• Proceedings of the Korean Reliability Society Conference
• /
• 2004.07a
• /
• pp.147-151
• /
• 2004

In this study, an optical fiber assembly directly coupled with a laser diode or a photo diode is designed to confirm high reliable optical coupling efficiency of optical transmitter(Tx) and receiver(Rx). The optical fiber assembly is fabricated by soldering an optical fiber and a Kovar ferrule using a glass solder after inserting an optical fiber through a Kovar ferrule. The Kovar which has good welding characteristics is applied to introduce laser welding technique. The glass solder has excellent thermal characteristics such as thermal shift delamination compared with PbSn, AuSn solder previously used usually. Furthermore, the glass solder doesn't need fiber metalization and this enables low cost fabrication. However, the glass soldering is high temperature process over 35$0^{\circ}C$ and the convex shape after solidification due to surface tension causes the stress concentration on optical fiber. The stress concentration on the optical fiber increases the optical insertion loss and possibility of crack formation. The shape of glass solder was designed referring to 2-D Axi-symmetric FEM simulation. To test the mechanical reliability, mechanical vibration test and shock test were done according to Telcorida GR-468-Core protocol. After each test, the optical loss of the stress distributed fiber assembly didn't exceed 0.5 dB, which passes the test.

• Journal of Korea Foundry Society
• /
• v.22 no.4
• /
• pp.160-166
• /
• 2002

The structure and properties of Fe-29Ni-17Co alloy which had been melted using induction furnace in air atmosphere and than electroslag-remelted were investigated. The oxygen content was reduced to 0.03% when the ingot was refined from $0.09{\sim}0.12%$ of that air melted. The amounts of spheroidal oxides inclusions and gas porosities of ingot were markedly reduced by the ESR process. CTE of ESR ingot contained small amount of oxides and porosities was found to be lower than that of AIM ingot, and tensile properties of ESR ingot and plate were found to be superior than that of AIM ingot and plate.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.65-69
• /
• 2002

An Al film deposited on the Kovar alloy substrate was anodically-bonded to the borosilicate glass, and the bond interfaces was closely investigated by transmission electron microscopy. Al oxide was found to form a layer ~l0 nm thick at the bond interface, and fibrous structure of the same oxide was found to grow epitaxially in the glass from the oxide layer. The fibrous structure grew with the bonding time. The mechanism of the formation of this fibrous structure is proposed on the basis of the migration of Al ions under the electric field. Penetration of Al into glass beyond the interfacial Al oxide was not detected. The comparison of the amount of excess oxygen ions generated in the alkali depletion layer with that incorporated in the Al oxide suggests that the growth of the alkali-ion depletion layer is controlled by the consumption of excess oxygen to form the interfacial Al oxide.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.241-241
• /
• 2010

적외선 센서는 빛의 유무에 관계없이 물체 또는 인체에서 발산하는 적외선을 감지한다. 이러한 센서를 전자 및 디스플레이 시스템과 연동하면 열영상 시스템이 되는데, 이는 전방 감시, 플랜트 감시, 보안, 방범용으로 많이 사용되며, 특히 자동차 야간 운전자 보조용으로 사용되어 최첨단, 고부가가치를 지니고 있는 핵심부품이다. 비냉각형 적외선 센서인 마이크로볼로미터는 상온에서 작동하므로 극저온 Cooler가 불필요하며, 무게와 부피가 작아 각종 시스템에 부착가능하다. 특히 볼로미터형 적외선 센서는 용량이 적은 TE cooler로 상온으로 안정화를 시키며, 진공으로 유지되는 금속 또는 세라믹 패키지를 사용하게 된다. 본 연구에서는 마이크로 볼로미터용 진공패키지를 제작하여 패키지 조립 및 측정기술에 대해 조사하였다. 패키지는 금속재질인 kovar를 사용하여 제작되었고, 내부에 TE Cooler와 장수명 진공유지를 위한 getter, 그리고 온도센서 및 볼로미터 센서 칩을 장착하여 조립하였다. 패키지 Cap ass'y와 base envelop의 솔더링 공정은 약 $200^{\circ}C$에서 수행하였으며, evacuation system을 이용하여 5일 동안 패키지 bake-out 공정을 수행하였다. 이 후 getter를 활성화시키고, seal-off 공정으로 진공 기밀을 유지하였다. 진공 패키지의 기밀성은 $6{\times}10^{-9}\;std.cm^3/sec$로 기밀성을 유지하였다. 볼로미터 센서의 반응도는 $10^2\;V/W$ 이상을 나타내었으며, 탐지도는 $2{\times}10^8\;cm-Hz^{1/2}/W$를 나타내었다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.2
• /
• pp.391-394
• /
• 2006

