• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.1109-1115
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• 2008

In the ubiquitous health monitoring environments, it is quite important not only to evaluate the physiological health condition but also mental stress condition. In order to achieve this goal, a heart activity monitoring system utilizing a wearable bipolar electrode is devised and the heart rate variability(HRV) is extracted and interpreted in both frequency and time feature domains. Consequently, to evaluate the emotional stress condition of the subjects, a stress-induced experimental protocol was applied to healthy subjects and the time and frequency features of heart activity were analyzed in terms of the ratio of low frequency components v.s., high frequency components and the relevant the moving average distributions compromising the successive RR peaks intervals in the ambulatory ECG measurement system.

• Wind and Structures
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• v.11 no.2
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• pp.137-152
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• 2008

This paper discusses engineering aspects of the rear-flank downdraft that was recorded near Lubbock, Texas on 4 June 2002, and produced a gust wind speed nearly equal to the design value (50-year return period) for the region. The general characteristics of the storm, and the decomposition of the time histories into deterministic 'running mean' and random turbulence components are discussed. The fluctuating wind speeds generated by the event can be represented as a dominant low-frequency 'running mean' with superimposed random turbulence of higher frequencies. Spectral and correlation characteristics of the residual turbulence are found to be similar to those of high-frequency turbulence in boundary-layer winds. However, the low-frequency components in the running-mean wind speeds are spatially homogeneous, in contrast to the low-frequency turbulence found in synoptic boundary-layer winds. With respect to transmission line design, this results in significantly higher 'span reduction factors'.

• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.67-75
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• 2016

To investigate spatial and temporal variations of low-frequency (${\leq}5Hz$) ambient seismic noise, we analyzed the noise data recorded for one whole year of 2014 at surface accelerometer stations in South Korea. After decomposed into low-frequency (LF; < 1 Hz) and high-frequency (HF; ${\geq}1Hz$) components, the root-mean-squared (RMS) amplitudes and power spectral densities (PSD) of the noise data were computed. The RMS amplitudes were larger on islands and near-shore stations, but also large RMS amplitudes were observed at inland stations in large cities only for HF components. The RMS amplitudes of HF components were larger in the daytime than at nighttime and during weekdays than on Sunday and holidays. This indicates the HF components are closely related to human activities. On the contrary, daily and weekly variations were not clear in the LF components while they showed seasonal variations with its maximum during the winter and a good correlation with significant wave height. Therefore, we interpret the mechanism of LF components is closely related to natural phenomena such as sea. The amplitude of LF components decreased as an exponential function of the distance to the center of typhoons. The exponential index of -0.76 suggested that ambient seismic noise included both surface and body waves. Peak frequencies of the PSD curves were near 0.34 Hz indicating the double frequency. No temporal variation in the peak frequency was clearly noticed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.1
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• pp.47-51
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• 2000

To make a practical application of a micro-strain sensors with ultrahigh sensitivity, a strain on electrical properties of micro-patterned amorphous (Fe\ulcornerco\ulcorner)\ulcornerSi\ulcornerB\ulcorner films had influenced on the impedance over frequency range from 1 MHz to 1 GHz. Reflecting excellent magnetomachanical couping properties of films, high frequency impedance was subject to change sensitively by a strain : a change in impe-dance of 39% was observed at 200 MHz applied a strain of 224$\times$10\ulcorner. To determine a optimum shape of micro-patterned films, film impedance was analyzed by virtue of its constitutive components of resis-tance and reactance. Result was shown that reduction of the resistance term(hence increase of resultant reactance term) of impedance is more effective for enhancing the strain sensitivity of films at relatively low frequency range.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1292-1294
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• 1996

The general output circuit for PWM output is pushpull using a complimentary MOSFET. The gate driver coupled directly at gate can switch easy upto a high frequency. However, a high reverse recovery current and parastic components make a oscillation output. This paper analyses this phenomenon and proposes a novel output circuit preventing the oscillation.

