• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.12
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• pp.19-23
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• 1991

A method for suppressing unwanted resonance modes by attaching an electromagnetic wave absorber onto a metal case was studied to prevent performance deterioration of electronic devices. The electromagnetic wave absorber fabricated for this study had an attenuation characteristics above 20dB in the frequency band from 450MHz, 1150MHz. A rectangular cavity resonator whose resonance frequencies of TE$_{101}$, TE$_{102}$ modes were 900MHz, 1250MHz, respectively, was made to measure attenuation for the electromagnetic wave absorber-metal assembly. The result showed that the resonance mode for high attenuation was sensitive to the location of electromagnetic wave absorber, and the attenuation characteristics above 20dB could be obtained when electromagnetic wave absorber was properly positioned.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.5
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• pp.438-445
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• 2007

A Helmholtz resonator as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified by linear acoustic analysis and atmospheric acoustic tests. To compare the results of acoustic attenuation effect in accordance with uni-resonator's geometry, quantitative analyses were made in the cases of various orifice diameters and lengths. Next, in the experiments to compare the results of acoustic attenuation effect by a difference in the number of resonators, damping capacity of harmful resonant frequency was improved by the increase of the number of resonators. On the other hand, attenuation efficiency of the frequency tended rather to lower due to over damping from the point of view of absorption coefficient. As the result, tuning the suitable geometry for the resonator to the resonant frequency is required for the control using the resonator. Also, the design of resonator's geometry and the choice of its number are important to put up the optimal efficiency in consideration of restriction of its volume.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.40-45
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• 2011

In this paper, to develop a broadband power line communication modem and network technologies, we analysis the characteristics of underground power line communication channel through actual tests. To measure the amount of attenuation by length and structure of broadband power line communication channel, we configure a measurement system of the channel with signal generator, spectrum analyzer and non-contacted coupler. For actual tests, we choose two of the longest lines among medium-voltage lines as a single line in the test lines and measure the characteristics of noise and signal attenuation level of the channel. The experimental results show that the channel has a impulse noise which can remarkably reduce communication capability. In the case of long lines, high-frequency attenuation appeared by length of the lines.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.4
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• pp.21-27
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• 2015

Induction bending is a method that allows the bending of any material that conducts electricity. This technology applies a bending force to a material that has been locally heated by an eddy current induced by a fluctuating electromagnetic field. Induction bending uses an inductor to locally heat steel through induction. This results in a narrow heat band in the shape to be bent. In general, the reduction of thickness attenuation of a large-diameter steel pipe is not allowed to exceed 12.5%. In this paper, in order to meet the standard of thickness attenuation reduction, a non-uniform heating temperature jump-bending process was investigated. As a result, the developed bending technique meets the requirements of thickness attenuation reduction for large-diameter steel pipes.

• Korean Journal of Agricultural and Forest Meteorology
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• v.2 no.3
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• pp.80-86
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• 2000

Eddy covariance method is widely used in measuring vertical fluxes of mass and energy between the atmosphere and the biosphere. In this method, scalar concentration is measured with either open-path or closed-path sensors. For the latter, fluctuations of scalar concentration are attenuated as the sample travels through a long tube, resulting in flux loss. To quantify this tube attenuation, water vapor concentrations measured with both closed-path and open-path sensors were analyzed. Our statistical analysis showed that the power spectral density obtained from the closed-path sensor was different from that from the open-path sensor in the frequency range of > 0.5 Hz. The loss of water vapor flux due to tube attenuation was < 5% during midday. At nighttime, however, the flux loss increased significantly because of the low wind speeds and the weak turbulence sources. Theoretical calculation for the tube attenuation showed a small bias in high frequency range probably because of the interaction of sticky water vapor with a tube wall.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.69
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• pp.65-73
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• 2001

The objective of this study is to evaluate the vibration attenuation effects of the different type of gloves and drilling mode while operating a light-weighted powered hand drill. For the experimental design, five different kinds of glove(barehanded cotton partly coated anti-vibration, and open-finger vibration glove) two types of push force level(100N and 200N) and two types of drilling mode(impact and non-impulsive) were considered. Six healthy male subjects were employed to drive screws into a vertically mounted marble plate with a powered hand drill in a randomly ordered experimental conditions. The findings of this study are summarized as follows; (1) It was found that the best combination of overall BMS transmissibility was using impact drilling mode with anti-vibration glove among evaluated experimental conditions (2) The wearing open finger vibration glove in mid-frequency level and anti-vibration glove with impact drill in high-frequency were the best in the result from mean corrected transmissibility equation of ISO 10819.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.280-285
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• 2000