The paper deals with the experimental GNSS receiver built at the Czech Technical University for experiments with the real GNSS signal. The receiver is based on software defined radio architecture. Receiver consists of the RF front end and a digital processor based on programmable logic. Receiver RF front end supports GPS L1, L2, L5, WAAS/EGNOS, GALILEO L1, E5A, E5B signals as well as GLONASS L1 and L2 signals. The digital processor is based on Field Programmable Gate Array (FPGA) which supports embedded processor. The receiver is used for various experiments with the GNSS signals like GPS L1/EGNOS receiver, GLONASS receiver and investigation of the EGNOS signal availability for a land mobile user. On the base of experimental GNSS receiver the GPS L1, L2, EGNOS receiver for railway application was designed. The experimental receiver is also used in GNSS monitoring station, which is independent monitoring facility providing also raw monitoring data of the GPS, EGNOS and Galileo systems via internet.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.355-356
• /
• 2009

The change of thermal expansion and mechanical behaviors by cold working has been investigated in Fe-29%Ni-17%Co low thermal expansion Kovar alloy. Fe-29%Ni-17%Co alloy was cold rolled gradually and prepared to plates having reduction ratio of 0%, 20%, 40%, 60%, and 80%. Annealing effect on the properties was also studied. Thermal expansion was measured from $25^{\circ}C$ to $600^{\circ}C$ with a heating rate of $5^{\circ}C$/min by using vacuum differential dilatometer. It was found that thermal expansion coefficient ($\alpha_{30{\sim}400}$) slightly decreased (reduction ration of 20%) and then remarkably increased (above reduction ration of 40%) with increasing reduction ratio of cold rolling. Thermal expansion coefficient ($\alpha_{30{\sim}400}$) was sharply decreased after annealing heat-treatment. Yield and tensile strengths were continuously increased and elongation was decreased by cold roiling. Microstructural observation and X-ray diffraction analysis results showed that the $\alpha$ phase significantly increased as the reduction ratio increased. The slight decrease of thermal expansion coefficient bellow reduction ration of 20% could be explained by the destroying short-range ordering and the decreasing of grain size. The significant increase of thermal expansion coefficient with cold rolling mainly attributed to the appearance of $\alpha$ phase. The correlation between the microstructural cause and invar phenomena for the low thermal expansion behavior was also discussed.

• Nuclear Engineering and Technology
• /
• v.55 no.3
• /
• pp.1061-1070
• /
• 2023

Over the last few years, lead-free inorganic metal perovskites have gained impressive ground in empowering satellites in space exploration owing to their material stability and performance evolution under extreme space environments. The present work has examined the versatility of eight such perovskites as space radiation shielding materials by computing their photon, charged particles and neutron interaction parameters. Photon interaction parameters were calculated for a wide energy range using PAGEX software. The ranges of heavy charged particles (H, He, C, N, O, Ne, Mg, Si and Fe ions) in these perovskites were estimated using SRIM software in the energy range 1 keV-10 GeV, and that of electrons was computed using ESTAR NIST software in the energy range 0.01 MeV-1 GeV. Further, the macroscopic fast neutron removal cross-sections were also calculated to estimate the neutron shielding efficiencies. The examined shielding parameters of the perovskites varied depending on the radiation type and energy. Among the selected perovskites, Cs₂TiI₆ and Ba₂AgIO₆ displayed superior photon attenuation properties. A 3.5 cm thick Ba₂AgIO₆-based shield could reduce the incident radiation intensity to half its initial value, a thickness even lesser than that of Pb-glass. Besides, CsSnBr₃ and La_0.8Ca_0.2Ni_0.5Ti_0.5O₃ displayed the highest and lowest range values, respectively, for all heavy charged particles. Ba₂AgIO₆ showed electron stopping power (on par with Kovar) better than that of other examined materials. Interestingly, La_0.8Ca_0.2Ni_0.5Ti_0.5O₃ demonstrated neutron removal cross-section values greater than that of standard neutron shielding materials - aluminium and polyethylene. On the whole, the present study not only demonstrates the employment prospects of eco-friendly perovskites for shielding space radiations but also suggests future prospects for research in this direction.