• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.262-270
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• 2004

Basic experiments were carried out using the THT-IV low-power Hall thruster to examine the influences of magnetic field shape and strength, and acceleration channel length on thruster performance and to establish guidelines for design of high-performance Hall thrusters. Thrusts were measured with varying magnetic field and channel structure. Exhaust plasma diagnostic measurement was also made to evaluate plume divergent angles and voltage utilization efficiencies. Ion current spatial profiles were measured with a Faraday cup, and ion energy distribution functions were estimated from data with a retarding potential analyzer. The thruster was stably operated with a highest performance under an optimum acceleration channel length of 20 mm and an optimum magnetic field with a maximum strength of about 150 Gauss near the channel exit and with some shape considering ion acceleration directions. Accordingly, an optimum magnetic field and channel structure is considered to exist under an operational condition, related to inner physical phenomena of plasma production, ion acceleration and exhaust plasma feature. A new Hall thruster was designed with basic research data of the THT-IV thruster. With the thruster with many considerations, long stable operations were achieved. In all experiments at 200-400 V with 1.5-3 mg/s, the thrust and the specific impulse ranged from 15 to 70 mN and from 1100 to 2300 see, respectively, in a low electric power range of 300~1300 W. The thrust efficiency reached 55 %. Hence, a large map of the thruster performance was successfully made. The thermal characteristics were also examined with data of both measured and calculated temperatures in the thruster body. Thermally safe conditions were achieved with all input powers.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.1-9
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• 2008

이 논문에서는 100[W]급 Discrete LED 투광기 조명 제품 개발에 관한 것으로, 3[W] RGBA LED를 이용하여 광색 및 색온도 제어가 가능하도록 광학/방열/회로/시스템 설계를 통한 시제품을 제작하였다. 그 결과, 색온도 $2,000{\sim}10,000[K]$ 범위에서 흑체궤적에 정확히 일치하면서 연색지수가 $71{\sim}91$까지 고연색성을 실현하였으며, 동작전압 $90{\sim}250[Vac]$, 효율 87[%], 역률 93이상의 양호한 전기적 특성을 나타냈다. 또한 투광기의 협각/중각/광자 배광을 만족하기 위하여 LED 렌즈를 설계하였으며, 신뢰성 확보 및 주위온도에 따른 광출력 변화를 최소화할 수 있는 방열설계를 실시하였다.

• 한국안전학회지
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• 제36권5호
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• pp.10-17
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• 2021

The controversy over the risk of the human body being affected by electromagnetic fields emitted from 60 Hz power lines continues without end. There are currently no new studies or research progress being made in this direction that is notable, and the number of civil complaints is gradually increasing. The problem is that each study produces different results, among which the effect of exposure to magnetic fields on childhood leukemia is a major one. In Korea, an electrician who was maintaining a 22.9 kV power line died of leukemia, which has recently been recognized as an occupational disease. Methods to reduce magnetic fields from power lines include shielding with wire loops, incorporating split phases and compaction techniques, installing underground power lines, converting to high-voltage direct current (HVDC), and increasing the ground clearance of transmission towers. Depending on whether a separate power supply is needed or not, there are two types of wire loops: passive loop and active loop. Magnetic field reduction is currently done through underground power lines; however, the disadvantage of this process is high construction costs. Installing passive loops, with relatively low construction costs, leads to lower magnetic field reduction rates than installing underground cables and a weakness to not solving the landscape problem. This methodological study aims at designing methods and reducing the effects of 2-wire set loops-the simplest and most practical. Since the method proposed in this study has been designed after analyzing the distribution of complex electromagnetic fields near the expected loop installation location, a practical design can be implemented without the need for any difficult optimization programming.

