• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.619-626
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• 2000

The electromagnetic fields of the corrugated annular feed-horn antenna have been analyzed exactly by using the finite-difference time-domain (FDTD) technique. The radiation pattern and return loss characteristics of the antenna were obtained as a function of the impedance of feeding coaxial line at 11.8GHz. The return loss was determined to be less than -25dB at 30$\Omega$. It was confirmed that the phase error is less compared to that of the antenna without corrugation, but the directivity of the radiation pattern needs to be improved.

• ETRI Journal
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• v.41 no.6
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• pp.731-738
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• 2019

We proposed a novel electromagnetic band-gap (EBG) cell-embedded antenna structure for reducing the interference that radiates at the antenna edge in wireless access in vehicular environment (WAVE) communication systems for vehicle-to-everything communications. To suppress the radiation of surface waves from the ground plane and vehicle, EBG cells were inserted between micropatch arrays. A simulation was also performed to determine the optimum EBG cell structure located above the ground plane in a conformal linear microstrip patch array antenna. The characteristics such as return loss, peak gain, and radiation patterns obtained using the fabricated EBG cell-embedded antenna were superior to those obtained without the EBG cells. A return loss of 35.14 dB, peak gain of 10.15 dBi at 80°, and improvement of 2.037 dB max at the field of view in the radiation beam patterns were obtained using the proposed WAVE antenna.

• 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.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.478-483
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• 2023

This study examined the corrosion behavior of bimetal materials composed of Fe-Ni alloy and Fe-Ni-Mo alloy, both suitable for use in electromagnetic switches. Electrochemical polarization and weight loss measurements revealed that, in contrast to Fe-Ni alloy, which exhibited pseudo-passivity behavior, Fe-Ni-Mo alloy had higher anodic current density, displaying only active dissolution and greater weight loss. This indicated a lower corrosion resistance in the Fe-Ni-Mo alloy. Equilibrium calculations for the phase fraction of precipitates suggested that the addition of 1 wt% Mo may lead to the formation of second-phase precipitates, such as Laves and M₆C, in the γ matrix. These precipitates might degrade the homogeneity of the passive film formed on the surface, leading to localized attacks during the corrosion process. Therefore, considering the differences in corrosion kinetics between these bimetal materials, the early degradation caused by galvanic corrosion should be prevented by designing a new alloy, optimizing heat treatment, or implementing periodic in-service maintenance.

• Composites Research
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• v.28 no.6
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• pp.333-339
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• 2015

Electromagnetic interference shielding composite with low density ($1.18g/cm^3$) was fabricated using electroless plated FeCo magnetic metal hollow fibers and ethylene propylene diene monomer (EPDM) polymer. Aspect ratio of the fibers were controlled and their hollow structure was obtained by heat treatment process. The FeCo hollow fibers were then mixed with EPDM to manufacture the composite. The higher aspect ratio of the magnetic metal hollow fibers resulted in high electromagnetic interference shielding effectiveness (30 dB) of the composite due to its low sheet resistance (30 ohm/sq). The enhanced electromagnetic interference shielding effectiveness was mainly attributed to the formation of conducting network over the percolation threshold by high aspect ratio of fibers as well as an increase of the reflection loss by impedance mismatch owing to low sheet resistance, absorption loss, and multiple internal reflections loss.

• ETRI Journal
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• v.40 no.4
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• pp.546-553
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• 2018

Since the Gyeongju earthquakes in 2016, there have been increased research interests in the areas of seismic design, building collapse, and rescue radar applications in Korea. Ground penetrating radar (GPR) is a nondestructive electromagnetic method that is used for underground surveys. To properly design ground penetrating radar that detects buried victims precisely, it is important to study electromagnetic wave propagation channel characteristics in advance. This work presents an electromagnetic propagation environment analysis of a trapped victim for GPR applications. In this study, we develop a realistic collapse model composed of layered reinforced concrete and a victim positioned horizontally. In addition, the effects of rebars and the distance between the radar antenna and target are investigated. The numerical analysis presents the electromagnetic wave propagation characteristics, including amplitude loss and phase difference, in the 450-MHz and 1,500-MHz frequency band, and it shows the electric field distribution in the environment.

• Korean Journal of Materials Research
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• v.29 no.6
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• pp.363-370
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• 2019

The recent development of information and communication technologies brings new changes to automobile traffic systems. The most typical example is the advancement of dedicated short range communication(DSRC). DSRC mainly consists of an intelligent transportation system(ITS), an electronic toll collection system(ETCS) and an advanced traveler information system(ATIS). These wireless communications often cause unnecessary electromagnetic waves, and these electromagnetic waves, in turn, cause frequent system malfunction. To solve this problem, an absorber of electromagnetic waves is suggested. In this research, various materials, such as powdered metal and iron oxides, are used to test the possibility for an effective absorption of the unnecessary electromagnetic waves. The various metal powders are made into a thin sheet form by compositing through processing. The electromagnetic characteristics(complex permittivity, complex permeability) of the fabricated sheet are measured. As a result, we achieve -6.5 dB at 940 MHz(77.6 % absorption rate) with a 1.0 mm-thickness electromagnet wave absorber, and -9.5 dB at 940 MHz(88.8 % absorption rate) with a 2.0 mm-thickness absorber.

• Journal of electromagnetic engineering and science
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• v.6 no.2
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• pp.110-116
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• 2006

A reflective array type surface acoustic wave(SAW) dispersive delay line(DDL) with high time-bandwidth at the V/UHF-band is designed and fabricated for compressive receiver applications. This type of the SAW DDL has the properties of the relative bandwidth of 20 %, the time delay of 49.89 usec, the insertion loss of 38.5 dB and the side lobe rejection of 39 dB. In comparison with a commercial SAW DDL, the insertion loss, amplitude ripple and side lobe rejection are improved by $1.5dB{\pm}0.6dB$ and 4 dB respectively. Using the fabricated SAW DDL, the prototype of the compressive receiver is developed. It is composed of RF converter, fast tunable LO, chirp LO, A/D converter, signal processing unit and control unit. This prototype system shows a fine frequency resolution of below 30 kHz with high scan rate.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.1-5
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• 2010

A spurious suppressed bandpass filter is proposed and discussed using the stepped impedance resonator(SIR) on a substrate-integrated waveguide(SIW) structure with a double-layer substrate. The second resonance of the fundamental $TE_{10}$ mode can be controlled by adjusting the electrical length and impedance ratio of each SIR. The spurious suppressed SIW bandpass filter shows the measurement results of the insertion loss of 3.98 dB and return loss of less than 11.58 dB at the center frequency of 12 GHz. Also, the second spurious frequency is improved to about $1.5f_0$ compared with $1.33f_0$.

• Journal of electromagnetic engineering and science
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• v.3 no.1
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• pp.12-16
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• 2003

In this paper, low noise amplifiers with coplanar waveguide structure are presented for Wireless LAN data communication application. For comparison of microwave performance, LNAs of cascode type and balanced type using cascode cell with the same substrate and same bias conditions are designed and implemented. A cascode type of LNA shows the gain of 12.45 ㏈, input return loss of 11.63 ㏈, and noise figure of 1.52㏈. A balanced type of LNA using cascode cell shows the gain of 6.58 ㏈, input return loss of 16.6 ㏈, and noise figure of 1.18 ㏈.