• 전기학회논문지
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• 제62권7호
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• pp.891-897
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• 2013

The power system frequency plays an important role in monitoring and controlling the power system. The frequency can be measured through discrete Fourier transform (DFT) coefficients of its positive fundamental frequency. The accuracy of the frequency estimate is severely affected by noise in the power system signal and the leakage effect of the negative fundamental frequency in DFT. This paper proposes a DFT-based frequency estimation algorithm to cope with the noise as well as the leakage effect. In this algorithm, two suitable digital filters are introduced to reduce efficiently frequency estimate error due to the noise. These filters are designed to use a digital bandpass filter and a second-degree integrator. The effectiveness of the proposed algorithm in reduction of frequency estimate error is verified through simulations on noise, harmonics and frequency deviation.

• 한국항행학회논문지
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• 제3권2호
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• pp.120-131
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• 1999

마그네트론을 이용하여 송신 펄스를 발생하는 레이다에서 위상을 측정하기 위해서는 송신주파수의 변화에 대해서도 안정된 중간주파수를 발생할 수 있도록 STALO(Stable Local Oscillator)의 주파수를 조정하여야 한다. 레이다 수신기의 AFC(Automatic Frequency control) 회로는 마그네트론에서 발생하는 송신주파수와 STALO의 국부발진주파수를 비교하여 일정한 중간주파수가 발생하도록 STALO 주파수를 제어한다. 본 논문에서는 안정된 중간주파수를 발생하기 위한 AFC 회로를 설계, 제작하였으며, 주파수 변화를 검출하여 비교하는 아날로그 부분과 STALO에 주파수 제어신호를 공급하는 디지털 부분을 개발하였다.

• 지능정보연구
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• 제22권2호
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• pp.115-125
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• 2016

현재 주가가 최근 움직임 범위 내에서 어떤 위치에 있는지를 나타내는 블린저밴드 (Bollinger Band)는 단순이동평균 (Simple Moving Average)을 중심으로 단순표준편차 (Simple Standard Deviation)를 가감하여 만들어진다. 본 논문에서는 먼저 단순이동평균과 지수이동평균 (Exponential Moving Average)의 특성을 연산자 (Operator)의 관점에서 살펴보고, 각 연산자들의 임펄스응답 (Impulse Response) 1차 모멘텀의 중심값을 동일하게 하는 조건으로부터 단순이동평균 구간크기 N과 지수이동평균의 가중치 ${\rho}$ 사이의 관계를 구한다. 다음으로 이산시간 프리어변환 (Discrete Time Fourier Transform)을 통해 1차 모멘텀의 중심값이 동일하다는 조건하에서의 각 연산자의 주파수 응답 (Frequency Response)의 특성을 비교한다. 단순이동평균연산자는 지수이동평균연산자에 비해 고주파성분을 더 많이 포함시키므로 주가의 움직임에 과도하게 반응하게 된다는 사실에 기초하여, 지수이동평균을 중심으로 하는 새로운 ESD밴드 (Exponential Standard Deviation Band, 지수표준편차밴드)를 제안하고 자기회귀 (Auto Recursive) 형태의 계산공식을 유도하고 동일조건하에서 블린저밴드와 ESD밴드를 실제의 예를 통해 비교한다. 제안한 ESD밴드는 주가 움직임 범위를 보다 부드럽게 표현하는 특징이 있으며, 날짜 변경 시 갭이 발생할 경우에도 이러한 장점을 살리기 위해 갭보정된 차트에 대한 ESD밴드와 블린저밴드의 비교도 함께 살펴본다. 기존의 블린저밴드를 이용하여 개발된 거래법들은 ESD밴드에 그대로 적용가능하다.