• 대한방사선기술학회지:방사선기술과학
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• 제42권1호
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• pp.19-24
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• 2019

For general radiological examinations, even in the same area and the same test, the test conditions must be set differently according to the patient. However, since it is impossible to consider the body shape and conditions of patients every time in medical institutions where various patients visit, the tests are conducted by setting the AEC which automatically sets the test conditions. AEC is most commonly used in chest radiography. Therefore, the purpose of this study is to propose the improvement plans for using AEC by measuring the exposure dose and evaluating the image quality according to whether the AEC is used or not, and to provide basic data for AEC research. In the present study, images were acquired while varying tube voltage and test distance according to the use of AEC in chest radiography. The radiation dose was measured by placing the dosimeter in front of the chest phantom, and the CNR and SNR of acquired images were analyzed using Image J. The t-test was conducted for the statistical analysis and the significance was determined at the level of 95%(p<.05). As a result of this study, in the inspection distance (100cm, 140cm, 180cm) according to the use of AEC, high doses were observed when the AEC was used and there was statistically significant difference(p<.05). In the t-test to determine the difference between CNR and SNR depending on whether AEC was used or not, there was no significant difference according to the use of AEC(p>.05). Therefore, when performing chest radiography, if the radiologist establishes the appropriate examination conditions and conducts the examination by not just relying solely on AEC, it may be possible to reduce unnecessary radiation exposure to the patient.

• 대한방사선기술학회지:방사선기술과학
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• 제44권3호
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• pp.261-267
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• 2021

As the number of Coronavirus Disease-19 (COVID-19) patients increases in a global pandemic situation, the usefulness of mobile computed tomography (CT) is gaining attention. Currently, mobile CT follows the basic safety and essential performance evaluation criteria of whole-body or limited-view X-ray CT in order to obtain device approval and evaluation in the Republic of Korea. Unlike stationary CT, mobile CT is not operated in shielded areas but rather areas such as intensive care units, operating rooms, or isolation rooms. Therefore, it requires a different basic safety and essential performance evaluation standard than stationary CT. In this study, four derived basic safety evaluation criteria related to electrical, mechanical, and radiation safety were included (dose indication test, protection against stray radiation, safety measures against excessive X-rays, half-value layer measurement); and seven essential performance evaluation criteria were included (tube voltage accuracy, mAs accuracy, radiation dose reproducibility, CT number of water, noise, uniformity, and spatial resolution); total eleven basic safety and essential performance evaluation criteria were selected. This study aims to establish appropriate basic safety and essential performance evaluation criteria for simultaneously obtaining images with diagnostic value and reducing the exposure of nearby patients, medical staff, and radiologic technologists during the use of mobile CT.

• 한국입자에어로졸학회지
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• 제18권1호
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• pp.1-8
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• 2022

Since 2019, the corona virus has been continuously affect human life. In particular, in the indoor space where people live, infection by airborne transmission of viruses is a problem. Among them, the spread in the subway, which is the main mode of transport for humans, can be serious. To solve this problem, our research team developed an ionic wind collector to collect and remove corona virus using an ionic wind collector and ozone. In order to apply the ionic wind collector to the subway, it must operate in two modes. Because large amounts of ozone are harmful to the human body. There is a mode that collects bio-aerosol from the air using ionic wind and a mode that inactivates viruses floating in the air by generating a large amount of ozone. As the applied voltage increased, the cleaning ability of the ionic wind collector increased, and the farther the distance between the discharge electrode and the ground plate, the higher the cleaning ability even at low current. In addition, clean air delivery rate (CADR) of an ionic wind collector was up to 5.5 m³/min. As a result of measuring the amount of ozone generated, it was confirmed that 50 ppb to 250 ppb was generated, and it was confirmed that ozone generation was controllable in the ionic wind dust collector.

• 한국결정성장학회지
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• 제31권6호
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• pp.258-263
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• 2021

ZnO 바리스터는 다결정구조를 가지는 반도체 소자로 결정립과 입계의 미세구조 제어를 통해 비선형적인 전류/전압 특성을 가지기 때문에 서지(surge)전압으로부터 회로를 보호하는 역할을 한다. 이러한 ZnO 바리스터에서 원하는 전기적 물성을 얻기 위해서는 소결 공정에서 미세구조의 제어가 중요하다. 따라서 소결 공정에서 중요한 변수들과 소결체의 전기적 물성인 유전율로 구성된 데이터셋을 정의한 후 실험계획법 기반으로 데이터를 수집했다. 수집된 실험데이터셋을 기계학습 알고리즘에 학습하여 메타모델을 개발했고, 개발된 메타모델에 수치기반 최적화 알고리즘인 HMA(Hybrid Metaheuristic Algorithm)를 적용하여 최대 유전율을 가질 수 있는 공정조건을 도출했다. 이러한 메타모델 기반의 최적화를 다변수 시스템인 세라믹공정에 적용한다면 최소한의 실험만으로 최적 공정조건 탐색이 가능할 것으로 판단된다.

