• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.4
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• pp.336-341
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• 2013

In this paper, the design concept of a low-temperature vacuum blackbody was described, and thermophysical model of the blackbody was numerically evaluated. Also the working performance of low-temperature vacuum blackbody was evaluated using infrared camera system. The blackbody system was constructed to operate under high-vacuum conditions ($2.67{\times}10^{-2}$ Pa) to reduce temperature uncertainty, which is caused by vapor condensation at low temperatures usually below 273 K. In addition, both heat sink and heat shield including cold shield were installed around radiator to prevent heat loss from the blackbody. Simplified mathematical model of blackbody radiator was analyzed using modified Stefan-Boltzmann's rule. The infrared radiant performance of the blackbody was evaluated using infrared camera. Based on the results of measurements, and simulation, temperature stability of the low-temperature vacuum blackbody demonstrated that the blackbody system can serve as a highly stable reference source for the calibration of an infrared optical system.

• Journal of radiological science and technology
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• v.40 no.3
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• pp.443-451
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• 2017

Mammography is commonly used for screening early breast cancer. However, mammographic images, which depend on the physical properties of breast components, are limited to provide information about whether a lesion is malignant or benign. Although a dual-energy subtraction technique decomposes a certain material from a mixture, it increases radiation dose and degrades the accuracy of material decomposition. In this study, we simulated a breast phantom using attenuation characteristics, and we proposed a technique to enable the accurate material decomposition by applying weighting factors for the dual-energy mammography based on a photon-counting detector using a Monte Carlo simulation tool. We also evaluated the contrast and noise of simulated breast images for validating the proposed technique. As a result, the contrast for a malignant tumor in the dual-energy weighted subtraction technique was 0.98 and 1.06 times similar than those in the general mammography and dual-energy subtraction techniques, respectively. However the contrast between malignant and benign tumors dramatically increased 13.54 times due to the low contrast of a benign tumor. Therefore, the proposed technique can increase the material decomposition accuracy for malignant tumor and improve the diagnostic accuracy of mammography.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.4
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• pp.195-200
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• 2020

With the growing interest in fossil fuel depletion and environmental pollution, railroad cars operating in Korea are in progress as the conversion from diesel to electric vehicles expands. The photovoltaic system, which is applied as an example of the conversion of electric vehicles, is infinite and pollution-free, and can produce energy without generating hazards such as air pollution, noise, heat, and vibration, and maintain fuel transportation and power generation facilities. There is an advantage that is rarely needed. However, the amount of electricity produced depends on the amount of solar radiation by region, and the energy density is low due to the power generation of about 25㎡/ kWp, so a large installation area is required and the installation place has limited problems. In view of these problems, many studies have been applied to fuel cells in the railway field. In particular, the plan to link the fuel cell power generation system railroad power supply system must be linked to the power supply system that supplies power to the railroad, unlike solar and wind power. Therefore, it has a close relationship with railroad cars and the linkage method can vary greatly depending on the system topology. Therefore, in this paper, we study the validity through simulation modeling related to linkage analysis according to system topology.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.7
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• pp.26-36
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• 2014

The needs of active phased arrays antenna system is getting more increased for IMT-Advanced system efficiency. The active phased array structure consists of lots of small transceivers and radiation elements to increase system efficiency. The minimized module of high efficiency transceiver is key for system implementation. The power amplifier of transmitter decides efficiency of base-station. In this paper, we design and implement minimized module of high efficiency transceiver for IMT-Advanced active phased array system. The temperature compensation circuit of transceiver reduces gain error and the analog pre-distorter of linearizer reduces implemented size. For minimal size and high efficiency, the implented power amplifier consist of GaN MMIC Doherty structure. The size of implemented module is $40mm{\times}90mm{\times}50mm$ and output power is 47.65 dBm at LTE band 7. The efficiency of power amplifier is 40.7% efficiency and ACLR compensation of linearizer is above 12dB at operating power level, 37dBm. The noise figure of transceiver is under 1.28 dB and amplitude error and phase error on 6 bit control is 0.38 dB and 2.77 degree respectively.

• Journal of Sensor Science and Technology
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• v.6 no.5
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• pp.385-391
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• 1997

An objection of this study is to develop a measuring circuit of a gauge using radioisotope for compaction control. The gauge developed in this study makes use of radioisotope with the activity exempted from domestic atomic law and consists of measuring circuits for gamma-rays and thermal neutrons, a high voltage supply unit, and a microprocessor. To obtain meaningful numbers of pulse counts, parallel five and two circuits are provided for gamma-rays and thermal neutrons, respectively. Being simple in electrical characteristics of G-M detector for gamma-rays, pulses are counted through only a shaping circuit. Very small pulses generated from He- 3 proportional detector for thermal neutrons are amplified to the maximum of 50 [dB] and a window comparator accepts only pulses with meaning. To minimize effects of natural environmental radiation and electrical noise, circuits are electrostatically shielded and pulses made by ripples are eliminated by taking frequency of high voltage supplied to the circuit and pulse height of ripples into consideration. One-chip microprocessor is applied to process various counts, results are stored and the gauage is made capable to communicate with PC. Enough and meaningful numbers of pulses are counted with the prototype gauage for compaction control.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.320-329
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• 2021

