• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.10
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• pp.1444-1450
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• 2013

Esophageal stethoscope is used for monitoring the heart sounds and breath sounds of patients during surgery under a general anesthesia. Recently, an electronic esophageal stethoscope (EES)[1] has been developed for the purpose of real-time monitoring these information visually. This system uses only a microphone as the sound sensor. A drawback of the EES system is that it may be difficult to distinguish the first sound ($S_1$) and the second sound ($S_2$) of heart, because their periods are irregular depending on patients. In this paper, we propose an improved EES system in which the infrasound is measured by adding a pressure sensor as well as a sound sensor. We investigate some correlations between the infrasound and characteristics of the heart sound. The proposed system has been tested on 15 patients. The results show that the new system is capable of detecting the first sound more reliably and easily determining the heart rate and breathing period.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.68-73
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• 2005

In succession of the previous works, seismo-acoustic analysis was conducted to collect ground truth events and to discriminate surface explosions from natural earthquakes in the Korean Peninsula for 2004. In this period, total 510 seismo-acoustic events corresponding to 10.8 percent of total seismic events occurred in and near the Korean Peninsula were analyzed and discriminated as artificial surface explosions. Events distribution of the seismo-acoustic events in 2004 is similar to the previous results of 1999-2003. And newly determined seismo-acoustic events were added to the surface explosions database. To extend infrasound detection capability, Korea Institute of Geoscience and Mineral Resources (KIGAM) and Southern Methodist University (SMU) installed new seismo-acoustic array (BRDAR) in Baekryoung Island last November, 2004. The array configuration and design is nearly same to previous seismo-acoustic arrays CHNAR, KSGAR, a triangular 1 km aperture. BRDAR consists of 5 short period vertical seismometers (GS-13) in seismic vaults and 13 microbarometers (Chaparral Model 2). Preliminary analysis using data collected from BRDAR shows an extension of infrasound detection capability to western part of the Korean Peninsula. Also, multiple observations of infrasound at BRDAR and other arrays gave an opportunity to localize sound source regions.

• Journal of the Korean earth science society
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• v.41 no.5
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• pp.478-489
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• 2020

This study presents an analysis of infrasonic signals from two accidental explosions in Gwangyang city, Jeonnam Province, Korea, on December 24, 2019, recorded at 12 infrasound stations located 151-435 km away. Infrasound propagation refracted at an altitude of ~40 km owing to higher stratospheric wind in the NNW direction, resulting in favorable detection at stations in that direction. However, tropospheric phases were observed at stations located in the NE and E directions from the explosion site because of the strong west wind jet formed at ~10 km. The transmission losses on the propagation path were calculated using the effective sound velocity structure and parabolic equation modeling. Based on the losses, the observed signal amplitudes were corrected, and overpressures were estimated at the reference distance. From the overpressures, the source energy was evaluated through the overpressure-explosive charge relationship. The two explosions were found to have energies equivalent to 14 and 65 kg TNT, respectively. At the first explosion, a flying fragment forced by an explosive shock wave was observed in the air. The energy causing the flying fragment was estimated to be equivalent to 49 kg or less of TNT, obtained from the relationship between the fragment motion and overpressure. Our infrasound propagation modeling is available to constrain the source energy for remote explosions. To enhance the confidence in energy estimations, further studies are required to reflect the uncertainty of the atmospheric structure models on the estimations and to verify the relationships by various ground truth explosions.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.61.2-61.2
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• 2009

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.98-112
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• 2000

Discrimination between natural earthquakes and man-made explosions is very essential but critical matter in Seismology. In the CTBT Monitoring business, this is very crucial issue and sometimes could occur the international conflict. In this study, we analyzed seismic and infrasound data from Chulwon Seismo-Acoustic Array and would like to introduce routine data processing procedures at the Korea Institute of Geology, Mining and Materials(KIGAM) to discriminate the earthquakes and artificial explosions. We found analyzing acoustic data together with seismic data is very effective way to identify and discriminate man made explosion from natural earthquake. Recent earthquakes in and around the Korean Peninsula are concentrated in a narrow zone with N60-70$^{\circ}$W in southern Korea, and Pyungan and Hwanghae Province in northern Korea. The mechanism of 14 larger earthquakes in and around the Korean Peninsula since 1936 show predominant strike-slip faulting together with minor thrust component. This indicates horizontal compression is dominant in and around the Korean Peninsula.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.59-63
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• 2002

Artificial blasts, defined as seismo-acoustic events, were discriminated from natural earthquakes in the Korean Peninsula by analyzing seismo-acoustic data. 219 seismo-acoustic events corresponding to 9 percent of total seismic events in 2001 were analyzed and classified as artificial surface blasts. Most seismo-acoustic events were concentrated in several areas. This distribution pattern was similar to the previous result in 1999-2000. Most of seismo-acoustic events especially concentrated at 7 small areas in North and South Korea. The number of seismo-acoustic events occurred in North and South Korea was 79 and 140 events, respectively. The local magnitude of seismic events from North Korea was relatively larger than from South. And some infrasound occurred from North Korea had a characteristic of sequential arrivals of signals, which reflected the different propagation in the atmosphere.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.315-318
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• 2008

Numerical calculation for the 1MW class horizontal axis wind turbine blade has been carried out to estimate the magnitude between discrete noise and random noise. Farassat formula 1A was adopted to get the discrete noise signal, and blade element momentum theory was used to obtain the distribution of the aerodynamic data along the blade span. Fukano's approach was also adopted to calculate the unsteady aerodynamic random noise due to the Karman vortex generation at the trailing edge of the wind turbine blade. From the noise prediction for the 1MW class horizontal axis wind turbine, the frequency band of the discrete noise lies in the infrasound region, and that of the random noise lies in the audible band region.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1183-1186
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• 2007

The low frequency noise, including infra-sound is known to affect human physiology and psychology. Guidelines and measurement method of low frequency noise has been introduced in several countries in order to evaluate low frequency noise. In this work, low frequency noise characteristics of dump truck was investigated in terms of the noise level and spectrum. The interior sound pressure level of the dump truck was between 60 and 105 dB in the frequency range of $1{\sim}250$ Hz.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.367-369
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• 1989

An infrasonic wide band transducer fabricated by polyvinylidenefluoride[PVDF] is studied experimentally. The sensitivity of transducer is fixed -53[dB] at frequency range from $10^{-2}$[Hz] to 2[Hz] and fixed -42[dB] range from 10[Hz] to 400[Hz] respectively. The resonance frequency of the element is 14[Hz], which is accord with the mechanical resonance frequency 25.5 [Hz]. We conjecture that the element is applicable to acoustics, communication system,seismological observation and other similiar fields.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.725-730
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• 2012

In this paper, flow noise characteristics of Savonius-type vertical-axis wind turbines are numerically investigated using hybrid CAA techniques. High frequency harmonics as well as BPF components are identified in the predicted noise spectra from a Savonius wind turbine. As the BPF components belong to infrasound, the higher harmonic components affects human response dominantly. Further analysis is performed to investigate the reason causing the higher frequency harmonic noise by changing operational conditions of a Savonius wind turbine. Based on this result, it is revealed that the frequency of higher harmonic components is determined by the radius of blades and angular velocity of Savonius wind turbine.