• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.185-190
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• 1995

Rare earth-aluminum intermetallic compounds $RAI_{2}$ (R ; Lu, Ce, Gd) are prepared by the arc-melt method and the magnetic properties and electronic structures are investigated by magnetic susceptiptibiliy measurements using SQUID magnetometer. The magnetic suceptibiliyof $LuAl_{2}$ is weakly temperature dependent and shows a Pauli susceptibility of $10.1{\times}10^{-5}$ emu/mol, which means 3.2 states/eV/formula unit. On the other hand, the susceptibility data of $CeAl_{2}$ and $GdAl_{2}$ show a Curie-Weiss behavior for paramagnets. The magnetization data at low temperatures confirm that $CeAl_{2}$ undergoes an antiferromagnetic phase transition near 4 K whereas $GdAl_{2}$ a ferromagnetic transition at 170 K. The distinctive magnetic behaviors of $RAI_{2}$ originate from the different 4f band filling.

• Journal of Sensor Science and Technology
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• v.23 no.2
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• pp.110-113
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• 2014

In this paper, we propose and demonstrate a Fabry-Perot interferometer (FPI) optical fiber tip sensor fabricated by a blade-sawing technique using a fiber optic patch cord for high-resolution temperature measurement. The sensor head consists of a short air FP cavity near the tip of a single-mode fiber patch cord tip. The temperature which we can measure is determined through a phase variation of the interference fringes in the reflective spectrum of the sensor. The fiber optic FPI sensor in this work can monitor the environmental temperature very accurately from 40 to $120^{\circ}C$. As a result, the temperature sensitivity is obtained as $38.2pm/^{\circ}C$.

• Journal of Radiation Protection and Research
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• v.22 no.4
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• pp.263-272
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• 1997

A Radiation Alarm Monitor has been developed and manufactured in order to protect radiation workers from over-exposure. A visual and audible alarm system has been attached to initiate evacuation when accident occurs such as an unexpected change of radiation level or an over-exposure. The Radiation Alarm Monitor installed with microprocessor can record the information of radiation field change between 90 min. before the alarm and 30 min. after the alarm and also provide the data to an IBM compatible computer to analyze the accidents and to set a counterplan. It features a wide detection range of radiation field(10 mR/h-100 R/h), radiation field data storage, portability, high precision (${\pm}5%$) due to self-calibration function, and adaption of a powerful alarm system. According to ANSI N42.17A, the most stringent test standards, performance tests were carried out under various conditions of temperature, humidity, vibration, and electromagnetic wave hindrance at Korea Research Institute of Standards & Science (KRISS). As a result, the Radiation Alarm Monitor passed all tests.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.6
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• pp.153-162
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• 2009

This paper suggests the novel light-weight signal processing algorithm for wireless sensor network applications which needs low computing complexity and power consumption. Exponential average method (EA) is utilized by real time, to process the magnetometer signal which is analyzed to understand the own physical characteristic in time domain. EA provides the robustness about noise, magnetic drift by temperature and interference, furthermore, causes low memory consumption and computing complexity for embedded processor. Hence, optimal parameter of proposal algorithm is extracted by statistical analysis. Using general and precision magnetometer, detection probability over 90% is obtained which restricted by 5% false alarm rate in simulation and using own developed magnetometer H/W, detection probability over 60~70% is obtained under 1~5% false alarm rate in simulation and experiment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.313-319
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• 2017

Fiber optics sensors that have been mainly applied to aerospace areas are now finding applicability in other areas, such as transportation, including railways. Among the sensors, the fiber Bragg grating (FBG) sensors have led to a steep increase due to their properties of absolute measurement and multiplexing capability. Generally, the FBG sensors adhere to structures and sensing modules using adhesives such as an epoxy. However, the measurement errors that occurred when the FBG sensors were used in a long-term application, where they were exposed to environmental thermal load, required calibration. For this reason, the thermal curing of adhesives needs to be investigated to enhance the reliability of the FBG sensor system. This can be done at room temperature through cyclic thermal load tests using four types of specimens. From the test results, it is confirmed that residual compressive strain occurs to the FBG sensors due to an initial cyclic thermal load. In conclusion, signals of the FBG sensors need to be stabilized for applying them to a long-term SHM.

