• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.131-134
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• 2003

We demonstrated an optical frequency synthesizer based on a femtosecond (fs) mode-locked Ti:sapphire (Ti:s) laser by simultaneously stabilizing the carrier-offset frequency, $f_{ceo}$, and repetition rate, $f_{ rep}$, referenced to the Cs atomic frequency standard. By using two wide-band digital phase-detectors we realized a phase-coherent link between $f_{rep} and f_{ceo} with the relation f_{ceo} = f_{AOM} 5/6f_{rep} ≡ 0, where f_{AOM} = 5/6f_{rep}$ is the phase-locked driving frequency of an acousto-optic modulator (AOM) in a self-referencing interferometer and $f_{rep}$ = 100 MHz. As a result, we could stabilize all components of the fs laser comb at once with an equal frequency separation $f_{rep}$ = 100 MHz with $f_{ceo}$ = 0. In our optical frequency synthesizer, the frequency of the nth component ($f_{n}$) is given exactly by the simple relation $f_n = nf_{rep}$, enabling us to use the fs laser comb as a frequency ruler in the optical frequency metrology.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.77-80
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• 2003

We design the local oscillator system of the 100 GHz band radio receiving system for a cosmic radio observation. We use the YIG oscillator with digital driver which is the main oscillator. This oscillator has a good frequency and phase stability at some temperature variation, and the easy computer aided control characteristics. This total system designed to two subsystem, first is the oscillator system include YIG oscillator, tripler, harmonic mixer and triplexer etc., second is the PLL system to supply the precise and stable local oscillator frequency to mixer. The proposed local oscillator system in this paper can be use a single or multi pixel receiver because this system can be lock the local oscillator frequency automatically using PC.

• 소음진동
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• 제4권4호
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• pp.443-449
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• 1994

In the analysis of circular cylindrical shell's vibration and sound radiation, there are numerical and analytical methods. Numerical methods such as F.E.M and B.E.M, have the limit of frequency range. Analytical method can be applied to the circular cylindrical shell from low frequency to high frequency. In this paper, we use the analytical method for shell, and numerical method, F.D.M, for fluid. We also use the method using transfer matrix and eigenanalysis of transfer matrix which can therefore calculate the rotational d.o.f that is very imkportant in synthesis with inner structure. Inner structure has much effect on the submerged circular cylindrical shell vibration and sound rediation. Results for the immersed circular cylindrical shell vibration and sound radiation are compared with the analytic solutions.

• 소음진동
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• 제7권4호
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• pp.579-588
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• 1997

When a membrane couples with compressive fluid, waves on the membrane follow a typical dispersion relations. One of characteristics of this relations is that evanscent waves occur below cutoff frequency. We have attempt to use this spatially decaying characteristics as a low frequency sound absorber. Theoretical development has required to solve membrane-fluid coupled linear differential. The solution has been successfully obtained by using eigenfunctions. To assure the obtained solution, experiment was also performed. The comparison was quite satisfactory. We conclude, based on these theoretical as well as experimental evidences, that it is very likely possible to use a membrane as a low frquency sound control element.

• Journal of Electrical Engineering and Technology
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• 제1권4호
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• pp.534-542
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• 2006

This paper presents results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation, their analyses and use of the data for modeling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responses were parameterized with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarization mechanisms and they were thereafter used to model the FRA response of a three-phase transformer.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.87-90
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• 1995

When the ultrasonic transducer operating at l MHz for use in cleaning semiconductor wafers or other industsrial materials is driven from the MOS-FET DC-to RF inverter, the output power severely depends on the frequency of operation since the quality factor of the transducer is high. In order to tune to the eresonating frequency of the ultrasonic transducer, the drive signal frequency of the MOS-FET power inverter is automatically scananed until the frequency is set at the resonating frequency of the ultrasonic transducer is maximized. The control circuit consists of an output power sensing circuit, a PLL controller, a frequency standard, and other peripheral circuits. The operation was satisfactory when the transducer having an output of 600 W at 1 MHz was used.

