• Journal of Navigation and Port Research
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• v.28 no.10 s.96
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• pp.869-874
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• 2004

Digital TV broadcasting's resolution or tone quality is very excellent than analog broadcasting and has many advantages including various multimedia functions such as home shopping, home banking, internet search, telecommuting, VOD, etc. In this study, it is essential to analyze the regional electromagnetic environment before Digital TV broadcasting, and therefore we analyzed Busan area's limitation using ETRI propagation model. For maintaining high-quality Digital TV signals, we measure electric field intensity wide and far in Busan including mountains area and high-rise buildings. Generally, it has lower value by a standard ETRI propagation model than simulated value about standard model, but distribution pattern are similar with it. Compared theoretical values with the measured results, they have similar values for flat area but very different values for crowded city area and mountains area So we conclude that ETRI propagation model and theoretical model are not suitable for Busan in a free space.

• Journal of Astronomy and Space Sciences
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• v.25 no.1
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• pp.43-52
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• 2008

As the next generation of global satellite navigation system, the Galileo project is about to witness an initial orbit validation stage as the successful test of navigation message transmission from Giove-A in 2007. The Space Geodesy division ana the Radio Astronomy division of the Korea Astronomy & Space Science Institute had collaborated on the field survey for the Galileo Sensor Station (GSS) RF environment of the proposed site near Jeju Tamla University from August 3rd to August 5th, 2006. The power spectrums were measured in full-band $(800{\sim}2000MHz)$ and in-band (E5, E6 and L1 band) in frequency domain for 24 hours respectively. Finally, we performed a time domain analysis to characterize strong in-band interference source based on the result of the previous step.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.1
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• pp.47-53
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• 2004

For the purpose of comparison between the designed coverage and actual coverage of Korean DGPS (Differential Global Position System) beacon stations, we have received the ship‘s positions with states and IDs of their stations on the navigation route of Jeju-Tianjin by automatic selection mode of DGPS receiver and on them of Jeju-Inchun and Jeju-Vladibostok by manual mode. Also in case that some obstructions were on propagation routes from DGPS beacon stations to receiving positions, a restriction on available ranges of DGPS beacon signals was investigated. The results obtained are as follows : 1. The coverage of Korean DGPS beacon stations was designed 100NM (Nautical mails) at 40.0dB(over ${\mu}$V/m). But the actual coverages of them according to their stations and propagation routes were 0.3-3.6 times as wide as designed coverage. 2. In case that the propagation route of beacon signals from DGPS beacon stations was on the sea, the propagation distance of north direction from the stations was longer than south direction. 3. The coverages of Echongdo and Ulungdo stations were 366NM on the yellow sea and 342.3NM on the east sea of Korea respectively, and were widest than any other stations. 4. The coverage of Marado station on the south and yellow seas of Korea was very unstable because of the Halla mountain on the propagation route. Maximum receiving range to be measured by automatic selection mode of DGPS receiver was 145NM on the route of Jeju-Tianjin on June 22-July 1, 2002. Minimum receiving range to be not measured by manual selection mode was 28.7NM on the route of Jeju-Inchun on June 26-28, 2003

• Journal of Advanced Navigation Technology
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• v.19 no.1
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• pp.60-65
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• 2015

In the present study, compact $0^{th}$ order resonant antenna for 2.4 GHz ISM frequency band is newly proposed. In case of wireless communication systems such as wi-fi, bluetooth and Zigbee, antennas with omni-directional radiation pattern are necessary because of the demands for uniformly received electric field strength without variation for direction. It is well-known that $0^{th}$ order resonant antennas are not only advantageous for miniaturization but also have advantage of maintaining omni-directional radiation pattern. The proposed antenna is composed of two-element array in which the size of unit element should be smaller than ${\lambda}/4$ correspondent to the resonant length of typical monopole antennas The proposed antenna which is placed at middle and upper side of PCB with $50{\times}50mm^2$ size is designed and fabricated within limited space of $8{\times}5mm^2$. The measured impedance bandwidth ($S_{11}{\leq}-10dB$) is about 100 MHz (2.4~2.5 GHz) which corresponds to quite wide bandwidth in comparison with the antenna size, and also the measured peak gain over the passband is more than 3 dBi which is thought to be slightly wider than the other $0^{th}$ order resonant antenna.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.389.1-389.1
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• 2014