• 한국안전학회지
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• 제14권3호
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• pp.101-109
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• 1999

This study attempts to analyse the solid mixing in the feeder and the packing effect for pressure fluctuations in the fluidized bed. To study the mixing characteristics of solid in vibrating feeder for the stable operations of fluidized combustion, the system consisted of two groups of particles such that fine particles were located on the top of the coarse particles before vibratory mixing had started. The effects of packing materials on the pressure fluctuations in a fluidized bed were analysed by using a statistical method to interpret the behavior of fluidized bed. The experiments were carried out in a fluidized bed of 6.7cm-ID, and the experimental variables were particle sizes, of 115 to 1,015$\mu\textrm{m}$ in diameter and the multi-sized particles haying Rosin-Rammler and Gaussian distributions. The settled bed heights of particles to diameter ratios (L/D) were ranged from 0.5 to 2.0. And fluidizing of particles was carried out by air. The packing materials used were screen packing, and the properties of the pressure fluctuations in the fluidized bed were measured by a differential pressure transducer. The properties of the pressure fluctuations calculated were the mean, the standard deviation, and the major frequency of the power spectral density functions. From the characteristics of fluidizing, it was found that the standard deviation of pressure fluctuations could be effectively used to explain the fluidized phenomena, and the packing materials affected severely the properties of the pressure fluctuations. As a result, from the interpretation by spectral analysis, the effects of measuring radius of pressure fluctuations on standard deviation were constant in the case of the fluidized bed with and without packing materials. However, the effects of measuring the height of pressure fluctuations on standard deviations were linear increasing for the fluidized bed with packing materials, but were constant for the fluidized bed without packing materials at 4.5cm above the gas distributor. The major frequency of pressure fluctuations was found to be nearly independent of fluidized system. Also, the major frequency of pressure fluctuations decreased with increasing packing size, and it had maximum value at 10% of the packing amount.

• International Journal of Control, Automation, and Systems
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• 제6권6호
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• pp.818-827
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• 2008

In this paper, we propose a new noise estimation and reduction algorithm for stationary and nonstationary noisy environments. This approach uses an algorithm that classifies the speech and noise signal contributions in time-frequency bins. It relies on the ratio of the normalized standard deviation of the noisy power spectrum in time-frequency bins to its average. If the ratio is greater than an adaptive estimator, speech is considered to be present. The propose method uses an auto control parameter for an adaptive estimator to work well in highly nonstationary noisy environments. The auto control parameter is controlled by a linear function using a posteriori signal to noise ratio(SNR) according to the increase or the decrease of the noise level. The estimated clean speech power spectrum is obtained by a modified gain function and the updated noisy power spectrum of the time-frequency bin. This new algorithm has the advantages of much more simplicity and light computational load for estimating the stationary and nonstationary noise environments. The proposed algorithm is superior to conventional methods. To evaluate the algorithm's performance, we test it using the NOIZEUS database, and use the segment signal-to-noise ratio(SNR) and ITU-T P.835 as evaluation criteria.

• Korea-Australia Rheology Journal
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• 제19권3호
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• pp.141-146
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• 2007

We examine the wall contact of a $3\;{\mu}m$ tethered DNA chain's free end under shear with a focus on developing schemes for double-tethering in the application of making scaffolds for molecular wires. At this scale our results are found to be highly dependent on small length scale rigidity. Chain-end-wall contact frequency, mean fractional extension deficit upon contact, and standard deviation in extension upon contact are examined for scaling with dimensionless flow strength, Wi. Predictions made using a one dimensional approximation to the Smoluchowski equation for a dumbbell and three dimensional dumbbell simulations produce extension deficit, standard deviation, and frequency scaling exponents of -1/3, -1/3, and 2/3, respectively whereas more fine-grained Kratky-Porod (KP) simulations produce scaling exponents of -0.48, -0.42, and 0.76. The contact frequency scaling of 2/3 is derived from the known results regarding cyclic dynamics Analytical scaling predictions are in agreement with those previously proposed for ${\lambda}-DNA$. [Ladoux and Doyle, 2000, Doyle et al., 2000]. Our results suggest that the differences between the dumbbell and the KP model are associated with the addition of chain discretization and the correct bending potential in the latter. These scaling results will aide future exploration in double tethering of DNA to a surface.