It is very important to evaluate the surface or subsurface microstructure because of their influences on mechanical properties of materials. Surface SH-wave which is horizontally polarized shear wave traveling along near surface and subsurface layer is an attractive technique for material evaluation. The destructive method is widely used for the estimation of material degradation but it has a great difficulty in preparing specimens from in-service industrial facilities. In this study, nondestructive evaluation for degraded structural materials used at high temperature though surface SH-wave method is discussed. 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $650^{\circ}$ were evaluated though ultrasonic nondestructive evaluation techniques investigating the change of sound velocity, attenuation coefficient and amplitude spectra. In addition, it has verified experimentally the frequency-dependence of attenuation coefficient though wavelet analysis method.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.1
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• pp.1-7
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• 2002

The purpose of this work is to develop High-Frequency Active Filter and super-miniaturation technology(SMD Type) of Filter which are essential for the key R/F Microwave components in the Mobile telecommunication system. The cut-off frequency of high frequency active filter for multimedia is 2.5 MHz, the gain is 0.5dB at 100 kHz, the passband ripple is 1.2 dB max at 100 kHz~2.0 kHz, GDT is 60 nsec at 100 kHz-2.0 MHz, the attenuation is 40 dB min at 3.75 MHz.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.10
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• pp.67-75
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• 1998

This paper examined the geometrical variables of microstrip to control the characteristic impedance of MCM interconnect and also with respect to the practical requirements, evaluated the critical lengths for attenuation, propagation delay, and crosstalk at 500 MHz frequency compared to at 50 MHz frequency. With the illustration of each MCM-L and MCM-D interconnect having 50 characteristic impedance, it was revealed that the most important geometrical variables to control the characteristic impedance of microstrip are eventually dielectric thickness and line width. In particular, the dielectric thickness of MCM-D interconnect must be controlled with tolerance below 2 m. It is clear that the attenuation does not give rise to signal distortion in the range of up to 500MHz frequency for both MCM-L and MCM-D interconnects. However, the propagation delay is so significant that both MCM-L and MCM-D interconnects should be matched with load at the 500 MHz frequency. For the MCM-D interconnect, the crosstalk voltage would not be high to generate the wrong signal on the neighboring line at 500 MHz frequency, but the MCM-L interconnect could not be used due to severe crosstalk. Eventually, it is clear that the transmission line behavior must be studied for the design of MCM substrate at the 500 MHz frequency.

• Korean Journal of Applied Biomechanics
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• v.30 no.3
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• pp.197-204
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• 2020

Objective: The purpose of this study was to investigate the effect of increased running speed on the magnitude of impact shock attenuation in high frequency (9~20 Hz) at support phase on the treadmill running. Method: Twenty-four healthy male heel-toe runners participated in this study. Average age, height, mass, and preference running speed were 23.43±3.78 years, 176.44±3.38 cm, 71.05±9.04 kg, and 3.0±0.5 m/s, respectively. Three triaxial accelerometer (Noraxon, USA) were mounted to the tuberosity of tibia, PSIS (postero-superior iliac spine), and forehead to collect acceleration signals, respectively. Accelerations were collected for 20 strides at 1,000 Hz during treadmill (Bertec, USA) running at speed of 2.5, 3.0, 3.5, and 4.0 m/s. Power Spectrum Density (PSD) of three acceleration signals was calculated to use in transfer function describing the gain and attenuation of impact shock between the tibia and PSIS, and forehead. One-way ANOVA were performed to compare magnitude of shock attenuation between and within running speeds. The alpha level for all statistical tests was .05. Results: No significant differences resulted for magnitude of the vertical and resultant impact shock attenuation between the tibia and PSIS, and forehead between running speeds. However, significant differences within running speed were found in magnitude of the vertical shock attenuation between tibia and PSIS, tibia and forehead at speed of 2.5, 3.0 m/s, respectively. Conclusion: In conclusion, it might be conjectured that muscles covering the knee and ankle joints and shoe's heel pad need to strengthen to keep the lower extremities from injuries by impact shock at relatively fast running speed that faster than preferred running speed.