최근의 환경 및 에너지에 대한 관심으로 수요가 증가하고 있는 하이브리드 및 전기 자동차나 태양광발전, 풍력발전용의 인버터기기에는 고에너지밀도 커패시터가 필수적이 되었다. 높은 에너지 밀도를 요구하는 전력전자, 펄스파워 등의 응용분야에 사용되는 고에너지밀도 커패시터는 PET (Polyethylene terephtalate)와 PP (Polypropylene)와 같은 폴리머 유전체를 사용하는 범용 필름 커패시터가 사용되었으나 사용 요구 조건의 한계에 도달하여, 새로운 유전체를 적용하는 커패시터가 절실히 필요한 상황이다. PET와 PP와 같은 유전체는 유전상수가 2~3의 낮은 값을 가지고 있어 고에너지밀도를 구현하기가 어렵다. 본 연구에서는 새롭게 요구되고 있는 고에너지 밀도 커패시터의의 성능을 만족시키기 위하여 $20{\sim}50{\mu}m$ 두께의 PET 필름상에 세라믹 유전체인 $ZrO_2$ 박막을 스퍼터(Sputter) 증착법에 의해 코팅하여 종래의 필름 커패시터와 세라믹 커패시터의 장점을 갖는 커패시터를 제조하기 위한 박막 유전재료의 개발을 목표로 하였다. 수백 nm~수 ${\mu}m$ 두께의 $ZrO_2$ 박막을 스퍼터링 공정조건에 따라 증착한 후 박막의 결정성, 기판과의 부착성, 증착속도, 유전상수, 절연파괴강도, 온도안정성 등을 XRD, SEM, AFM, EDS, XPS, Impedance analyzer 등에 의해 평가하였다. $ZrO_2$ 유전체막은 상온에서 증착하였음에도 정방정(tetragonal)구조의 결정질로 성장하였고 증착압력이 증가함에 따라 주피크의 세기가 감소하였다. 증착 중 산소가스를 주입하였을 경우에도 결정질막으로 성장하였다. 증착막들은 산소가스의 양이 증가함에 따라 짙은 흰색으로 변하였으며 PET 기판과의 접착력도 약해졌다. 또한 거칠기는 Ar가스만으로 증착한 경우보다 증가하였으며 24~66 nm의 평균 거칠기값을 보였다. PET위에 Ar가스만으로 증착한 $ZrO_2$의 비유전율은 1kHz에서 116~87의 비유전율을 보여 PET에 비해 매우 우수한 특성을 보였다. $ZrO_2$ 막들은 300kV/cm의 전계에서 대략 10-8A 이하의 누설전류를 보였다. 증착가스비를 달리하여 제조된 시편에서도 유사한 누설전류값을 나타내었다. 300 kV/cm 전후의 전계까지 측정한 $ZrO_2$ 막의 P-E (polarization-electric field) 특성을 확인하였는데, 5 mTorr의 압력에서 증착한 막은 253 kV/cm에서 $5.5{\mu}C/cm^2$의 분극값을 보였다. P-E커브의 기울기와 분극량에 따라 에너지밀도가 달라지므로 공정조건에 따라 에너지밀도가 변화됨을 예측할 수 있었다. PET위에 스퍼터 증착한 $ZrO_2$ 유전체막은 5mTorr의 Ar가스분위기에서 제조할 때 가장 안정적인 구조를 보였으며, 고에너지밀도 커패시터에의 적용가능성을 보였다.

• Journal of Food Hygiene and Safety
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• v.15 no.1
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• pp.13-17
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• 2000

The low salt seasoned jeotkal, salted and fermented fisheries product, may has some problems, such as short shelf-life, its putrefaction by mixing some microorganism from additives. It was considered that most microorganism in seasoned jeotkal were introduced from red pepper powder. Therefore, it is important to pasteurize red pepper powder for improving its microbial quality. When red pepper powder was pasteurized by ohmic heating, the survival cell concentration in red pepper powder was reduced to 1-log-unit at 500 V/m, 700 V/m, above 8$0^{\circ}C$. But viable cell counts were reduced from 8.5$\times$10$^{6}$ CFU/g to 2.1 $\times$ 10$^2$CFU/g, i.e. 4.6-log-unit, during ohmic heating at 9$0^{\circ}C$ for 40 min. Color values of red pepper powder during ohmic heating with different holding time were not changed significantly. When squid-jeotkal was manufactured by using the pasteurized red pepper powder, viable cell counts of the product were decreased by about three log cycles, compare with control product. And also the counts of fungi were significantly decreased.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.65-74
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• 1993

