• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.4
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• pp.1-9
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• 2022

In the current study, in order to understand the dynamic response characteristics of the system according to the external acoustic forcing, a numerical approach was developed by adding an sign-sweep forcing function to the existing network model. Through this model, the sensitivity of frequency and pressure amplitude changes according to system parameters such as the physical dimensions and boundary conditions of the target combustor was analyzed in a wide frequency range. Analysis results of dynamic response characteristics of the target combustor are shown that the frequency regime with high dynamic pressure response was similar to the instability frequency range measured in the same combustor, and in particular, the response of the system depends greatly on the location of the acoustic forcing source term.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.229-232
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• 2002

콘서트 홀과 같은 대형 공간의 경우와는 달리, 자동차 내의 작은 공간에서는 저주파의 음향 공진으로 인하여 상대적으로 높은 크로스오버 주파수까지 재생된 사운드가 컬러링 된다. 이러한 크로스오버 주파수는 Schroeder의 'large room limit'로 결정되며, 이것은 작은 공간과 대형 공간을 구분하게 되는 기준이 된다. 이러한 컬러링을 보상하기 위해, 먼저 대역 제한된 사인 스윕 신호를 이용하여 특정 차량의 저주파 응답 범위를 크로스오버 주파수까지 측정하였다. 본 논문에서는 이렇게 측정한 저주파 응답을 이퀄라이징하는 방법에 대하여 논의한다.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.48-49
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• 2003

원자가 전자기파와 상호작용할 때 원자 전이의 결맞음 여기 (coherent excitation of atomic transitions)는 일반적인 현상이다. 이 상호작용은 라비 진동 (Rabi oscillation), 자유 유도 감쇠 (free induction decay), 단열 밀도 이송 (adiabatic population transfer), 결맞음 과도 (coherent transients； CT) 등 다양한 결과를 가져온다. 특히, 전자기파의 주파수가 원자의 공진주파수를 중심으로 스윕될 때 결맞음 과도 현상 (coherent transient phenomenon)은 밀도 반전 (population reversal)을 유도하기도 한다. (중략)

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.299-303
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• 2004

In this paper, it is presented a level sensor for measuring a level of the contents of cargo tank using frequency modulated continuous wave(FMCW). The frequency range is 10∼11 GHz, the radar cross section(RCS) of target is 0.8 ㎡ of metal plate. the experiment is performed in laboratory and open ground, the sweep time of the signal is 100 ms, the pyramidal horn antenna of about 20 dBi gain is used, and input power of antenna is about 5 dBm. the beat frequency according to the target moving to 40 m is measured. There is a good agreement between measured and calculated results. But the resolution of the FMCW radar is measured about 10 cm due to nonlinear of voltage controlled oscillator(VCO).

• Journal of Navigation and Port Research
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• v.28 no.6
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• pp.497-501
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• 2004

In this paper, it is presented a level sensor for measuring a level of the contents of cargo tank using frequency modulated continuous wave(FMCW). The frequency range is 10∼11 GHz, the radar cross section(RCS) of test target is $0.8\textrm{m}^2$ of metal plate. The experiment is performed in laboratory and open ground, the sweep time of the signal is 100 ms, the pyramidal horn antenna of about 22 dBi gain is used, and input power of antenna is about 8 dBm The beat frequency according to the target moving to 40 m is measured. There is a good agreement between measured and calculated results. But the resolution of the FMCW radar is measured about 10 cm due to nonlinear of voltage controlled oscillator(VCO).

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.549-557
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• 2019

The acoustical scattering characteristics of a target are influenced by the material properties and structural characteristics of the target, which are critical information for acoustic detection and identification of underwater target. In particular, for thin elastic target, unique scattered signals are generated around the target by the Lamb wave. In this paper, the results of scattered signal measurement of aluminum spherical shell in the water tank using the stepped frequency sweep sine signal are presented. In particular, the scattering of the water-filled aluminum spherical shell is compared with that of the air-filled one both theoretically and experimentally. The difference of the scattered signals are analyzed using the pseudo Wigner-Ville distribution in terms of average frequency, frequency distribution, and energy of the scattered signal. The result shows that all observed parameters increased when the aluminum sphere was water-filled, and it is well matched to the theoretical expectation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.6
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• pp.35-41
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• 2008

The most important requirement for the automotive radars is the simultaneous target range and velocity measurement under environment of multi-target, clutters, multi-path, and so on. If the many vehicles with 77GHz FMCW(Frequency Modulation Continuous Wave) radar system are in the near area we should consider the interference signals occurred by other radar systems because these signals reduce exact detection of range and velocity. In this paper, we propose the interference cancellation method, which each vehicle radar transmits chirp trains with the different frequency sweep shapes. The proposed method is applied into the various applications such as an intelligent vehicle, Robot, and UGV(Unmanned Ground Vehicle).

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.4
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• pp.22-29
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• 2015

Quadrotor is widely used in variable application nowadays. Due to its inherent unstable characteristics, control system to augment the stability is essential for quadrotor operation. To design control system and verify its performance through simulation, accurate dynamic model is required. Quadrotor dynamic model is simply compared with conventional rotorcraft such as helicopter. However, the accurate dynamic model of quadrotor is not easy to develop because of the highly correlated aerodynamic effect of each rotor. In this paper, quadrotor dynamic model is identified from the flight data using frequency domain approach. Flight test of quadrotor is performed in closed loop configuration with stability augmentation system included. Frequency sweep input is applied in each of lateral, longitudinal, yaw and heave axis separately. The bare dynamic model is identified from the flight data of quadrotor responses and thrust measurement through Pulse Width Modulation(PWM) data. The frequency responses of identified model match well with those of flight data, and time responses of identified model for doublet input in each axis are also shown to agree with flight data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1186-1193
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• 2009

In this paper, we propose DDS(Direct Digital Synthesizer) as a new implementation method of chirp LO(Local Oscillator) for compressive receiver applied for RFID signal detection in UHF band. We designed a receiver whose input frequency range is 908.5~914 MHz, DDL(Dispersive Delay Line) bandwidth is 6 MHz, and dispersion delay time is $13\;{\mu}s$. Chirp LO based on DDS is designed to meet $26\;{\mu}s$ sweep time and 12 MHz bandwidth for complete compressive mechanism. The measured 3 dB pulse width of the compressed signal of the fabricated receiver is 260 ns and the frequency resolution for simultaneous input signals is below 200 kHz. These performances indicate that the proposed chirp LO based on DDS and the compressive receiver is suitable for RFID signal detection in UHF band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.7
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• pp.694-704
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• 2011

In this paper, we present a design of a 5th order Chebyshev interdigital band-pass filter using inverter and susceptance slope parameter values obtained from EM simulated multi-port Y-parameters. The shifted length of the resonator is determined when the frequency of the transmission zero is separated far away from the center frequency. For the initial dimensions of the interdigital filter, the filter is decomposed into the individual resonators, and the dimensions are obtained using EM Simulation of the decomposed resonators. However, the interdigital filter with the dimensions determined from the EM simulation of the decomposed resonators shows slightly distorted response from the desired frequency response due to the coupling between non-adjacent resonators. To obtain a EM simulation dataset, EM simulation for this filter is carried out by parameter sweep with constant ratio for the initial values. In this dataset, it is determined the final values for the filter by optimization. The fabricated filter by PCB shows an upper-shift of center frequency of about 70 MHz, which was caused by permittivity changed and tolerance of fabrication.