• 한국정보통신학회논문지
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• 제24권2호
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• pp.276-284
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• 2020

본 논문에서는 인지 무선 통신을 위한 새로운 합성곱 신경망 기반 스펙트럼 센싱 기법을 제안한다. 제안하는 기법은 주 사용자 신호에 대한 어떠한 사전 정보도 알지 못하는 상황에서 에너지 검출을 통해 주 사용자 신호 유무를 판단한다. 제안하는 기법은 센싱하고자 하는 전체 대역을 고려하여 수신신호를 고속으로 샘플링한다. 이후 신호의 FFT(fast Fourier transform)을 통해 주파수 스펙트럼으로 변환하고 연속적으로 이와 같은 스펙트럼을 쌓아서 2차원 신호를 만든다. 이렇게 만든 2차원 신호를 탐지하고자 하는 채널 대역폭 단위로 자르고 합성곱 신경망에 입력하여 채널이 사용 중인지 비어있는지 판단한다. 판단하고자 하는 분류의 종류가 두 가지이므로 이진 분류 합성곱 신경망을 사용한다. 제안하는 기법의 성능은 컴퓨터 모의실험과 실제 실내환경에서의 실험을 통해 검증하는데 이 결과에 따르면 제안하는 기법은 기존 문턱값 기반 기법보다 2 dB 이상 우수한 성능을 보인다.

• 전기학회논문지P
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• 제66권4호
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• pp.200-205
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• 2017

In this paper, we propose a technique to determine the normal and arc of an alternating current using a mixed filter composed of an average filter and a band-pass filter and a frequency analysis. The proposed method uses the moving average filter of the FIR filter structure for noise removal and the band-pass filter of the IIR filter structure for detecting only specific frequency components after normalizing the measured current signal based on the maximum value. After performing Fast Fourier Transform (FFT) using the band-pass filtered signal, the total energy is calculated using the magnitude component of the frequency, and the arc is detected using the magnitude of the calculated energy. In order to show the validity of the proposed method, we experimented with various data and found that arc and steady state can be easily discriminated by calculating spectral energy. Therefore, it is considered that the proposed method can be applied to arc diagnosis of low voltage electric wire.

• 한국음향학회지
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• 제16권5호
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• pp.105-111
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• 1997

수은이 다른 물이 층상구조를 이루고 있는 수중에서의 초음파 음장해석에 각 스펙트럼법을 도입하기 위하여, 그 도입에 따른 유효성과 오차의 정도를 가상의 경계를 고려한 등수은의 수층을 이용하여 분석하였다. 그 결고, 각 스펙트럼법은 단시간내에 비교적 정확한 음장산출이 가능하나 해석시 필요한 기준음장의 공간적 영역의 제한 및 푸리에변환시의 데이터 수의 제한으로 인하여 다소 오차을 발생시킴을 확인하였다. 그 오차를 감소시키기기 위한 한 방안으로 Lommel 근사법과 각 스펙트럼법을 복합하는 새로운 방법을 제안하였는데, 그 방법은 산출된 음장의 오차를 감소시키는데 유효하였다.

• 한국소음진동공학회논문집
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• 제20권9호
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• pp.863-875
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• 2010

The vibration of a cylindrical shell is generated due to elastic waves propagating on the shell. Those elastic waves include propagating waves such as flexural, longitudinal and shear waves. Those also include non-propagating decaying waves, i.e. evanescent waves. In order to separate contributions of each type of waves to the data for the vibration of the cylindrical shell, spatial signal processing techniques for wavenumber analysis are investigated in this paper. Those techniques include Fast Fourier transform(FFT) algorithm, Extended Prony method and Overdetermined Modified Extended Prony method(OMEP). Those techniques have been applied to identify the waves from simulated vibration signals with various signal-to-noise ratios. Futhermore, the experimental data for in-plane vibration of the cylindrical shell has been processed with those techniques to identify propagating waves(longitudinal, shear and flexural waves) and evanescent waves.

• 터널과지하공간
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• 제11권1호
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• pp.14-19
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• 2001

발파진동을 계측하여 예측방법의 타당성을 검토하였고, 환경규제 기준으로의 변환방식을 규명하였다. 진동레벨과 진동속도의 환산거리 설계 적용성은 진동속도가 더 좋았다. 따라서 설계나 시공은 진동속도로 관리하고 이를 법적 기준인 진동레벨로 변환할 필요성이 있었다. 기존의 변환식 중에서 충격진동 데이터로만 구성하여 변환식을 구하였고, 동시에 측정된 진동속도와 진동레벨의 상관식에 의한 변환식을 구하였으며, 퓨리에 변환을 하여 각 주파수 별로 감각보정하여 진동레벨을 구하였다. 세 가지 방법을 이용하여 변환한 결과 모두 오차가 있으므로 변환에 의한 피해 보상의 판정에는 무리가 있었으나, 그 중에서 발파시 동시에 측정된 수직방향 성분 PPV와 진동레벨의 변환식이 가장 실용적으로 판단되었다.