• International Journal of Automotive Technology
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• v.8 no.1
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• pp.59-66
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• 2007

High frequency excitation terms in a cam profile can excite vibration of a cam follower system. In this paper, modified smoothing spline curves are used to reduce the high frequency terms. The essential difference between the proposed method and other existing approaches is its ability to make the principal cam motions smooth while still exactly satisfying boundary conditions of follower displacement, velocity and acceleration. The boundary values usually depend on the ramp properties of a cam. Our method, thus, allows designers to smooth the existing cam motion without any damages on its ramp areas. Because the ramp height, velocity and acceleration are maintained exactly, more radical smoothing is possible. An example shows that the proposed method can be a powerful tool of cam profile smoothing, which removes high frequency components in the cam profile excitations without any changes in ramp properties.

• Journal of Information Display
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• v.12 no.2
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• pp.109-113
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• 2011

This paper summarizes the recent fabrication and characterizations of flexible high-speed radio frequency (RF) transistors, PIN-diode single-pole single-throw switches, as well as flexible inductors and capacitors, based on single-crystalline Si nanomembranes transferred on polyethylene terephthalate substrates. Flexible thin-film transistors (TFTs) on plastic substrates have reached RF operation speed with a record cut-off/maximum oscillation frequency ($f_T/f_{max}$) values of 3.8/12 GHz. PIN diode switches exhibit excellent ON/OFF behaviors at high RF frequencies. Flexible inductors and capacitors compatible with high-speed TFT fabrication show resonance frequencies ($f_{res}$) up to 9.1 and 13.5 GHz, respectively. Robust mechanical characteristics were also demonstrated with these high-frequency passives components.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.755-758
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• 2001

In this paper. Ive propose a postprocessing technique based on the theory of projection on convex sets(POCS) to reduce the blocking artifacts in HDTV decoded images. In BDCT of HDTV. the image is divided into a grid of non-overlapped 8 ${\times}$ 8 blocks. and then each block is coded separately. A block which is located one pixel apart from the grid of BDCT will include the boundary of the original 8 ${\times}$ 8 block. If the blocking artifact is Introduced alone the block boundary. this block will have different frequency characteristic from that of the original block. Thus, a comparison of frequency characteristics of these two overlapping blocks can detect the undesired high-frequency components mainly caused by the blocking artifact. By eliminating these undesired high-frequency components adaptively, robust smoothing projection operator can be obtained. Simulation results with real image sequences indicate that the proposed method performs better than conventional algorithms.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.10
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• pp.495-501
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• 2002

A difference based current transformer (CT) saturation detection algorithm uses the third difference of a secondary current to detect the instants of the beginning/end of saturation. The third difference of a secondary current contains high frequency components when a CT is saturated. Thus, an effect of an anti-aliasing lowpass filter implemented in digital protection relays on the detection algorithm should be studied. This paper describes performance analysis of a lowpass filter on the CT saturation detection algorithm. The cutoff frequency of the lowpass filter is normally set to be half of a sampling frequency. In this Paper, two sampling frequencies of 3,840 (Hz) corresponding to 64 sample/cycle (s/c) and 1,920 (Hz) corresponding to 32 (s/c) are studied; the cutoff frequencies of the lowpass filters are set to be 1,920 (Hz), 960 (Hz) and 960(Hz), 480(Hz), respectively. And the proposed algorithm is verified by experiment. A 2nd order Butterworth filter is designed as a lowpass filter. The test results and experiment results clearly indicate that the saturation detection algorithm successfully detects the instants of the beginning/end of saturation even though a secondary current is filtered by the designed lowpass filters.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.2
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• pp.90-95
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• 2001

Electric arc furnaces (EAFs) has a process to cause the degradation of the electric power quality such as voltage flicker. In order to adequately understand and analyze the effects on the power system from these loads, obtaining an accurate representation of the characteristics of the loads is crucial. In this paper, a mixed chaotic EAF model to represent the low frequency and high frequency variations of the arc current respectively has been proposed. The Lorenz system may contribute to the low frequency components of arc current and the logistic equation may contribute to the high frequency components, and the proposed mixed model will be a combination of both Lorenz and logistic model. The concept of chaotic parameters, such as chaotic resistance, inductance of admittance has been also proposed for the characterization of arc furnace operation and the highly nonlinear physical processes. The power quality indices are calculated from the simulated waveforms and compared with the actual power quality indices statistics in order to illustrate the model's capabilities.