• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.289-295
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• 2004

The relationship between friction characteristics and iron oxides at the sliding interface was investigated. Three friction materials containing iron, magnetite $(Fe_3O_4)$ or hematite $(Fe_2O_3)$ were manufactured and friction tests were performed on gray cast iron disks to evaluate the friction coefficient as a function of sliding speed $\mu-\nu$. In-situ noise spectrum analyzer was employed to compare noise propensity during friction tests. Results show that the specimens with magnetite are more sensitive to velocity than those with iron or hematite. The specimens containing magnetite and hematite generated noise with different peaks in the spectrum. The difference in the peak frequency seems attributed to the different surface aggressiveness of iron oxides and intermittent changes of real contact area at the sliding interface during sliding. Surface morphology and roughness of the counter disc after the tests are also consistent with the aggressiveness of iron oxides.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.244-247
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• 2002

We examined a possibility to use inorganic plastic scintillator, which has the effective atomic number close to that of human soft tissue, for the measurement of dose distributions in a shorter time period. The method was to irradiate a block of plastic scintillator as a phantom, and to measure the distribution of the scintillation light by a wave length analyzer through a thread of plastic optical fiber. By irradiating the diagnostic x-ray, we observed the emission spectrum of the scintillation light from the scintillator. It showed a peak at around 420nm with a full width of 140 nm. The emission spectrum was integrated to determine the total number of photons. The dependences of the amount of photons on the irradiated dose were measured. The results of the experiment show that the amount of emission light is in proportional to the irradiated dose. From this fact, we conclude that the present method can be used for the measurement of the depth dose distribution of the diagnostic x-rays.

• 조명전기설비학회논문지
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• 제16권4호
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• pp.73-79
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• 2002

본 논문는 공기중 교류전압원을 이용하여 3종류의 전극부(침대평판전극, 평판대평판전극 및 구대평판전극부)에서 방전시 방사되는 방사전자파를 측정하고, 그 스펙트럼의 특이한 패턴을 나타냈다. 방사전자파의 측정은 스펙트럼분석기와 바이코니칼 안테나를 사용하여 VHF(30~230[MHz])대역에서 측정하였다. 방전개시전압영역일 때, 침대평판전극부인 경우에는 주파수 45, 70, 80[MHz] 대역에서, 평판대평판전극과 구대평판전극부인 경우에는 주파수40[MHz]에서 높은 전계강도를 나타내었다. 그러나 절연파괴전압영역일 때, 방사전자파의 주파수 스펙트럼분포는 전극의 형태에 따라 측정주파수 영역에서 차이를 나타내었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 C
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• pp.1878-1880
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• 2002

In this paper, electromagnetic waves radiated from discharge at three-type electrodes (needle-plane, plane-plane and sphere-plane electrode) using DC power source in air measured and the peculiar patterns of their spectra are reported. The radiated electrodmagnetic waves were measured in bandwidth of VHF($30{\sim}230$[MHz]) using a biconcal antenna and a spectrum analyzer. Frequency spectrum distribution of radiated electromagnetic wave was revealed under 50[MHz] at positive DC, and high electric field was shown at 45[MHz] frequency band. But, it was revealed under 70[MHz] frequency band at negative DC under plane-plane electrodes and sphere-plane electrodes, and high electric field was shown at 55 [MHz] frequency band.

• 한국진공학회지
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• 제6권1호
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• pp.97-102
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• 1997

이온-고체 표면 사이의 상호작용에 관한 연구를 수행하기 위하여 중 에너지 이온산 란 분광장치를 개발하였고 그 특성 평가를 수행하였다. 제작된 MEIS의 에너지 분해능은 $4\times 10^{-3}$으로 측정되었다. MEIS의 표면분석의 응용으로 60keVH+을 $Ta_2O_5$(300$\AA$)/Si에 적용하 여 에너지 손실인자와 깊이분해능을 얻은 결과는 42eV/$\AA$와 9.7$\AA$이었다. 또한, Si(100)표면 에 97.5KeV$H^+$이온을 random방향으로 입사시켜 이차원 스펙트럼을 얻었다.

• 전기전자학회논문지
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• 제23권2호
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• pp.606-613
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• 2019

본 논문에서는 파장 스위핑 레이저의 평탄 스위핑을 자동 유지하기 위한 새로운 방식을 제안하였다. 이 방식이 적용된 레이저의 제작 및 실험을 통하여 5시간이 경과하여도 평탄 스위핑 특성이 잘 유지되고 있음을 관찰하였다. 그리고 56nm의 스위핑 범위, 1kHz의 스위핑 주파수, 그리고 8.8mW 의 광 출력 파워도 확인하였다. 제안된 방식은 기존에 스위핑 레이저를 장시간 구동시킬 때 불가피하던 수동 편광 조절의 번거로움을 해소시키고 이 과정에서 요구되던 고가 광 스펙트럼 분석기의 사용을 배제시킨다.

