• 대한의용생체공학회:의공학회지
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• 제11권2호
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• pp.227-232
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• 1990

As a part of the study on ultrasonic tissue characterization, conventional ultrasonic imaging system is interfaced to the personal computer to acquire raw ultrasonic signal. One approach for tissue charaterization is performed using the attenuation map to the conventional images and the resulting attenuation map images are compared and inspected inside the region of interest from the viewpoint of pattern analysis. Currently, these methods are applied and modified to effectively find out the differences between the normal control and the patients with liver cirrhosis.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.65.4-65
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• 2001

In case of data transmission using the upper 10GHz frequency, rain results in attenuation of radio waves. And the most serious atmospheric effect in a satellite link is the rainfall. The attenuation of rainfall very seriously affects the quality of transmission line. Because the rain increases thermal noise and interference, and decreases the amplitude of the signal. KOWACO manages the VSAT system instead of VHF network for communication of rain and water-level data from 1998. The purpose of this system is to monitor the change of water-level and rain data during a flood duration. VHF system acquires the data by a call per a hour. But the satellite network obtains the data whenever event data occur. Thus the satellite network is more powerful than the VHF system. In study ...

• Structural Monitoring and Maintenance
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• 제9권4호
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• pp.373-388
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• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• Journal of information and communication convergence engineering
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• 제3권3호
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• pp.146-151
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• 2005

This paper represents an attempt to bring together and analyses the measurement data measured by the Satellite Signal Monitoring Center in Korea and the Korea Meteorological Administration/Korea Meteorological Research Institute in close cooperation with this study team. This paper presents the signal characteristic of GEO satellite operating in frequency range 1 to 20GHz associated with Asian Sand Dust (the so-called Yellow Sand Dust). The downlink signal power (dBm) for L-, S-, C-, Ku-, and Ka-band frequencies from GEO satellites were measured in a clear weather and in Asian Sand Dust weather by the Satellite Signal Monitoring Center. The measured signal power(dBm) were compared to the total number concentration and size distribution of Sand Dust that were measured by the Korea Meteorological Administration/Korea Meteorological Research Institute and the possible correlation between these sets data were analyzed. The results demonstrate that the downlink signal level (dBm) of GEO satellite is attenuated by Asian Sand Dust. Hitherto, merger information has been reported as to the influence of sand dust on satellite communications operating in regions affected by sand dust.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1599-1601
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• 1999

The characteristics of ultrasonic signal in insulation oil were investigated by optical fiber sensor(OFS) utilizing Mach-Zehnder interferometer. For checking the response properties of OFS ultrasonic signal was generated by function generator in various kinds of insulation oil. The attenuation of ultrasonic signal linearly increased with the increase of viscosity of insulation oil in log scale. Discharging signal was produced by neele-sphere electrode system. Intensity of discharging signal was plotted in terms of cumulative $y^2$ and the intensity of discharging signal in new oil was little bigger than that in serviced one.

• 한국전자통신학회논문지
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• 제7권1호
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• pp.125-134
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• 2012

본 연구는 대기중에 포함된 미세먼지(PM10: 지름 $10{\mu}m$ 이하크기의 미세먼지)가 위성신호전송주파수대역에 미치는 영향을 해석하기 위한 것으로, 미세먼지 농도별 위성신호감쇠 정도를 해석을 위하여 $50{\mu}g/m^3$이하, $100{\mu}g/m^3$이하, $200{\mu}g/m^3$, $400{\mu}g/m^3$이하, $800{\mu}g/m^3$이하, $1,600{\mu}g/m^3$이하, $3,200{\mu}g/m^3$이하로 총 7단계로 분류하여 해당 농도가 위성신호에 미치는 영향을 정량화 하는 연구이다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(II)
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• pp.1247-1251
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• 1987

Cepstral analysis was performed on the ultrasonic echo signal from the tissue to achieve improvement on the estmation of the attenuation coefficient. In this paper, the feasibility of the acquiring the structural information of the tissue was also included by same method with band pass lifter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 D
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• pp.2597-2599
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• 2001

This paper has developed the power line interphone system with the amplitude modulation technique. We described the Amplitude modulation and demodulation circuit and the line coupler for the implementation of the power line interphone. and suggested the experimental result for the signal attenuation, demodulated signal, spectrum.

• 한국통신학회논문지
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• 제14권5호
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• pp.531-541
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• 1989

무선 수신기에 동일 주파수의 방해 신호를 제거하기 위하여, 적응 배열 안테나 프로세서를 구현하고 30-75MHz의 VHF 대역에서 방해 신호억압 효과 실험을 하였다. CW, AM 및 FM의 전파 형식으로 구분하여 방해 신호에 대한 억압 효과는 35dB를 얻었다. 시스템 구성은 1/4 파장의 수직 안테나 2개를 사용하였고, 최근의 초고주파 신호 처리용 소자를 이용하여 광대역 억압특성을 갖는 안테나 프로세서를 실현하였다.

• 한국정밀공학회지
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• 제21권9호
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• pp.63-68
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• 2004

The high pressure vessels that are constructed by welding process have many welding lines and most of the leakage defects are occurred on these welding lines. The acoustic emission(AE) technique has adopted to detect the defect location and leakage on welding parts, but the AE signal in leakage are incomplete due to the attenuation, reiteration, instability and limit of defect size. To overcome these troubles, the experiments in this study are conducted to measure the indirect media-propagated AE signal perpendicular to the leakage hole. The AE signals that are acquired from the direct and indirect media are analyzed, and the reliability of the indirect media-propagated AE signal are examined experimentally. By AE signal investigation, this method can be adopted to detect efficiently the leakage in welding parts.