A miniature size electrostatic induction motor has been fabricated and studied with emphasis on the role of the surface resistivity, the relative dielectric constant and the charge relaxation time constant of the rotor surface materials and the rotor liner materials, which, however, control the surface charge induction and relaxation on the rotor material surface and the field intensity between the rotor and the stator of the motor. It is found that the surface resistivity and/or the relative dielectric constant, and the charge relaxation time constant of the rotor surface material enfluenced significantly to motor speed controlled by the surface charge induction and relaxation on the rotor surface depending on the applied voltage and/or frequency changing. The resistivity of the rotor liner material is also found to be effected to the motor speed greatly by control of the field intensity between the rotor and the stator and of the surface charge distribution of the induced charge on the rotor. As a result, a maximum no load rotor speed of the motor tested was about 5500 rpm at the applied voltage of 4.5 kV and the frequency of 220 Hz for the case of the rotor surface material of $BaTiO_{3}$ 80% in the resin binder layered on the copper-foil rotor liner material.

• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.207-214
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• 2005

This paper presents a channel structure for promising high performance pseudomorphic high electron mobility transistor(pHEMT) switching device for design and fabricating of microwave control circuits, such as switches, phase shifters, attenuators, limiters, for application in personal mobile communication systems. Using the designed epitaxial channel layer structure and ETRI's $0.5\mu$m pHEMT switch process, single pole double throw (SPDT) Tx/Rx monolithic microwave integrated circuit (MMIC) switch was fabricated for 2.4 GHz and 5 GHz band wireless local area network (WLAN) systems. The SPDT switch exhibits a low insertion loss of 0.849 dB, high isolation of 32.638 dB, return loss of 11.006 dB, power transfer capability of 25dBm, and 3rd order intercept point of 42dBm at frequency of 5.8GHz and control voltage of 0/-3V These performances are enough for an application to 5 GHz band WLAN systems.

• Composites Research
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• v.37 no.3
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• pp.209-214
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• 2024

Graphene oxide (GO), known for its high stiffness, thermal conductivity, and electrical conductivity, is being utilized as a reinforcement in nanocomposite materials. This study evaluates the mechanical properties of epoxy nanocomposites incorporating GO and edge modified GO (E-GO), which has hydroxyl groups substituted only on its edges. GO/E-GO was uniformly dispersed in epoxy resin using ultrasonic dispersion, and mechanical properties were assessed through tensile testing. The results showed that the addition of nanoparticles increased both tensile strength and toughness. The tensile strength of the epoxy without nanoparticles was 74.4 MPa, while the highest tensile strength of 90.7 MPa was observed with 0.3 wt% E-GO. Additionally, the modulus increased from 2.55 GPa to 3.53 GPa with the addition of nanoparticles. Field emission scanning electron microscopy of the fracture surface revealed that the growth of cracks was impeded by the nanoparticles, preventing complete fracture and causing the cracks to split in multiple directions. E-GO, with surface treatment only on the edges, exhibited higher mechanical properties than GO due to its superior dispersion and surface treatment effects. These results highlight the importance of nanoparticle surface treatment in developing high-performance nanocomposite materials.

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.653-659
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• 2005

When emulsion is irradiated by a microwave, the energy absorbed by the emulsion is proportional to irradiation time. In case of a long exposure, the temperature of emulsion rises, its viscosity decrease, and subsequently increase the rate of demulsification. In this work, in order to improve demulsification rate, the studies on demusification and the Sauter mean diameter ($D_{32}$) for each microwaved emulsion with different irradiation mode(continuous, pulsative, and periodical irradiation) have been carried out. When the 30% W/O emulsion (sample #1) was irradiated for 600 sec and settled for 24 h, oil recovery rates from continuous, pulsative, and periodical microwave irradiation were 60.0%, 62.3%, and 96.2%, and the amounts of separated water were 26.5%, 35.0%, and 93.9%, respectively. Also, the Sauter mean diameters ($D_{32}$) were $47.183{\mu}m$, $111.547{\mu}m$, and $220.476{\mu}m$, respectively.