
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• v.27 no.2
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• pp.49-53
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• 2017

Metamaterials composed of split cut wire (SCW) on grounded polyimide film substrate have been investigated for the aim of electromagnetic wave absorbers operated in THz frequency band. Reflection loss and current density distributions are numerically simulated with variations of the SCW geometries using the commercial software. The minimum reflection loss lower than -20 dB has been identified at 5.5~6.5 THz. The simulated resonance frequency and reflection loss can be explained on the basis of the circuit theory of an inductance-capacitance (L-C) resonator. Dual-band absorption can be obtained by arrangement of two SCWs of different length on the top layer of the grounded substrate, which is due to multiple magnetic resonances by scaling of SCWs. With increasing the side spacing between SCWs, a more enhanced absorption peak is observed at the first resonance frequency that is shifted to a lower frequency.

• Journal of Navigation and Port Research
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• v.34 no.7
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• pp.539-542
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• 2010

In this paper, we designed and fabricated the Electro-Magnetic (EM) wave absorber for wireless LAN by using Amorphous and CPE. The material constants and the absorption properties were measured for the samples containing 50 %, 60 %, and 70 % weight fraction of Amorphous. Moreover, the EM wave absorption abilities were simulated for the EM absorbers in different thicknesses by adopting the measured permittivity and permeability, and then the EM wave absorber was fabricated based on the simulated design values. As a result, the EM wave absorber with the composition ratio in Amorphous : CPE = 60 : 40 wt.% with the thickness of 4 mm has the absorption ability more than 35 dB at 2.4 GHz. Thus, it is expected the wireless LAN environment can be improved by using the developed absorber.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.235.1-235.1
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• 2015

Artificially-engineered materials, whose electromagnetic properties are not available in nature, such as negative reflective index, are called metamaterials (MMs). Although many scientists have investigated MMs for negative-reflective-index properties at the beginning, their interests have been extended to many other fields comprising perfect lenses. Among various kinds of MMs, metamaterial absorbers (MM-As) mimic the blackbody through minimizing transmission and reflection. In order to maximize absorption, the real and the imaginary parts of the permittivity and permeability of MM-As should be adjusted to possess the same impedance as that of free space. We propose a dual-wide-band and polarization-independent MM-A. It is basically a triple-layer structure made of metal/dielectric multilayered truncated cones. The multilayered truncated cones are periodically arranged and play a role of meta-atoms. We realize not only a wide-band absorption, which utilizes the fundamental magnetic resonances, but also another wide-band absorption in the high-frequency range based on the third-harmonic resonances, in both simulation and experiment. In simulation, the absorption bands with absorption higher than 90% are 3.93 - 6.05 GHz and 11.64 - 14.55 GHz, while the experimental absorption bands are in 3.88 - 6.08 GHz and 9.95 - 13.84 GHz. The physical origins of these absorption bands are elucidated. Additionally, it is also polarization-independent because of its circularly symmetric structures. Our design is scalable to smaller size for the infrared and the visible ranges.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.91-101
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• 2004

SAR(Specific Absorption Rate: 전자파 흡수율)이란 생체조직이 단위 질량당 흡수하는 전력(W/kg)으로 ICNIRP(International Commission on Non-ionizing Radiation Protection: 국제비전리방사위원회)국제 규격에서는 10 g평균 첨두 SAR 값을 인체 전신 및 국부(두부 및 몸통)에 대해 각각 0.08 W/kg과 2 W/kg으로 규정하고 있고, 미국의 FCC 규격에서는 국부노출의 경우 1 g 평균 첨두 SAR 값을 1.6 W/kg 값으로 제한하고 있다. (중략)

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.425-428
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• 2005

A variety of wireless devices are commercially available now. Most of studies, however, have been directed to the biological effects of mobile-phone EMF. In this study, dosimetric analysis for wireless devices of head-mounted display type and a wristwatch type were made to investigate possible biological effects of these devices. SAR (Specific Absorption Rate) distributions were calculated using FDTD (Finite Difference Time Domain) method, for adult human models such as standard Korean human model and VHP(Visible Human Project) model, as well as scaled models. Measurements were also performed for SAM phantom wearing a simplified prototype for a wireless device for validation of the simulation results. It has been found that children are more vulnerable to such exposure, and these devices could cause some biological effects for relatively lower power compared to conventional mobile pones.