• Analytical Science and Technology
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• v.15 no.6
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• pp.496-501
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• 2002

The electrolyte cathode glow discharge (ELCAD) is a new optical system for direct determination of trace heavy metals in flowing water. ELCAD has been successfully developed for on-line monitoring of heavy metals in flowing water. The application of an atmospheric glow discharge between an electrolyte solution cathode and a platinum rod anode led to the development of stable discharge. The fundamental aspects of new plasma source have been investigated. The fundamental study of ELCAD system has been measured plasma temperature using Einstein-Boltzmann equation after searching Fe atomic emission lines. The spectrum of each elements such as Cu, Pb, Fe, Ni and Cr show only major elemental line and no ionic line possibly due to low temperature plasma source. The detection limits of each elements are also investigated. These informations show that this type of plasma may apply for monitoring of heavy metals in waste water which consists of complex matrix.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.261-261
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• 2016

플래시 메모리 (flash memory)는 DRAM(dynamic racdom access memory)이나 SRAM(static random access memory)에 비해 소자의 구조가 매우 단순하기 때문에 집적도가 높아서 기기의 소형화가 가능하다는 점과 제조비용이 낮다는 장점을 가지고 있다. 또한, 전원을 차단하면 정보가 사라지는 DRAM이나 SRAM과 달리 전원이 꺼지더라도 저장된 정보가 지워지지 않는다는 특징을 가지고 있어서 ROM(read only memory)과 정보의 입출력이 자유로운 RAM의 장점을 동시에 가지기 때문에 활용도가 크다. 또한, 속도가 빠르고 소비전력이 작아서 USB 드라이브, 디지털 TV, 디지털 캠코더, 디지털 카메라, 휴대전화, 개인용 휴대단말기, 게임기 및 MP3 플레이어 등에 널리 사용되고 있다. 특히, 낸드(NAND)형의 플래시 메모리는 고집적이 가능하며 하드디스크를 대체할 수 있어 고집적 음성이나 화상 등의 저장용으로 많이 쓰이며 일정량의 정보를 저장해두고 작업해야 하는 휴대형 기기에도 적합하며 가격도 노어(NOR)형에 비해 저렴하다는 장점을 가진다. 최근에는 smart watch, wearable device 등과 같은 차세대 디스플레이 소자에 대한 관심이 증가함에 따라 투명하고 유연한 메모리 소자에 대한 연구가 다양하게 진행되고 있으며 유리나 플라스틱과 같은 기판 위에서 투명한 플래시 메모리를 형성하는 기술에 대한 관심이 높아지고 있다. 전하트랩형 (charge trap type) 플래시 메모리는 플로팅 게이트형 플래시 메모리와는 다르게 정보를 절연막 층에 저장하므로 인접 셀간의 간섭이나 소자의 크기를 줄일 수 있기 때문에 투명하고 유연한 메모리 소자에 적용이 가능한 차세대 플래시 메모리로 기대되고 있다. 전하트랩형 플래시메모리는 정보를 저장하기 위하여 tunneling layer, trap layer, blocking layer의 3층으로 이루어진 게이트 절연막을 가진다. 전하트랩 플래시 메모리는 게이트 전압에 따라서 채널의 전자가 tunnel layer를 통해 trap layer에 주입되어 정보를 기억하게 되는데, trap layer에 주입된 전자가 다시 채널로 빠져나가는 charge loss 현상이 큰 문제점으로 지적된다. 따라서 tunnel layer의 막질향상을 위한 다양한 열처리 방법들이 제시되고 있으며, 기존의 CTA (conventional thermal annealing) 방식은 상대적으로 높은 온도와 긴 열처리 시간을 가지고, RTA (rapid thermal annealing) 방식은 매우 높은 열처리 온도를 필요로 하기 때문에 플라스틱, 유리와 같은 다양한 기판에 적용이 어렵다. 따라서 본 연구에서는 기존의 열처리 방식보다 에너지 전달 효율이 높고, 저온공정 및 열처리 시간을 단축시킬 수 있는 마이크로웨이브 열처리(microwave irradiation, MWI)를 도입하였다. Tunneling layer, trap layer, blocking layer를 가지는 MOS capacitor 구조의 전하트랩형 플래시 메모리를 제작하여 CTA, RTA, MWI 처리를 실시한 다음, 전기적 특성을 평가하였다. 그 결과, 마이크로웨이브 열처리를 실시한 메모리 소자는 CTA 처리한 소자와 거의 동등한 정도의 우수한 전기적인 특성을 나타내는 것을 확인하였다. 따라서, MWI를 이용하면 tunnel layer의 막질을 향상시킬 뿐만 아니라, thermal budget을 크게 줄일 수 있어 차세대 투명하고 유연한 메모리 소자 제작에 큰 기여를 할 것으로 예상한다.

