• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.9
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• pp.987-994
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• 2010

In this paper, a simple and effective active load-pull method is proposed, and the method to improve the efficiency of X-band power amplifier using harmonic control circuit is presented. The proposed active load-pull system mainly consists of directional coupler, phase shifter, short circuit, and power amplifier, and allows a user to access reflection coefficients near the edge of the Smith chart($\Gamma$=1) easily. The device used in this paper is Mitsubishi's GaAs FET MGF1801, and the operating frequency of the power amplifier is 9 GHz, The amplifier had output power of 21.65 dBm and drain efficiency of 24.9 % at class-A, and had output power of 21.46 dBm and drain efficiency of 53.3 % at class-AB. Harmonic control circuit is designed only second and third harmonic components because of the bandwidth limitation of the microwave components. The drain efficiency is improved as much as 6.4 % compared with class-AB power amplifier.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.443-451
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• 2010

This paper describes a fully integrated CMOS low-IF mobile-TV RF tuner for Band-III T-DMB/DAB applications. All functional blocks such as low noise amplifier, mixers, variable gain amplifiers, channel filter, phase locked loop, voltage controlled oscillator and PLL loop filter are integrated. The gain of LNA can be controlled from -10 dB to +15 dB with 4-step resolutions. This provides a high signal-to-noise ratio and high linearity performance at a certain power level of RF input because LNA has a small gain variance. For further improving the linearity and noise performance we have proposed the RF VGA exploiting Schmoock's technique and the mixer with current bleeding, which injects directly the charges to the transconductance stage. The chip is fabricated in a 0.18 um mixed signal CMOS process. The measured gain range of the receiver is -25~+88 dB, the overall noise figure(NF) is 4.02~5.13 dB over the whole T-DMB band of 174~240 MHz, and the measured IIP3 is +2.3 dBm at low gain mode. The tuner rejects the image signal over maximum 63.4 dB. The power consumption is 54 mW at 1.8 V supply voltage. The chip area is $3.0{\times}2.5mm^2$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.362-370
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• 2010

In this paper, a compact RF Front-end module for Wireless Fidelity(Wi-Fi) and Worldwide Interoperability for Microwave Access(WiMAX) applications is realized by low temperature co-fired ceramic(LTCC) technology. The RF Front-end module is composed of three LTCC band-pass filters, a Film Bulk Acoustic Resonator(FBAR) filter, fully embedded matching circuits, an SPDT switch for mode selection, an SPDT switch for Tx/Rx selection, and an SP4T switch for band selection. The parasitic elements of 0.2~0.3 pF are generated by the structure of stacking in the top pad pattern for DC block capacitor of SPDT switch for mode selection. These kinds of parasitic elements break the matching characteristic, and thus, the overall electrical performance of the module is degraded. In order to compensate it, we insert a parallel lumped-element inductor on capacitor pad pattern for DC block, so that we obtain the optimized performance of the RF Front-end module. The fabricated RF front-end module has 12 layers including three inner grounds and it occupies less than $6.0mm{\times}6.0mm{\times}0.728mm$.

• Journal of Environmental Health Sciences
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• v.43 no.2
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• pp.103-110
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• 2017

Objectives: This study was performed to provide basic data for the re-establishment of standards (criteria) and analytical methods for hazardous metals in nail enamel. Methods: Ten metals (lead; Pb, arsenic; As, cadminum; Cd, antimony: Sb, cobalt; Co, nikel; Ni, copper; Cu, chromium; Cr, aluminum; Al, and mercury; Hg) were measured in 67 commercial nail enamels containing glitter and/or pearls. The content of hazardous metals (excepting Hg) was determined by using an inductively coupled plasma-optical emission spectrophotometer (ICP-OES) after microwave digestion. Mercury content was measured by a mercury analyzer without any preparation. Results: The detected ranges of the intact samples were as follows: $ND-1.756{\mu}g/g$ for Pb, $ND-1.24{\mu}g/g$ for As, ND for Cd, $ND-20.41{\mu}g/g$ for Sb, $ND-12.36{\mu}g/g$ for Co, $ND-7.908{\mu}g/g$ for Ni, $0.088-79.27{\mu}g/g$ for Cu, $0.281-18.54{\mu}g/g$ for Cr, $13.78-3563{\mu}g/g$ for Al, and $ND-0.044{\mu}g/g$ for Hg. After centrifugation, the detected ranges of supernatant were as follows: $ND-0.435{\mu}g/g$ for Pb, $ND-0.504{\mu}g/g$ for As, ND for Cd, $ND-0.035{\mu}g/g$ for Sb, $ND-13.17{\mu}g/g$ for Co, $ND-0.232{\mu}g/g$ for Ni, $0.117-90.07{\mu}g/g$ for Cu, $0.174-2.787{\mu}g/g$ for Cr, and $9.459-1565{\mu}g/g$ for Al. The results of this analysis showed that the levels of heavy metals such as Pb, As, and Sb were much higher in the intact samples than those of supernatant. Conclusion: In the present study, we found that the levels of hazardous metals were significantly different depending on the status of the presence of glitter. Based on the results, we recommend that the product consumer refrain from prolonged application of nail enamel, avoid biting or chewing the nails, and wear gloves during cooking and washing dishes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.99-104
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• 2020

