• Journal of Magnetics
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• v.19 no.2
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• pp.185-191
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• 2014

In this study we evaluated that flow rate changes affect the (time of flight) TOF image and contrast-enhanced (CE) in a three-dimensional TOF angiography. We used a 3.0T MR System, a nonpulsatile flow rate model. Saline was used as a fluid injected at a flow rate of 11.4 cm/sec by auto injector. The fluid signal strength, phantom body signal strength and background signal strength were measured at 1, 5, 10, 15, 20 and 25-th cross-section in the experienced images and then they were used to determine signal-to-noise ratio and contrast-to-noise ratio. The inlet, middle and outlet length were measured using coronal images obtained through the maximum intensity projection method. As a result, the length of inner cavity was 2.66 mm with no difference among the inlet, middle and outlet length. We also could know that the magnification rate is 49-55.6% in inlet part, 49-59% in middle part and 49-59% in outlet part, and so the image is generally larger than in the actual measurement. Signal-to-noise ratio and contrast-to-noise ratio were negatively correlated with the fluid velocity and so we could see that signal-to-noise ratio and contrast-to-noise ratio are reduced by faster fluid velocity. Signal-to-noise ratio was 42.2-52.5 in 5-25th section and contrast-to-noise ratio was from 34.0-46.1 also not different, but there was a difference in the 1st section. The smallest 3D TOF MRA measure was $2.51{\pm}0.12mm$ with a flow velocity of 40 cm/s. Consequently, 3D TOF MRA tests show that the faster fluid velocity decreases the signal-to-noise ratio and contrast-to-noise ratio, and basically it can be determined that 3D TOF MRA and 3D CE MRA are displayed larger than in the actual measurement.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.41-48
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• 2000

We have installed the borehole seismic recording system at Hyodongri in eastern part of Kyungsan Basin, which has the advantages of reduction in noise by human activities and distorting effects of near-surface rocks. Here we describe briefly the borehole seismic station and recording system. And we analyse the characteistics of back ground the station obtained from borehole sensors. The back ground noise level in time domain is about 50~100$\mu$cm/sec. The average curve of noise spectrum is lower than NHNM(New High Noise Model)of GSN(Global Seismic Network)operated by USGS. The results could be useful prior information for study on earthquake records observed at Hydongri station.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.93-101
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• 2014

Underwater radiated noise is the key in acoustic stealth performance of modern naval ships. The underwater radiated noise predicted by the hull vibration with radiation efficiency cannot always give the information of radiation pattern which is essential to analyze of detection probability by enemy and to improve the operational performance of the naval ship. The radiation pattern of underwater radiated noise is able to be obtained with radiation efficiency and radiation directional coefficient. In this paper, a new method to extract the radiation efficiency and radiation directional coefficient is suggested and proved with the simulation and experiment by using cylindrical shell of 70 cm diameter in air.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.4
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• pp.327-334
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• 2014

This paper presents a method of fault detection and fault localization from acoustic noise measurements. In order to detect the presence of noise sources wavelet transform is applied to acoustic signal. In addition, a cross correlation based method is proposed to calculate the exact location of the noise allowing the user to quickly diagnose and resolve the source of the noise. The fault detection system is implemented using two microphones and a computer system. Experimental results show that the system can detect faults due to artifacts accidentally inserted during the manufacturing process and estimate the location of the fault with approximately 1 cm precision.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.98-101
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%${\sim}$30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with USN. which are connected to the spectrum analyzer respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.738-743
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• 2013

Underwater radiated noise is the key in acoustic stealth performance of modern naval ships. The underwater radiated noise predicted by the hull vibration with radiation efficiency cannot give the information of radiation pattern which is essential to the analysis of detection possibility by enemy and to improve the operational performance of the naval ship. The radiation pattern of underwater radiated noise is able to be obtained with radiation efficiency and radiation direction coefficient. In this paper, a new method to extraction the radiation efficiency and radiation direction coefficient is suggested and proved with the simulation and experiment by using cylindrical shell of 70cm diameter in air.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.470-473
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• 2004

This paper presents conducted emission noise measurement from electronic equipment in frequency range of 1 MHz up to 30 MHz by small loop antenna. Small loop antenna measurement method can measure common-mode (CM) and differential-mode (DM) component of the noise on a pair of power line at the same time. The CM and DM can be measured separately. The theory of this measurement method is introduced and analyzed. The measured results were compared with the conventional measurement by Line Impedance Stabilization Network (LISN) and result a good trend between those methods.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.918-923
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• 2005

The vibration level (dB(V)) and vibration velocity (cm/sec) on the ground and buildings due to the differences of the measuring sites from the blasting source was investigated. To compare with vibration level and vibration velocity theirs magnitude was not surely directly proportional and vibration velocity 0.1 cm/sec was $45\~50$ dB(V). The difference between the measured vibration level and the calculated vibration level by Ejima's equation using vibration velocity PVS(peak vector sum) showed $21.0\~30.9$ dB(V) on the ground, $15.3\~23.6$ dB(V) on the apartment, respectively. And the correlation of vibration velocity and nitration level at the measuring sites of lower altitude showed higher than that of higher altitude.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.342-345
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• 2005

To detect external acoustic signal, fiber optic sensor array using Fabry-Perot interferometer which had benefit of minimize and light-weight was used. The sensor head has 1cm in length, total length of fiber is 9.5cm, and the sensor supported at both ends, simply. External sound applied in lateral direction and detected two signals were compared each other. It was confirmed that the Fabry-Perot interferometric sensor array detected acoustic signal, effectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.234-237
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• 2002

To detect external vibration signals on the latticed fence structure, distributed fiber optic sensor using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 170cm in width and 180cm in height, the optical fiber, 50m in length, distributed and fixed on the latticed structure. It was verified the sensitivity of the Sagnac interferometer using the PZT phase modulator. Fiber optic external vibration signal spplied to the latticed fence structure from 100Hz to several kHz. The interferometeric fiber optic sensor detected the excited vibration signal very effectively without any signal processing. The detected optical signals were compared and analyzed to the detected acclerometer signals.