• Current Optics and Photonics
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• v.5 no.3
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• pp.289-297
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• 2021

We describe a comb-mode resolving spectroscopic technique by direct time-domain phase correction of unstable interferograms obtained from loosely locked two femtosecond lasers. A low-cost continuous wave laser and conventional repetition rate stabilization method were exploited for locking carrier and envelope phase of interferograms, respectively. We intentionally set the servo control at low bandwidth, resulting in severe interferograms' fluctuation to demonstrate the capability of the proposed correction method. The envelope phase of each interferogram was estimated by a quadratic fit of carrier peaks to correct timing fluctuation of interferograms in the time domain. After envelope phase correction on individual interferograms, we successfully demonstrated 1 Hz linewidth of RF comb-mode over 200 GHz optical spectral-bandwidth with 10-times signal-to-noise ratio (SNR) enhancement compared to the spectrum without correction. Besides, the group delay difference between two femtosecond pulses is successfully estimated through a linear slope of phase information.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.3
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• pp.262-271
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• 2002

In PWM inverters used in traction motor drive systems, the switching frequency is restricted by their large power capacity and thus the electromagnetic acoustic noise is generated. To reduce such an audible noise, the new MRSF-PWM(Modified Random Switching Frequency PWM) method is proposed. In the Proposed MRSF-PWM method, both triangular wave and sawtooth wave are used together as carrier waves for harmonic diffusion and reference wave is generated by injecting 3rd harmonic into the stone wave to expand the linear control region of output voltages. To verify the validity of the proposed MRSF-PWM method, computer simulations are carried out. And the results show that the MRSF-PWM method is more excellent than other RPWM methods in the aspects of both linearity and harmonic diffusion md more effective than SPWM(Sinusoidal PWM) method for the reduction of an audible noise.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.57-61
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• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.53-60
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• 2020

In liquid-fuel spray combustion, an experimental study was conducted to observe the effect of ultrasonic excitation on the ultrasonically-atomized liquid fuel flame by controlling pressure field through an ultrasonic standing wave. Flame of the ultrasonically-atomized kerosene aerosol was visualized by using a high speed camera, DSLR, and Schlieren photography. The amount of fuel consumed was obtained by a precise flow-rate measurement technique during combustion, through which the ratio of carrier gas (air) to fuel mass was able to be obtained, too. As a result, it could be found that the combustion reaction-rate of the liquid-fuel aerosol was increased by applying an ultrasonic standing wave to the secondary flame zone of the flame.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2023.11a
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• pp.116-118
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• 2023

In recent years, the need for economical and sustainable ship routing has emerged due to the enforced regulations on environmental issues. Despite the development of weather forecasting technology, maritime accidents by rough waves have continued to occur due to incorrect weather forecasts. In this study, onboard measurements are conducted to observe the acutal situation on merchant ships in operation encountering rough waves. The types of measured data include information related to navigation (Ship's position, speed, bearing, rudder angle) and engine (engine revolutions, power, shaft thrust, fuel consumption), weather conditions (wind, waves), and ship motions (roll, pitch, and yaw). These ship experiments was conducted to 28,000 DWT bulk carrier, 63,000 DWT bulk carrier, 20,000 TEU container ship, and 12,000 TEU container ship. The actual ship experiment of each ship is intended to acquire various types of data and utilize them for multi-objective studies related to ship operation. Additionally, in order to confirm the sea conditions, the directional wave spectrum was reproduced using a wave simulation model. Through data collection from ship experiments and wave simulations, various studies could be proceeding such as the measurement for accurate wave information by marine radar and analysis for cargo collapse accidents. In addition, it is expected to be utilized in various themes from the perspective of safety and efficiency in ship operation.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1984.04a
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• pp.33-36
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• 1984

An underwater communication technic using AM modulated ultrasonicwave was studied. The experiment were performed in the ahechoic water tank with 60KHz carrier wave and the frequency response of the system by demodulated signals were measured varing the degree of modulation and distance between transmitter and receiver. The bandwidth of transmitted signals was limited by the acoustic characteristics. As the result, it was found out that this kind of system is applicable to the underwater speech communication.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.178-179
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• 2001

무선 통신망의 수요가 급격히 증가하여 기존의 무선통신 대역이 조만간에 포화될 것으로 예측됨에 따라, 새로운 밀리메터파 대역 통신에 대한 연구 관심이 높아지고 있다. 광 밀리메터파 발생 및 전송 시스템은 밀리메터 반송파 발생이 용이할 뿐만 아니라 밀리메터파 광중계기 구현에 그대로 적용되기 때문에, 차세대 밀리메터파 통신 시스템 구현의 핵심기술로서 연구관심의 대상이 되어왔다. 광 밀리메터파 발생 방법으로는 두 개의 레이저를 이용하는 광파 혼합과 외부 변조기로 직접변조하는 방법 등이 있다. (중략)

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.271-272
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• 2007

Displacement current $(I_{dis})$ and drain-to-source current $(I_{DS})$ are evaluated using the simultaneous measurements of source $(I_S)$ and drain $(I_D)$ currents during the application of a constant drain voltage and a triangular-wave gate voltage $(V_{GS})$ to top-contact pentacene thin-film transistors.

• 전기의세계
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• v.16 no.1
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• pp.14-18
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• 1967

To analyze th frequency modulation system the characteristic equation of the F-M system, i.e., Mathieu's equation, is derived from the equivalent circuits of direct modulation system. The analysis of F-M equation is undertaken by the Yonsei 101 Analog Computer. And the computer solution is compared with the theoretical solution. It is concluded that not only the frequency but also the amplitude of the carrier wave are changed by varying the modulation index and the system becomes unstable if the modulation index is increased near to unity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.271-277
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• 2004

A Si(Silicon) MEMS(Micro Electro Mechanical System) package using a doped lossy Si carrier for CPW(Coplanar Waveguide) MMICs(Microwave and Millimeter-wave Integrated Circuits) is proposed in order to reduce parasitic problems of leakage, coupling and resonance. The proposed chip-carrier scheme is verified by fabricating and measuring a GaAs CPW on the two types of carriers(conductor-back metal, doped lossy Si) in the frequency from 0.5 to 40 ㎓. The proposed MEMS package using the lightly doped lossy(15 Ω$.$cm) Si chip-carrier and the HRS(High Resistivity Silicon, 15 ㏀$.$cm) shows the optimized loss and parasitic problems-free since the doped lossy Si-carrier effectively absorbs and suppresses the resonant leakage. The Si MEMS package for CPW MMICs has an insertion loss of only - 2.0 ㏈ and a power loss of - 7.5 ㏈ at 40 ㎓.