• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1461-1465
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• 2010

산업기술의 발전은 자연현상에서 발생되는 다양한 형태의 아날로그 신호를 디지털 신호로 변환할 수 있게 되었으나, 자연현상의 신호는 그 정보량이 상당할 뿐만 아니라 디지털 신호로 변환하는 과정에서 발생되는 계통오차 및 동역학적 노이즈 등이 포함되어 있어 신호 해석에 많은 어려움이 있다. 최근 유량조사 분야에서도 최첨단 유량측정 기술인 초음파 유량계 설치를 통하여 기존의 유량조사 방법으로 불가능했던 감조하천과 대하천에서의 실시간 유량자료를 생산하고 있으며, 이에 근거하여 홍수예보 및 하천관리 업무에 효과적으로 활용하고 있다. 본 연구에서는 초음파 유량계가 설치된 여주지점의 2009년도 자동유량측정성과 중 동역학적 노이즈이라 판단되는 신호에 대하여 노이즈저감에 관한 방법론을 검토하고자 한다. 이를 위해 노이즈저감과 시간과 주파수 영역에서 유연한 분해능을 갖는 웨이블릿 변환을 적용하였으며 다양한 웨이블릿 변환함수 중 'db4'를 이용하였다. 여주지점의 자동유량측정성과에 대한 웨이블릿 변환함수 'db4'를 적용한 결과, 30분 이하의 단주기 성분(D1 등)은 동역학적 노이즈으로 판단되었으며, 최종파형분해단계의 근사성분은 원자료에 근사한 결과값을 얻을 수 있었다. 또한, 최종 분해된 자료는 충주조정지댐 방류량과의 상 하류 유출량 분석과 유출률 분석에서 물리적으로 해석이 가능한 결과 값을 얻을 수 있었다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.3
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• pp.40-48
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• 2003

Computer loads can be found in all of modem society. The switching mode power supplies used in personal computers are major sources of harmonic currents. Harmonic currents can cause lots of harmonic problems such as voltage waveform distortion, excessive neutral currents, errors in measurements, and disruption in computer performance. The purpose of this paper is to give an equivalent circuit modeling methodology for the harmonic currents generated by single-phase personal computer loads and to evaluate a commercially available series resonant filter for the harmonic currents compensation based on the IEEE 519-1992 and IEC1000-3-2 standards for limiting harmonic distortion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.23-32
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• 2020

The compression sensing technology, CAFB, was developed to obtain the raw signal of the target structure by compressing it into a signal of the intended frequency range. At this point, for compression sensing, the CAFB can be optimized for various reference signals depending on the desired frequency range of the target structure. In addition, optimized CAFB should be able to efficiently compress the effective structural answers of the target structure even in sudden/dangerous conditions such as earthquakes. In this paper, the targeted frequency range for efficient structural integrity monitoring of relatively flexible structures was set below 10Hz, and the optimization method of CAFB for this purpose and the seismic response performance of CAFB in seismic conditions were evaluated experimentally. To this end, in this paper, CAFB was first optimized using Kobe seismic waveform, and embedded it in its own wireless IDAQ system. In addition, seismic response tests were conducted on two span bridges using Kobe seismic waveform. Finally, using an IDAQ system with built-in CAFB, the seismic response of the two-span bridge was wirelessly obtained, and the compression signal obtained was cross-referenced with the raw signal. From the results of the experiment, the compression signal showed excellent response performance and data compression effects in relation to the raw signal, and CAFB was able to effectively compress and sensitize the effective structural response of the structure even in seismic situations. Finally, in this paper, the optimization method of CAFB was presented to suit the intended frequency range (less than 10Hz), and CAFB proved to be an economical and efficient data compression sensing technology for instrumentation-monitoring of seismic conditions.

• Journal of Biomedical Engineering Research
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• v.19 no.6
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• pp.595-602
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• 1998

Among the apex locators, the frequency dependent type is more accurate and convenient to use than others, But the accuracy of the apex locator is still influenced by the presence of various electrolytes used in root canal treatments. In this study, we have developed a frequency dependent electronic apex locator minimizing the influence of the electrolytes on the measurement of root canal lengths. It was also confirmed that two frequencies of 500Hz and 100kHz are optimal for the measuring impedance compare with commercial product used(400Hz and 8kHz)a and there were no differences in accuracy among the three different types of the waveforms; sinusoidal, triangular, and rectangular waves(p>0.05). Impedance ratio of the two different frequencies represents the position of the file in root canal, and the voltage difference of two signals represents the status of the fluid in the root canal. As a result of compensation using the voltage differences, the errors were decreased on the average from +0.54mm to +0.18mm in $H_2O_2$ solution (p<0.01), and from -0.33mm to -0.01mm in NaOCl solution(p<0.01). The accuracies based on ${\pm}$0.5mm, in $H_2O_2$ and NaOCl solutions were improved with the automatic compensation from 71.1% and 91.1% to 82.2% and 100% respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.2
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• pp.235-244
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• 2014

This paper describes the subarray channel configuration and calibration method for airborne AESA radar antenna. AESA radar demonstrator was designed and implemented for the digital beam-forming performance test of the 12 channel subarray structure. Magnitude and phase difference can be exist between the manufactured subarray channel. In this paper, calibration method for the subarray difference error was suggested. We measured digital monopulse slope in the subarray channel and verified the channel calibration effect. To verify the subarray channel operation, digital monopulse channel was compared with analog monopulse channel performance. AESA radar demonstrator was tested in the ground far field test range. Emulated single target was generated to test the detection and tracking performance of the demonstrator with the same waveform and search pattern. We verified that the detection and tracking performance of the 12 subarray digital monopulse channel was similar with the conventional analog monopulse channel. Also, ABF(Adaptive Beam-Forming) function for the sidelobe jammer was tested and effective operation was verified.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.17-33
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• 2007