In this study, we fabricated a metamorphic high-electron-mobility transistor (mHEMT) device with a T-type gate structure for the implementation of W-band monolithic microwave integrated circuits (MMICs) and investigated its characteristics. To fabricate the mHEMT device, a recess process for etching of its Schottky layer was applied before gate metal deposition, and an e-beam lithography using a triple photoresist film for the T-gate structure was employed. We measured DC and RF characteristics of the fabricated device to verify the characteristics that can be used in W-band MMIC design. The mHEMT device exhibited DC characteristics such as a drain current density of 747 mA/mm, maximum transconductance of 1.354 S/mm, and pinch-off voltage of -0.42 V. Concerning the frequency characteristics, the device showed a cutoff frequency of 215 GHz and maximum oscillation frequency of 260 GHz, which provide sufficient performance for W-band MMIC design and fabrication. In addition, active and passive modeling was performed and its accuracy was evaluated by comparing the measured results. The developed mHEMT and device models could be used for the fabrication of W-band MMICs.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.6
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• pp.864-869
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• 2003

In order to expand the acceptability of irradiated foods by public, substantial basic data about the change of nutrient contents during irradiation are needed. The nutrient contents and digestibility of macronutrients such as carbohydrates, proteins and lipids in foods are known to be not significantly influenced by irradiation treatment. However, some of the vitamins among micronutrients are susceptible to irradiation to a large extent depending upon the food composition, food process and storage condition. This study was conducted to investigate change of thiamin in chicken breast, and vitamin C in strawberry and mandarine orange after irradiation. The effects of irradiation at frozen or refrigerated state and the effects of cooking such as heating or micron ave on thiamin contents in chicken breast were observed. Irradiation reduced the thiamin content, however, temperature condition during irradiation was much more important factor to the loss of thiamin contents. In strawberry, vitamin C content was significantly affected by original content or the variety rattler than treatments such as irradiation, heating or microwave. These results indicated that the losses of water-soluble vitamins, especially thiamin or vitamin C, are affected by food temperature during irradiation process and variety or composition of foods rallier than irradiation itself, within an acceptable range of irradiation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.45 no.8
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• pp.1221-1226
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• 2016

This study investigated changes in the S-allyl-L-cysteine (SAC) content of garlic using different cooking methods. Methods for determining SAC were validated by determining specificity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy using an high-performance liquid chromatography-fluorescence detection system. Results showed high linearity in the calibration curve with a coefficient of correlation ($R^2$) of 0.9999. The LOD and LOQ values for SAC were 0.15 and $0.47{\mu}g/mL$, respectively. The relative standard deviations for intra- and inter-day precision of SAC were less than 5%. The recovery rate of SAC was in the range from 97.35% to 97.47%. The SAC content of raw garlic was 2.77 mg/g, and there was no significant difference in SAC content according to blanching and microwave treatment. However, SAC content upon boiling and autoclaving at $110^{\circ}C$ and $121^{\circ}C$ increased from 3.50~9.16 mg/g, 6.52~16.21 mg/g, and 14.15~50.24 mg/g with increasing cooking temperature and time, respectively.

• Journal of Advanced Navigation Technology
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• v.22 no.5
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• pp.442-448
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• 2018

In this paper, a microstrip antenna for LTE / LTE-A is designed and fabricated for a broadband mobile communication system. The proposed antenna is designed to have the characteristics of using FR-4 (er = 4.3), size of $40mm{\times}50mm$, and LTE / LTE-A frequency bands of 2.3 GHz and 2.5 GHz. 2014, and the simulation result shows that the gain is 2.391 dBi at 2.3 GHz and 2.566 dBi at 2.5 GHz. The S-parameter also showed a result of less than -10 dB (WSWR 2: 1) in the desired frequency band. The broadband mobile communication antenna has been miniaturized, high performance, and light weight, and an excellent and low cost system is continuously being developed, and a broadband mobile communication system is used by many people. Since LTE / LTE-A technology has been proposed according to the development of system and demand, it is expected that many users will design and manufacture antennas satisfying the above conditions and apply the applied technology.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.85-85
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• 2011