• 한국의학물리학회지:의학물리
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• 제32권4호
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• pp.153-158
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• 2021

Purpose: This study evaluated the features of a pressure mapping system for patient motion monitoring in radiation therapy. Methods: The pressure mapping system includes an MS 9802 force sensing resistor (FSR) sensor with 2,304 force sensing nodes using 48 columns and 48 rows, controller, and control PC (personal computer). Radiation beam attenuation caused by pressure mapping sensor and signal perturbation by 6 and 10 mega voltage (MV) photon beam was evaluated. The maximum relative pressure value (mRPV), average relative pressure value (aRPV), the center of pressure (COP), and area of pressure distribution were obtained with/without radiation using the upper body of an anthropomorphic phantom for 30 minutes with 15 MV. Results: It was confirmed that the differences in attenuation induced by the FSR sensor for 6 and 10 MV photon beams were small. The differences in mRPV, aRPV, area of pressure distribution with/without radiation are about 0.6%, 1.2%, and 0.5%, respectively. The COP values with/without radiation were also similar. Conclusions: The characteristics of a pressure mapping system during radiation treatment were evaluated on the basis of attenuation and signal perturbation using radiation. The pressure distribution measured using the FSR sensor with little attenuation and signal perturbation by the MV photon beam would be helpful for patient motion monitoring.

• Smart Structures and Systems
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• 제29권5호
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• pp.653-660
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• 2022

Gravel scattering that is generated during operation of high-speed railway vehicle is cause to damage of vehicle such as windows, axle protector and so on. Especially, those are frequently occurred in winter season when snow ice is generated easily. Above all, damage of vehicle windows has not only caused maintenance cost but also increased psychological anxiety of passengers. Various methods such as heating system using copper wire, heating jacket and heating air are applied to remove snow ice generated on the under-body of vehicle. However, the methods require much run-time and man power which can be low effectiveness of work. Therefore, this paper shows that large-area heating system was developed based on heating coat in order to fundamentally prevent snow ice damage on high-speed railway vehicle in the winter season. This system gives users high convenience because that can remotely control the heating system using IoT-based wireless communication. For evaluating the applicability to railroad sites, a field test on an actual high-speed railroad operation was conducted by applying these techniques to the brake cylinder of a high-speed railroad vehicle. From the results, it evaluated how input voltage and electric power per unit area of the heating specimen influences exothermic performance to draw the permit power condition for icing. In the future, if the system developed in the study is applied at the railroad site, it may be used as a technique for preventing all types of damages occurring due to snow ice in winter.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2021년도 추계학술대회
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• pp.35-40
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• 2021

대부분의 비즈니스에서는 고객의 움직임에 대한 의미 있는 정보를 얻어낼 수 있는 유동인구 계측 데이터가 매우 중요하게 작용한다. 슈퍼마켓의 경우, 손님들의 수에 따라 계산대 수를 늘리거나 줄일 수 있다. 스마트 빌딩 또한, 각 객실의 수용 인원에 따라 냉난방 시스템을 제어하는 스마트 컨트롤러 같이 다양하게 적용될 수 있다. 카메라 기반 유동인구 계측 시스템과 같이 첨단 기술을 활용하여 보다 정확한 결과를 얻을 수도 있지만, 가격이 비싸고, 현장 설치가 어려우며, 사생활 침해의 문제가 발생하기도 한다. 본 논문에서는 특정 통로 혹은 IR 적외선 센서가 설치된 출입구의 유동인구 계측 방법을 제시한다. 나아가, 사람과 다른 물체를 구분하여 인식하는 방법을 제시하는데, 해당 솔루션은 저렴하고, 설치가 간편하며, 무엇보다 실시간 계측이 가능하다. 우리의 유동인구 계측 솔루션은 약 95%의 정확도를 보이고 있다.