• 디지털산업정보학회논문지
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• 제5권4호
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• pp.11-17
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• 2009

Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode. More, I developed the experiment for raising up mercury electrode. In Voltammetry, information about an analyte is obtained by measuring the current as the potential is varied at oxidation-reduction reaction. A plot of current vs. potential in a polarography experiment shows the current oscillations correspoding to the drops of Hg falling from the capillary. The drops growth causes capacitive and faradic current. These changing current effects combined with experiments where the potential is continuously changed can result in noisy traces. The raising up type improved upon the method of dropping in hardware. In reduction of the noise, moving average smoothing method have been used. But the other procedure is introduced based on Fourier transformation. So FFT and IFFT engine was implemented and installed in my experiment. However, after experimentation, peak height as the measuring parameter gave a good linear relationship to concentration. The resolution of potential peaks of various kinds, using Zn and Cu as the example, was improved using the smoothing method.

• Structural Engineering and Mechanics
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• 제31권2호
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• pp.211-223
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• 2009

Transient response analysis can be conducted either in the time domain, or via the frequency domain. Sometimes a frequency domain method (FDM) has advantages over a time domain method. A practical issue in the FDM is to find out an appropriate extended period, which may be affected by several factors, such as the excitation duration, the system damping, the artificial damping, the period of interest, etc. In this report, the extended period of the FDM based on the Duhamel's integral is investigated. This Duhamel's integral based FDM does not involve the unit impulse response function (UIRF) beyond the period of interest. Due to this fact, the ever-lasting UIRF can be simply set as zero beyond the period of interest to shorten the extended period. As a result, the preferred extended period is the summation of the period of interest and the excitation duration. This conclusion is validated by numerical examples. If the extended period is too short, then the front portion of the period of interest is more prone to errors than the rear portion, but the free vibration segment is free of the wraparound error.

• Smart Structures and Systems
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• 제18권3호
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• pp.541-568
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• 2016

The goal of this study is to investigate the effect of non-synchronous sensing when using wireless sensors on structural identification and to attempt correcting such errors in order to obtain a better identification result. The sources causing non-synchronous sensing are discussed first and the magnitudes of such synchronization errors are estimated based on time stamps of data samples collected from Imote2 sensors; next the impact of synchronization errors on power spectral densities (PSDs) and correlation functions of output responses are derived analytically; finally a new method is proposed to correct such errors. In this correction method, the corrected PSDs of output responses are estimated using non-synchronous samples based on a modified FFT. The effect of synchronization errors in the measured output responses on structural identification and the application of this correction method are demonstrated using simulation examples. The simulation results show that even small synchronization errors in the output responses can distort the identified modal and stiffness parameters remarkably while the parameters identified using the proposed correction method can achieve high accuracy.

• Journal of Multimedia Information System
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• 제8권1호
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• pp.1-10
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• 2021

Heart Rate is a crucial physiological parameter that provides basic information about the state of the human body in the cardiovascular system, as well as in medical diagnostics and fitness assessments. At present day, it has been demonstrated that facial video-based photoplethysmographic signal captured using a low-cost RGB camera is possible to retrieve remote heart rate. Traditional heart rate measurement is mostly obtained by direct contact with the human body, therefore, it can result inconvenient for long-term measurement due to the discomfort that it causes to the subject. In this paper, we propose a non-contact-based remote heart rate measuring approach of the subject which depends on the color intensity variation of the subject's facial skin. The proposed method is applied in two regions of the subject's face, forehead and cheeks. For this, three different algorithms are used to measure the heart rate. i.e., Fast Fourier Transform (FFT), Independent Component Analysis (ICA) and Principal Component Analysis (PCA). The average accuracy for the three algorithms utilizing the proposed method was 89.25% in both regions. It is also noteworthy that the FastICA algorithm showed a higher average accuracy of more than 92% in both regions. The proposed method obtained 1.94% higher average accuracy than the traditional method based on average color value.

• 조명전기설비학회논문지
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• 제13권2호
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• pp.80-87
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• 1999

본 논문은 신경회로망을 이용하여 배전선로상의 고저항 사고검출기법을 제안하였다. 다양한 토양에서 실시한 고저항 사고 데이터를 통해 $\upsilon-i$ 특성곡선을 얻고, 이 특성곡선으로 EMTP를 이용하여 고저항 사고를 모의하였다. 배전선로 고저항 사고검출을 위해 훈련 모델은 강자갈을 사용하였고, 토양의 조건을 달리하여 신경회로망의 사고검출 성능을 평가하였다. 신경회로망의 입력으로 사고 전류를 주파수 분석한 후, 이를 한 주기 평균하여 얻어진 짝.홀수 고조파, 기본파, 실효치 지수을 이용하였다. 신겨회로망의 검출성능을 테스트한 결과 제안된 방법이 뛰어남을 확인하였다.