• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.582-591
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• 2000

In this paper, the Finite-Difference Time-Domain(FDTD) modeling method of the Korean human head is introduced to calculate electromagnetic energy absorption for the human head by mobile phones. After MRI scanning data is obtained, 2 dimensional(2D) segmentation is done from the 2D MRI image data by the semi-automatic method. Then, 3D dense segmentation data with $1mm\times1mm\times1mm$ is constructed from the 2D segmentation data. Using the 3D segmentation data, coarse FDTD models of human head that is tilted arbitrarily to model the condition of tilted usage of mobile phone.

• Carbon letters
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• v.27
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• pp.90-97
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• 2018

Electromagnetic interference (EMI) shielding is an important issue in modern daily life due to the increasing prevalence of electronic devices and their compact design. This study estimated EMI-shielding effect (EMI-SE) of small ($8-14{\times}17mm$) Hanji (Korean traditional paper) doped with carbon nanotubes (CNTs) and compared to Hanji without CNT using $^2H$ (92.1 MHz) and $^{23}Na$ (158.7 MHz) nuclear magnetic resonance (NMR) peak area data obtained from 1 M NaCl in $D_2O$ samples in capillary tubes that were wrapped in the Hanji samples. The simpler method of using the variation of reflected power and tuning frequency by inserting the sample into an NMR coil was also tested at 242.9, 158.7, and 92.1 MHz. Overall, EMI shielding was relatively more effective at the higher frequencies. Our results validated that NMR methods to be useful to evaluate EMI-SE, particularly for small, flexible shielding materials, and demonstrated that EMI shielding by absorption is dominant in Hanji mixed with CNT.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.3
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• pp.294-301
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• 2016

In this paper, we designed the transparent circuit analog radar absorbing structure using printed metal grid mesh for enhanced optical transmittance. To obtain wideband electromagnetic absorption and enhanced optical transparency at X-band, we proposed the resistive FSS(Frequency Selective Surface) using printed metal mesh pattern on transparent glass with PEC(Perfect Electric Conductor) plane using ITO(Indium Thin Oxide) coating. We then fabricated the proposed structure to verify the simulation results obtained from commercial EM simulator. The comparisons between the simulation and measured results show good agreements. The results also show that the proposed radar absorbing structure can provide wideband reflection as well as better optical transparency. We can apply this proposed structure to the canopy of stealth aircraft and other stealth and security applications for visible transparency.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.8 s.185
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• pp.100-107
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• 2006

The objective of this research is to investigate the electromagnetic interference(EMI) shielding characteristics of fiber reinforced composites. We fabricated glass and carbon fiber reinforced composites filled with metal powder and nano carbon black. The measurements of shielding effectiveness(SE) were carried out frequency range 300MHz - 1GHz for commercial purposes such as electric or telecommunication devices. The return loss and loss due to absorption were also measured as a function of frequency in the micro wave(300MHz-1GHz) region. It is observed that the SE of the composites is the frequency dependent, increase with the increases in filler loading. The Mg metal powder filled composite showed higher SE compared to that of carbon black. The Mg metal powder/epoxy composite was shown to exhibit up to 40dB of SE. The results indicates that the composite having higher filler loading can be used for the purpose of EMI shielding as well as for some microwave applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1224-1230
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• 2007

Recently, wireless LAN are often applied in home or office because of its various of convenience. Frequency rage of wireless LAN specified by IEEE 802.11a is at 5.2 GHz and IEEE 802.11b is 2.4 GHz. But in offices with wireless LAN devices, reflection of waves against walls, ceilings, floors and desks made of metal creates multipath problems that reduce communication speed and lose data. These problems can be solved by using EM wave absorber. In this paper, we designed and fabricated EM wave absorbers using MnZn-ferrite, sendust, carbon and CPE(Chlorinated Polyethylene). The EM wave absorber with the ratio of MnZn-Ferrite : sendust : CPE=64 : 16 : 20 wt.% has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz and the EM wave absorber with the ratio of MnZn-ferrite : carbon : CPE=40 : 15 : 45 wt.% has thickness of 3.8 mm and absorption ability more than 23 dB at 5.2 GHz.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.198-204
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• 2007