Downhole seismic method is widely used for obtaining shear wave velocity profile of a site because it is simple and economical. Determining accurate travel time of shear wave is very important to obtain reliable result in downhole seismic method. In this paper, comparison study of various travel time determination methods was performed. Numerical study and model chamber test were performed for effective comparison study. Signal traces were acquired by performing downhole test at each numerical simulation and soil box test. Travel time data for each signal traces were determined by using six different methods and Vs profiles were evaluated. Comparing travel time data and Vs profiles with the reference value, the first arrival picking method proved to be ambiguous and unreliable. Other methods also did not always provide accurate results and the magnitude of error was dependent on the signal to noise ratio. Cross-correlation method proved to be the most adequate method for the field application and it was verified additionally with field data.

• Phonetics and Speech Sciences
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• v.15 no.4
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• pp.53-60
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• 2023

This study compared the absolute error of estimated fundamental frequency (AEF0) using voice - (VRP) and speech range profile (SRP) tasks across various etiological groups with voice disorders. Additionally, we explored the association between AEF0 and related voice parameters within each specific etiological group. The participants included 120 individuals, comprising 30 each from the functional (FUNC), organic (ORGAN), and eurological (NEUR) voice disorder groups, and a normal control group (NC). Each participant performed voice and SRP tasks, and the fundamental frequency of connected speech was measured using electroglottography (EGG). When comparing the AEF0 measures across the etiological groups, there were no differences in Grade and Severity among the patients. However, variations were observed in AEF0_VRP and AEF0_SUM. Specifically, AEF0_VRP was higher in the ORGAN group than in the FUNC and NC groups, whereas AEF0_SUM was higher in the ORGAN group than in the NC group. Furthermore, within FUNC and NEUR, AEF0 showed a positive correlation with Grade, while in ORGAN, it exhibited a positive correlation with the mean closed quotient (CQ). Attention should be paid to the application of AEF0 measures and related voice variables based on the etiological group. This study provides foundational information for the clinical application of AEF0 measures.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.12 no.1
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• pp.42-62
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• 2008

Objectives: It is well known that some parameters of the photoplethysmogram (PPG) acquired by time domain contour analysis can be used as markers of vascular aging. But the previous studies that have been performed for frequency domain analysis of the PPG to date have provided only restrictive and fragmentary information. The aim of the present investigation was to determine whether the harmonics extracted from the PPG using a fast Fourier transformation could be used as an index of vascular aging. Methods: The PPG was measured in 600 recruited subjects for 30 second durations, To grasp the gross age-related change of the PPG waveform, we grouped subjects according to gender and age and averaged the PPG signal of one pulse cycle. To calculate the conventional indices of vascular aging, we selected the 5-6 cycles of pulse that the baseline was relatively stable and then acquired the coordinates of the inflection points. For the frequency domain analysis we performed a power spectral analysis on the PPG signals for 30 seconds using a fast Fourier transformation and dissociated the harmonic components from the PPG signals. Results: A final number of 390 subjects (174 males and 216 females) were included in the statistical analysis. The normalized power of the harmonics decreased with age and on a logarithmic scale reduction of the normalized power in the third (r=-0.492, P<0.0001), fourth (r=-0.621, P<0.0001) and fifth harmonic (r=-0.487, P<0.0001) was prominent. From a multiple linear regression analysis, Stiffness index, reflection index and corrected up-stroke time influenced the normalized power of the harmonics on a logarithmic scale. Conclusions: The normalized harmonic power decreased with age in healthy subjects and may be less error prone due to the essential attributes of frequency domain analysis. Therefore, we expect that the normalized harmonic power density can be useful as a vascular aging marker.

• Geophysics and Geophysical Exploration
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• v.24 no.1
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• pp.6-19
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• 2021

Subsurface physical properties can be obtained and imaged by seismic exploration, and various algorithms have been developed for this purpose. In this regard, root mean square error (RMSE) has been widely used to quantitatively evaluate the accuracy of the developed algorithms. Although RMSE has the advantage of being numerically simple, it has limitations in assessing structural similarity. To supplement this, full-reference image quality assessment (FR-IQA) techniques, which reflect the human visual system, are being investigated. Therefore, we selected six FR-IQA techniques that could evaluate the obtained physical properties. In this paper, we used the full-waveform inversion, because the algorithm can provide the physical properties. The inversion results were applied to the six selected FR-IQA techniques using three benchmark models. Using salt models, it was confirmed that the inversion results were not satisfactory in some aspects, but the value of RMSE decreased. On the other hand, some FR-IQA techniques could definitely improve the evaluation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1155-1164
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• 2011

In this paper, we proposed the transmit beam measurement method of active phased array antenna, which is installed in Korea's first developed naval medium range radar, using near-field measurement facility. The pulse-mode high power characteristics of active phased array antenna's trasmit-beam make it difficult to measure with general near-field measurement facilities where low power continuous RF signals are used. Thus, in this paper, the measurement method of active phased array antenna's transmit beam in conjunction with the near-field measurement facility, which is suitable for the high-power transmit beam measurement, and PNA-X network analyzer(Agilent Technologies), which can support pulse-mode measurement, was proposed and measured by near-field measurement techniques. And the EIRP(Effective Isotropic Radiated Power), the transmit characteristic of active phased array antenna, was measured by the near field measurement techniques and compared to numerical estimation which was nearly equal with small difference of 0.1 dB.