• Journal of the Korean Magnetics Society
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• v.20 no.5
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• pp.187-190
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• 2010

$Sn_{0.99}{^{57}Fe}_{0.01}O_2$ prepared by a sol-gel method, and studied by x-ray diffractometer, vibrating magnetometer, Superconducting quantum interference devices and M$\ddot{o}$ssbauer spectroscopy. the crystal structure were found to be a rutile tetragonal structure with space group $P4_2$/mnm, and oxygen deficiency are 5.6 % by Rietveld refinement. magnetization value were $M_s=1.95{\times}10^{-2}{\mu}_B/Fe$ at room temperature, and Curri-weiss temperature were and ${\theta}_{cw}$ = 18 k, measurement of VSM and SQUID, respectively. Mssbauer spectra of $Sn_{0.99}{^{57}Fe}_{0.01}O_2$ have been Sextet taken at various temperatures ranging from 4.2 K to RT, and isomer shift value $\delta$ = 0.18~0.36 mm/s of $^{57}Fe$ ion site all of the temperature range the state shows ferric.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.701-706
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• 1999

The crystal structure and magnetic properties of magnetic oxide system (F $e_2$ $O_3$)$_{5}$(A $l_2$ $O_3$)$_{4-x}$(G $a_2$ $O_3$)$_{x}$)SiO has been studied using X-ray diffraction and Mossbauer spectroscopy The changes of magnetic structure by the Ga ion substitution and the temperature variation have been investigated using Mossbauer spectroscopy, and the results are compared with those of the SQUIB measurements. Results of X-ray diffraction indicated that the crystal structures of the system change from a cubic spinel type to an orthorhombic via the intermediate region. This magnetic oxide system seems to be new kind of spinel type ferrites containing high concentration of cation vacancies. Various and complicated Mossbauer spectra were observed in the samples (x>0.2) at temperatures lower than room temperature. This result could be explained by freezing of the superparamagnetic dusters. On cooling and substitution, magnetic states of the system show various and multicritical properties. Unexpected dip in magnetization curves below 50K was observed in SQUID measurements. It was interpreted as an effect of spin canting including spin freezing or collective spin behavior.ior.r.

• Korean Journal of Ecology and Environment
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• v.50 no.4
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• pp.411-421
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• 2017

Understanding the need for temperature regulation, behavior, and ecology of hibernating bats provides the possibility of conservation and management for target species. Our objective in this study was to improve understanding of the population trend and ecological requirement in Myotis formosus population in South Korea. From 2007 to 2016, total of 58 hibernacula for Myotis formosus were found across the country. Of the 58 hibernating sites of Myotis formosus, 86% (n=49) were abandoned mines and 14% (n=8) were natural caves. During the survey period, 28 (5%) bats of total 570 bats were observed in natural caves (n=8) and 542 (95%) bats were observed in abandoned mines (n=49). The internal environments of hibernacula of M. formosus were highly stable despite dramatic variation in the external environment. Specifically, we examined the population trend of the endangered bat Myotis formosus in South Korea by long-term monitoring for hibernation sites. The population trend of endangered species M. formosus showed a marked stable in hibernating population. Our results indicate that a tightly collected long-term data set may help to establish the initial approximation of population trends and manage to threats for the endangered bat species.