• 한국운동역학회지
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• 제17권1호
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• pp.129-134
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• 2007

The purpose of this study was to determine the variability of components of the vertical ground reaction force signal to seek the suitable number of attempt datum to be analyzed during running at 2m/s and 4m/s. For this study, six subjects (height mean:$174.5{\pm}4.4cm$, weight $671.5{\pm}116.4N.$, age:$25.0{\pm}yrs.$) were selected and asked to run at least 3 times each run condition randomly. FFT(fast Fourier transform) was used to analyze the frequency domain analysis of the vertical ground reaction forces signal and an accumulated PSD (power spectrum density) was calculated to reconstruct the certain signal. To examine the deviation of the vertical ground reaction between signals collected from an different number of attempt, variability of frequency, magnitude of passive peak, time up to the passive peak and maximum load rate were determined in a coefficient of variance. The variability analysis revealed that when analyze the vertical reaction force components at 2m/s speed running, which belongs to slow pace relatively, it would be good to calculate these components from signal of one attempt, but 4m/s speed running needs data collected from two attempts to decrease the deviation of signal between attempts. In summary, when analyzing the frequency and passive peak of the vertical reaction force signal during the fast run, it should be considered the number of attempt.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권2호
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• pp.202-207
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• 2015

A CMOS relaxation oscillator, with high robustness over process, voltage and temperature (PVT) variations, is designed in $0.18{\mu}m$ CMOS. The proposed oscillator, consisting of full-differential charge-discharge timing circuit and switched-capacitor based voltage-to-current conversion, could be expanded to a simple open-loop frequency synthesizer (FS) with output frequency digitally tuned. Experimental results show that the proposed oscillator conducts subcarrier generation for frequency-modulated ultra-wideband (FM-UWB) transmitters with triangular amplitude distortion less than 1%, and achieves frequency deviation less than 8% under PVT and phase noise of -112 dBc/Hz at 1 MHz offset frequency. Under oscillation frequency of 10.5 MHz, the presented design has the relative FS error less than 2% for subcarrier generation and the power dissipation of 0.6 mW from a 1.8 V supply.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.449-452
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• 2014

We present a multi-tap microwave photonic filter with high selectivity through applying time-to-frequency mapping and optical frequency comb shaping techniques. When arranged in the time-to-frequency mapping stage, by a Fourier transform, the deviation of the optical taps to the target profile is significantly reduced while maintaining the apodization profile, resulting in high sidelobe suppression in the filters. By applying a simple time-to-frequency mapping stage to the conventional optical frequency combs, we demonstrate a substantially enhanced (>10dB) sidelobe suppression, resulting in filter lineshapes exhibiting a significantly high (>40dB) main lobe to sidelobe suppression ratio. These results highlight the potential of the technique for implementation in various passband filters with high sidelobe suppression.

• 한국전자파학회논문지
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• 제27권3호
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• pp.299-306
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• 2016

본 논문에서는 공진기와 인체와의 거리에 따른 근접 전자기장 변화에 의한 공진기 임피던스의 변화를 토대로 사람의 호흡 및 심박신호를 검출할 수 있는 센서를 제안한다. 제안된 생체신호 측정센서는 패치형 공진기가 결합된 발진기, 발진주파수의 2채배 주파수만 통과시키기 위한 다이플렉서, 증폭기, SAW 필터 및 RF 검출기로 구성되어 있다. 호흡과 심박신호와 같은 인체의 주기적인 움직임은 근접 전자기장 영역 안에서 공진기의 임피던스 변화를 야기하며, 발진기의 주파수를 변화시킨다. 감도를 향상시키기 위해 발진주파수의 2채배 주파수 천이를 SAW 필터의 저지대역에 위치시킴으로써, 제안된 센서의 검출 거리를 2배로 확장시킬 수 있다. 제안된 센서의 측정결과, 최대 40 mm까지 호흡 및 심박신호가 안정적으로 측정되는 것을 확인하였다.