• Current Optics and Photonics
• /
• 제5권3호
• /
• pp.289-297
• /
• 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.

• 한국군사과학기술학회지
• /
• 제10권2호
• /
• pp.160-169
• /
• 2007

In this paper, we have described and simulated the effect analysis and correction of phase errors in the SAR rawdata induced by satellite attitude errors such as drift, jitter. This simulation is based on the FSA(Frequency Scaling Algorithm) for high resolution image formation of the Spotlight SAR. Phase errors produce the degradation of SAR image quality such as loss of resolution, geometric distortion, loss of contrast, spurious targets, and decrease in SNR. To resolve this problem, this paper presents method for correction of phase errors using the PGA(Phase Gradient Algorithm) in connection with the FSA. Several results of the phase errors correction are presented for Spotlight SAR rawdata.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제15권6호
• /
• pp.629-633
• /
• 2015

An active balun using current steering for phase correction is presented. The proposed active balun is constructed with two different unit balun structures based on current steering to reduce phase and amplitude errors. This type of topology can be compared with the conventional phase and amplitude correction techniques which do not incorporate the current steering. Designed and fabricated active balun in $0.18{\mu}m$ CMOS process operates over 0.95 - 1.45 GHz band, showing input reflection coefficient under -15 dB, phase error of $11^{\circ}$ and gain error of 0.5 dB. Gain is measured to be 0.3 dB maximum and power consumption of 7.2 mW is measured.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2006년도 추계학술대회
• /
• pp.241-244
• /
• 2006

The present paper describes the scale effect correction method for wind turbine by using CFD(computational fluid dynamics). For the correct ions of wind turbine scale effect, various researches on the helicopter rotor scale effect were Investigated and feasibility study of methods was performed to correct wind turbine scale effect The present paper also introduces new scale effect correction method based on two dimensional lift slope modification. In order to test the Present method, performance analyses of NREL Phase VI wind turbines under various scale conditions were carried out by using CFD. The present method showed reasonable results when applied to NREL Phase VI wind turbine.

• 한국전자파학회논문지
• /
• 제25권3호
• /
• pp.289-295
• /
• 2014

본 논문에서는 진화된 위상보정 구조를 이용한 0.6~2.0 GHz에서 동작하는 Active Balun을 제안한다. 제안하는 회로는 서로 다른 구조 및 성능을 보이는 Active Balun 회로를 Cascode 구조와 더불어 구현하여 기존의 위상 보정구조를 갖는 회로보다 위상보정에 있어 높은 성능을 보인다. 제안하는 Active Balun은 0.6~2.0 GHz 대역에서 $10^{\circ}$의 위상 오차 및 2dB의 진폭오차를 가지며, 1.8 V DC에서 약 7 mW의 전력을 소모한다.

• 신재생에너지
• /
• 제3권3호
• /
• pp.54-62
• /
• 2007

The present paper describes the scale effect correction methods for scaled NREL Phase VI wind turbines by using CFD[computational fluid dynamics). For the corrections of wind turbine scale effect, various researches on the helicopter rotor scale effect were investigated and the feasibility study of the methods was performed to correct wind turbine scale effect. The present paper also introduces scale effect correction methods based on two dimensional lift slope. In order to test the present method, performance analyses of NREL Phase VI wind turbines under various scale conditions were carried out and new correction method was applied. Granting that the new correction method is valid only above Reynolds No. 100,000, it showed reasonable agreement between model and full scale wind turbines in the linear torque region.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
• /
• pp.663-667
• /
• 1998

This paper describes for reducing harmonic distortion on CO2 welding machine with nonlinear load characteristic using single-switch three-phase AC/DC converter. The low-order harmonic component amplitude of the phase current of single-switch three-phase discontinuous mode is calculated. Experimental results show that CO2 welding machine with single-switch three-phase AC/DC converter is effectively controlled with power factor correction for phase current during welding time.

• ETRI Journal
• /
• 제41권1호
• /
• pp.73-83
• /
• 2019

This paper describes in detail the processing path leading to successful phase images stitching in digital holographic microscope for the extension of the field of view. It applies FIJI Grid/Collection Stitching Plugin, which is a general tool for images stitching, non-specific for phase images. The FIJI plugin is extensively supported by aberration and phase offset correction. Comparative analysis of different aberration correction methods and data processing strategies is presented, together with the critical analysis of their applicability. The proposed processing path provides good background for statistical phase analysis of cell cultures and digital phase pathology.

• Current Optics and Photonics
• /
• 제5권6호
• /
• pp.627-640
• /
• 2021

In a free-space coherent optical communication system, wavefront distortion is frequently beyond the correction range of the adaptive-optics system after the laser has propagated through the atmospheric turbulence. A method of residual wavefront correction is proposed, to improve the quality of coherent optical communication in free space. The relationship between the wavefront phase expanded by Zernike polynomials and the mixing efficiency is derived analytically. The influence of Zernike-polynomial distortion on the bit-error rate (BER) of a phase-modulation system is analyzed. From the theoretical analysis, the BER of the system changes periodically, due to the periodic extension of wavefront distortion. Experimental results show that the BER after correction is reduced from 10^-1 to 10^-4; however, when the closed-loop control algorithm with residual correction is used, the experimental results show that the BER is reduced from 10^-1 to 10^-7.

• Investigative Magnetic Resonance Imaging
• /
• 제15권1호
• /
• pp.57-66
• /
• 2011

목적 : 0.35 Teslas의 저자장 자기공명영상 시스템에서 인체 조직의 물 성분 또는 지방 성분의 영상을 얻는데 있어서 주자장의 불균일도를 two-point Dixon 방법을 기반으로 보정하는 새로운 방법을 모색하였다. 대상 및 방법 : Two-point Dixon 방법을 사용하여 물과 지방의 위상이 동상일 때와 역상일 때의 영상들을 얻은 후 그 영상들로부터 위상과 크기의 위상 크기 결합 밀도 함수를 계산하고, 이를 통해 물과 지방의 영역을 분리하여 3차원 볼륨의 물 영역에서의 주자장의 불균일도 패턴을 분석하고 이를 반복적으로 보정하여 주자장의 불균일도를 개선하였다. 결과 : 제안한 영상 기법으로 인체의 여러 부위에서 주자장의 불균일도를 보정한 물과 지방 영상을 얻을 수 있었다. 삼차원 보정을 통하여 멀티 슬라이스 전체 영상에서 균일하게 물 또는 지방만의 영상을 얻을 수 있었다. 결론 : 위상-크기 결합 밀도 함수를 통하여 물과 지방의 영역을 분리할 수 있었고, 이를 이용하여 자장의 불균일도를 분석하고 보정할 수 있었다. 제안한 방법을 통해 주자장의 불균일도가 월등히 개선된 물 또는 지방 영상을 얻을 수 있었다.