• Journal of Radiation Protection and Research
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• 제11권1호
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• pp.3-14
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• 1986

$3'{\times}3'$ 원통형 NaI(T1) 검출기와 다중파고분석기(多重波高分析器)를 사용하여 측정한 $0.05{\sim}2.0MeV$ 구간의 ${\gamma}$선 spectrum에서 실(實)spctrum을 구하기 위하여 조사선량율(照射線量率)산출에 편리한 response matrix 방법을 사용하였다. Response mateix 구성에는, 위의 에네지 구간을 0.1 MeV의 등간격으로 나눈 $20{\times}20$ matrix로 한것과 검출기의 분해능이 입사 ${\gamma}$선 에너지의 평방근(平方根)에 의존한다는 가정하에 $0.1(MeV)^{1/2}$구간으로 나누어 $14{\times}14$ matrix로 구성한, 두가지 방법을 사용하였으며 그 역(逆)matrix들은 P-E 82/32 콤퓨터로 계산하였다. 이 방법으로 얻은 조사선량율은 에너지와 flux가 알려진 ${\gamma}$선량(陽)에 대하여 흔히 사용되는 계산방법으로 구한값과 10% 이내에서 일치하고 있으며, 선량측정학적(線量測定學的) 견지에서는 $E^{1/2}$ 구간으로 형성된 matrix가 등에너지간격으로 구성된 것보다 현실적인 것으로 판단되었다.

• 한국항행학회논문지
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• 제14권3호
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• pp.367-374
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• 2010

본 연구는 900MHz대역을 사용하는 TA(Talk-Around)와 RFID 시스템간의 주파수 공유 가능성에 대하여 연구하였다. TA의 FHSS(Frequency Hopping Spread Spectrum)방식에서의 변조방식은 FSK(Frequency Shift Keying)디지털 변조방식을 사용하고 있고 RFID는 ASK(Amplitude Shift Keying) 디지털 변조방식을 적용하고 있다. 주파수 공유 가능성에 대한 현장시험 대상 RFID시스템은 FHSS방식이었다. 현장시험은 다섯 가지의 시나리오에 의하여 진행되었다. 현장 시험용 RFID시스템은 미국제품으로 4개의 태그와 2개의 주 장치로 구성되었다. 테스트를 위하여 TA 4대와 에질런트 스펙트럼 아날라이져가 사용되었다. 변조방식의 차별화에 의한 주파수 공유 가능성을 이론적으로 분석하였다. 시뮬레이션 결과, 이론적으로 두 변조방식 간에 주파수 공유가 가능한 것으로 분석되었다. 현장시험결과에 의하여도 TA의 신호가 RFID 신호에 영향을 주지 않는 것으로 나타났다.

• 전기학회논문지P
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• 제51권3호
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• pp.120-125
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the switching-mode power converter, the output voltage is generally controlled by varying the duty ratio of main switch. When a converter operates in steady state, duty ratio of the converter is kept constant. So the power of switching noise is concentrated in specific frequencies. Generally, to reduce the EMI and improve the immunity of converter system, the switching frequency of converter needs to be properly modulated during a rectified line period instead of being kept constant. Random Pulse Width Modulation (RPWM) is performed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%~30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.422-424
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• 2002

The accuracy of DXA(Dual Energy X-ray Absorptiometry) highly depends on the detection and separation capability of dual energy X-ray X-ray photons. In addition both of scan time and patient exposure are affected by detection efficiency. A CZT detector with a good energy resolution and high detection efficiency was evaluated for the application of bone densitometry. Its performance was compared to a photomultiplier tube with a NaI(T1) scintillator in terms of energy resolution, detection efficiency and the accuracy of bone mineral density measurement. The comparison study was performed with CZT detector and PM tube using DXA equipments(OSTEO Plus, OSTEO Prima, ISOL Technology). The energy spectrum was acquired using MCA(Multi-Channel Analyzer). The used X-ray energy ranged from 20keV to 86keV. The MCA result of the CZT detector showed a slightly sharper energy spectrum than that of NaI(T1). Detection efficiency of the CZT detector at 59.5keV was 1.4 times better. Remarkably the final results of bone mineral density measurements demonstrate only less than 1% difference. The CZT detector appears to have many benefits for the application of bone densitometry. Its excellent energy resolution can enhance the counting accuracy of dual energy X-ray spectrum. Furthermore its compactness in physical dimension and no cooling requirement will be additional benefits for a more compact and accurate bone densitometer.