The effects of annealing temperature on electromagnetic wave absorption characteristics in $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ (at%) alloy flakes/polymer composite sheets available for quasi-microwave band have been investigated. The composite sheet including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ for 1 h exhibited highest power loss in the GHz frequency range as compared with the sheets composed of the alloy flakes annealed at higher temperature than $475^{\circ}C$ or in as-milled state. Moreover the imaginary part of complex permeability had largest value in the GHz frequency range for the sheets including the flakes annealed at $425{\sim}475^{\circ}C$. The large value of power loss of the sheets including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ was attributed to the high imaginary part of the complex permeability. However, because of its large transmission parameter $S_{21}$, the composite sheet having the magnetic flakes annealed at $525^{\circ}C$ showed low power loss.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.209-217
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• 2019

EMP (Electromagnetic Pulse) usually means High Power Electromagnetic Wave (HPEM). In the case of the shielding plate against the EMP, there is a possibility of deterioration of the electromagnetic wave shielding performance due to the skill of the constructor, bad construction, deformation of the shielding plate at the connection portion (joint portion). The inefficient use of space due to the separation distance is also pointed out as a problem. Therefore, this study aims to derive the optimum electromagnetic shielding condition by applying ATMSM to concrete as a part of securing electromagnetic wave shielding performance with reflection loss against concrete wall. Experimental parameters included concrete wall thickness and application of Zn-Al ATMSM. For the concrete wall, the wall thickness was 100 to 300mm, which is generally applied, and experimental parameters were set for the application of Zn-Al metal spraying method to evaluate electromagnetic shielding performance. Experimental results showed that as the thickness increases, the electromagnetic shielding performance increases due to the increase of absorption loss. In addition, after the application of Zn-Al ATMSM, the average shielding performance increased by 56.68 dB on average, which is considered to be increased by the reflection loss of the ATMSM. In addition, it is considered that the shielding performance will be better than that when the conductive mixed material and the ATMSM are simultaneously applied.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.3
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• pp.3-10
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• 1993

As a method to measure the absorbing characteristics of microwave absorber, various microwave measuring method can be used fundamentally. There is, however, a big problem in measuring errors, since the wavelength of microwave such as used for radar is very short. Therefor, this research aimed to design and fabricate a converting adaptor of 20mm .PHI. coaxial tube from a type-N connector to coaxial tube and to use it for evaluating absorption characteristics of microwave absorbor. Furthemore, the measurements of absorbing characteristics and material constants have been perfomed and reviewed, which were carried out by using the coaxial and by using rectangular waveguide, respectively. As a result, the validity of the proposed measuring method has been conformed. In this paper, a preliminary evalua- tion on the characteristics of the electromagnetic wave absorbor for X-band radar designed and fabricated for a laboratory use is performed by reflected power method near to a pratical use. Then for field test by using X-band radar is carried out with real target of $1.2m\times1.2m$ in size. As the result of the above, the usefullness of the designed and fabricated electromagnetic wave absorber in paint type for X-band radar has been confirmed.

• Journal of Powder Materials
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• v.22 no.4
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• pp.234-239
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• 2015

Electronic products are a major part of evolving industry and human life style; however most of them are known to emit electromagnetic waves that have severe health hazards. Therefore, different materials and fabrication techniques are understudy to control or limit transfer of such waves to human body. In this study, nanocomposite powder is dispersed into epoxy resin and shielding effects such as absorption, reflection, penetration and multiple reflections are investigated. In addition, nano size powder (Ni, $Fe_2O_3$, Fe-85Ni, C-Ni) is fabricated by pulsed wire evaporation method and dispersed manually into epoxy. Characterization techniques such as X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy are used to investigate the phase analysis, size and shape as well as dispersion trend of a nano powder on epoxy matrix. Shielding effect is measured by standard test method to investigate the electromagnetic shielding effectiveness of planar materials, ASTM D4935. At lower frequency, sample consisting nano-powder of Fe-85%Wt Ni shows better electromagnetic shielding effect compared to only epoxy, only Ni, $Fe_2O_3$ and C-Ni samples.

• Journal of the Korean Magnetics Society
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• v.10 no.2
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• pp.86-92
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• 2000

The spin wave absorption spectra are obtained by a simultaneous solution of the Maxwell equation and the Gilbert equation considering the boundary condition of electromagnetic wave and magnetization in the film surfaces. The physical parameters that influence the absorption energy are thickness, exchange stiffness constant, surface magnetic anisotropy, magnetization. damping factor, electric resistivity of the thin film. We investigated how these parameters affect the resonance field, the linewidth and the intensity of the spin wave spectrum.