홍수기에 안전하고 정확한 유량측정을 통하여 물관리에 필요한 기초수문자료를 확보하고자 한국수자원공사에서 1993년도부터 홍수유량측정기술 확보를 위한 연구를 시작하였다. 그간의 연구성과를 바탕으로 1999년도에 하천의 유속을 비접촉식으로 측정할 수 있는 홍수용 전자파표면유속계를 개발하여 특허등록하였고 그와 동시에 이의 상품화를 추진하여 2010년도까지 75대를 보급하여 실무에서 이용하고 있다. 이동식인 홍수용 전자파표면유속계를 바탕으로 2001년도에는 고정식 실시간 홍수유량측정측정시스템을 개발하여 특허등록하였고, 이 시제품을 현재 용담 수자원시험유역의 동향지점에서 시험운영하고 있다. 또한, 현장 유량측정실무자들의 홍수용 전자파표면유속계 개선요구에 따라 편각용 전자파표면유속계 시제품을 개발하였으며, 이는 임의의 한 지점에 설치한 한 대의 장비로 좌우 여러 측선의 유속을 동시에 측정할 수 있는 다점 측정기능을 갖도록 성능을 개선하였다. 이에 따라 홍수시 유량측정에 소요되는 시간이 줄어들어 신속하게 유량측정을 완료할 수 있는 계기를 마련하였다. 이와 더불어 유속측정 범위를 확장하여 홍수시의 고유속 뿐만 아니라 0.5 m/s 이하의 저유속까지 측정할 수 있는 범용 전자파표면유속계의 시제품을 추가로 개발하였다. 이 장비는 최저유속 0.03 m/s의 측정을 실내시험을 통하여 입증하였다. 범용 전자파표면유속계는 상품화 시제품의 개발을 목표로 기존 시제품의 현장시험을 통하여 현장적용상의 문제점에 대한 해결에 주력하였다. 첫째, 평갈수용 전자파표면유속계의 사용편의를 개선하기 위하여 소형화 및 경량화를 추진하였고, 이를 위하여 사용주파수를 기존의 10 GHz에서 24 GHz로 변경함으로써 $35{\times}35\;cm$ 크기의 기존안테나를 $22{\times}22\;cm$ 크기로 소형화하였으며 송수신부의 무게는 기존 18 kg에서 3.3 kg으로 혁신적으로 줄이는데 성공하였다. 이를 위하여 안테나는 기존의 반사형안테나에서 도파관슬롯배열안테나로 변경하였다. 둘째, 측정값의 안정화를 위하여 안테나의 특성을 개선하여 부엽(side-lobe) 레벨 30 dB 이하 그리고 전후방비(front-back ratio) 50 dB 이하로 개선하여 안테나가 지향하는 방향 이외의 위치에서 반사되는 불필요한 신호를 줄였다. 또한 적응형 이득제어(adaptive gain control)기법의 채택으로 미소 신호에 대한 안정적 측정 및 과다 신호에 대한 능동적 감쇄를 할 수 있도록 시스템을 구성하여 전 유속범위에 대한 안정적 측정을 가능토록 설계 및 제작하였다. 셋째, 자가점검 기능을 탑재하여 유속측정 전에 기기의 상태에 대한 self test기능을 통하여 측정자가 기기의 상태를 사전에 파악 가능토록함으로써, 기기 오작동에 대한 능동 대처할 수 있도록 하였다. 이외에도 저전력 회로설계를 통하여 배터리 사용시간을 확장하였고, 기존의 전자파표면유속계가 가지고 있던 방습 및 방수에도 내성을 갖는 제품으로 설계하였으며 스마트기기를 이용한 무선측정 및 세련된 디자인 등 사용자의 요구사항을 충분히 반영하였다.

• Journal of Food Hygiene and Safety
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• v.12 no.3
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• pp.240-253
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• 1997

The main problems contributing to food poisoning outbreaks in institutional settings and a home were reviewed and analyzed through the epidemiological investigations of food poisoning. The major documented factors included improper holding temperatures, inadequate cooking, poor personal hygiene, cross-contamination and contaminated equipment, food from unsafe sources, failure to follow food hygiene policies, and lack of education, training, monitoring and superivision. Usually more than one factor contributed to the development of an outbreak. (1) Use of improper holding temperatures was the single most important factor contributing to food poisoning. They included improper cooling, allowing a laps of time (12 hours or more) between preparing food and eating it, improper hot holding, and inadequate or improper thawing. Food thermometers were not used in most of the instances. (2) In inadequate cooking, the core temperature of food during and after cooking had not been measured, and routine monitoring was limited to recording the temperature of plated meals. Compared with conventional methods of cooking, microwave ovens did not protect against food poisoning as effectively. Centralized food preparation potentially increased the risk of food poisoning outbreaks. (3) Poor personal hygiene both at the individual level (improper handwashing and lack of proper hygienic practices) and at the institutional level (poor general sanitization) increased the risk of transmission. Person to person transmission of enteric pathogens through direct contact and via fomites has been noted in several instances. (4) Obtaining food from unsafe sources was a risk factor in outbreaks of food poisoning. Food risks were high when food was grown or harvested from contaminated areas. Possibilities included contamination in the field, in transport, at the retail site, or at the time it was prepared for serving. (5) Cross-contamination and inadequate cleaning/handling of equipment became potential vehicles of food poisoning. Failure to separate cooked food from raw food was also a risk factor. (6) Failure to follow food hygiene policies also provided opportunities for outbreaks of food poisoning. It included improper hygienic practices during food preparation, neglect of personnel policies (involvement of symptomatic workers in food preparation), poor results on routine inspections, and disregarding the results and recommendations of an inspection. (7) Lack of formal and in-service education, training, monitoring, and supervision of food handlers or supervisors were critical and perhaps neglected elements in occurrences of food poisoning.