In this paper, an empirical model of air bubble size to be applied to an air masker for reduction of underwater radiation noise is presented. The proposed model improves the divergence problem under the low-speed flow condition of the existing model derived using Rayleigh's jet instability model and simple continuity condition by introducing a jet flow velocity of air. The jet flow velocity of air is estimated using the bubble size where the liquid is quiescent. In a medium without flow, the size of the bubble is estimated by an empirical method where bubble formation regime is divided into a laminar-flow range, a transition range, and a turbulent-flow range based on the Reynolds number of the injected air. The proposed bubble size model is confirmed to be in good agreement with the Computational Fluid Dynamics (CFD) analysis result and the experimental results of the existing literature. Using the acoustic inversion method, the air bubble population is estimated from the insertion loss measured during the air injection experiment of the air- masker model in a large cavitation tunnel. The results of the experiments and the bubble size model are compared in the paper.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.97-105
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• 2020

Recently, as the data speed and operating frequencies of Ethernet keeps increasing, electro magnetic interference (EMI) also becomes increasing. The generation of such EMI will cause malfunction of near electronic devices. In this study, EMI filters were applied to reduce the EMI generated by DC-DC SMPS (switching mode power supply), which is the main cause of EMI generation of Ethernet switch. As the EMI filter, MLCCs with excellent withstanding voltage characteristics were used, which had advantages in miniaturization and mass production. Two types of EMI MLCC filters were used, which are X-capacitor and X, Y-capacitor. X-capacitor was composed of 2 MLCCs with 10 nF and 100 nF capacity and 1 Mylar capacitor. Y-capacitor was consisted of 6 MLCCs with a capacity of 27 nF. When only X-capacitor was applied as EMI filter, the conductive EMI field strength exceeded the allowable limit in frequency range of 150 kHz ~ 30 MHz. The radiative EMI also showed high EMI strength and very small allowable margin at the specific frequencies. When the X and Y-capacitors were applied, the conductive EMI was greatly reduced, and the radiation EMI was also found to have sufficient margin. In addition, X, Y-capacitors showed very high insulation resistance and withstanding resistance performances. In conclusion, EMI X, Y-capacitors using MLCCs reduced the EMI noise effectively and showed excellent electrical reliability.

• Journal of the Korean Society of Radiology
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• v.16 no.1
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• pp.7-13
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• 2022

This study compared the aortic root image by using the ECG gating and non-ECG gating methods. We observed the presence or absence of progression of the aortic root image in the images examined by the high pitch (flash) chest pain protocol method and in the patients tested without ECG gating by the conventional method. The AAPM phantom was scanned by using high pitch (flash) chest pain protocol and general chest pain protocol. CTDI values were compared. By ECG gating, the blurring of ascending aorta was significantly reduced compared to the existing non-ECG gating test method, and the image quality of the aortic root was improved. Within the parametar range that did not show differences in noise, uniformity, and high contrast resolution, CTDI values were lower when tested with the high-pitch chest pain protocol. It was found that there is an advantage in dose reduction, and if it is applied and applied to diagnostic fields such as dissection using the dose reduction mode in the cardiac field, it is a very important test for patients who need rapid diagnosis and prompt treatment as well as a dramatic reduction in exposure dose. It is presumed to be a method.

• Journal of the Korean Society of Radiology
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• v.5 no.2
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• pp.93-96
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• 2011

Currently, the development of direct conversion radiation detector using photoconductor materials is progressing in widely. Among of theses photoconductor materials, mercuric iodide compound than amorphous selenium has excellent absorption and sensitivity of high energy radiation. Also, the detection efficiency of signal generated in photoconductor film varies by electric filed and geometric distribution according to top-bottom electrode size. Therefore, in this work, the x-ray detection characteristics are investigated about the size of top electrode in $HgI_2$ photoconductor film. For sample fabrication, to solve the problem that is difficult to make a large area film, we used the spatial paste screen-print method. And the sample thickness is $150{\mu}m$ and an film area size is $3cm{\times}3cm$ on ITO-coated glass substrate. ITO(Indium-Tin-Oxide) electrode was used as top electrode using a magnetron sputtering system and each area is $3cm{\times}3cm$, $2cm{\times}2cm$ and $1cm{\times}1cm$. From experimental measurement, the dark current, sensitivity and SNR of the $HgI_2$ film are obtained from I-V test. From the experimental results, it shows that the sensitivity increases in accordance with the area of the electrode but the SNR is decreased because of the high dark current. Therefore, the optimized size of electrode is importance for the development of photoconductor based x-ray imaging detector.

• Journal of radiological science and technology
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• v.38 no.3
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• pp.245-252
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• 2015

To obtain the best SNR (signal to noise ratio) due to changes in CTDI (computed tomography dose index) made for the purpose of setting the optimum image obtained by reducing the dose in abdominal CT. Abdominal CT scans of 59 patients a $400-499cm^2$ (n = 12), $500-599cm^2$ (n = 21), $600-699cm^2$ (n = 17), $700-799cm^2$ (n = 9) were separated by four groups and the effective dose was used in the Excel to get the area of the patient using the ImageJ program. Patients of CTDI, DLP, SNR, the effective dose were analyzed. Abdominal CT area was increased to 13 mGy in CTDI is 7.3 mGy, DLP to 732 in $394.4mGy{\cdot}cm$, also effective dose was 5.9 mSv increase in 11mSv. SNR is 15 dB was maintained at 12.7. CTDI according to the average of the abdominal area of 8.9 mGy, the average of the DLP was $481.54mGy{\cdot}cm$, the effective dose is calculated to be 7.2 mSV. Effective dose was calculated by multiplying the load factor of DLP in the abdomen showed no statistically significant difference of (p < .05), there was a significant difference in SNR (p > . 05). To improve image quality of abdominal CT scan image in consideration of the CTDI according to the volume of the patient it should be able to reduce the radiation exposure of the patients.