• 한국통신학회논문지
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• 제19권10호
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• pp.1872-1879
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• 1994

Ku-Band주파수 합성기를 PLL과 주파수 체배 방법을 이용하여 설계 및 제작하였다. 안정된 약 1 GHz의 주파수를 합성하기 위해 PLL 회로의 설계 과정 및 동작 특성을 제어이론을 바탕으로 고찰하였다. 안정된 약 1 GHz PLL 회로에 주파수 2 체배기, 주파수 8 체배기를 연결하여 Ku-Band 주파수를 합성하였다. 실험결과를 통하여 Ku-Band 주파수 합성기 설계 방법의 타당성을 확인하였다.

• 전력전자학회논문지
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• 제25권5호
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• pp.404-411
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• 2020

Inductive power transfer (IPT) systems for electric vehicles generally require zero phase angle (ZPA) frequency tracking control to achieve high efficiency. Current sensors are used for ZPA frequency tracking control. However, the use of current sensors causes several problems, such as switching noise, degrading control performance, and control complexity. To solve these problems, this study proposes ZPA frequency tracking control without current sensors. Such control enables ZPA frequency tracking without real-time control and achieves stable zero voltage switching operation closed to ZPA frequency within all coupling coefficient and load ranges. The validity of the proposed control algorithm is verified on LCCL-S topology with a 3.3 kW rating IPT experimental test bed. Simulation verification is also performed.

• 대한의용생체공학회:의공학회지
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• 제16권2호
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• pp.183-190
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• 1995

The use of ultrasound pulsed Doppler systems has become increasingly popular due to the advantages of easy measurements of blood velocity, volume blood blow, and irregularities of the circulatory system. However, the 2-D Doppler systems have several problems, such as range ambiguity, low signal to noise ratio, and slow frame rate. The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in pulsed Doppler systems. A conventional approach to resolve this problem is tracking the mean frequency close to and beyond the Nyquist frequency along the temporal axis. In this paper, a new concept of tracking the mean frequency along the spatial axis is proposed. The proposed technique is fault tolerant by nature and more suitable for multi gate and 2-D Doppler system than conventional methods.

• 대한영양사협회학술지
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• 제13권1호
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• pp.73-83
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• 2007

In order to investigate the ecological factors affecting milk intake frequency of adolescents, the questionnaire survey was conducted with 929 middle and high school students living in Chungnam urban area through October and November 2004. The subjects consumed milk 8.6$\pm$6.7 times per week, other beverages 4.4$\pm$4.1 times per week and drinking water 3.7$\pm$2.1 cups per day. Of the students 77.3% took balanced meals, 72.8% ate regularly and 36.2% ate adequate amount. About 61% had breakfast everyday and nearly a half students snacked once a day. Nutritional knowledge scores about milk was 7.2$\pm$1.7 and milk attitude scores was 28.1$\pm$6.5. The subjects spent daily 1.8$\pm$1.1, 1.9$\pm$1.1, and 1.0$\pm$0.5 hours for computer use, TV watching and exercise, respectively. Milk intake frequencies were positively correlated with excercise, snack frequency, meal balance and regularity, breakfast frequency, food attitude score and milk preference, while showed negative correlationships with TV watching and computer use. Intake frequency of fruit-tasted and chocolate milk showed inverse correlation with nutritional knowledge. Subjects without either school store or vending machine took milk more frequently than those with one or both did. Of the correlated variables, milk preference was the most important influencing factor to milk intake frequency according to the stepwise linear regression analysis, which presented other 5 important influencing factors as food attitude, school vending facilities, excercise, snacking frequency and watching TV. In conclusion, the improvement of milk preference is the most important and effective way to promote milk consumption in adolescents. The favorite ways of drinking milk, nutritional benefit of milk, healthy beverage and good snacking should be taught in nutrition education. Also physical activities should be recommended to students rather than watching TV, computer use and vending facilities selling soft drinks should be limited to be established inside school.