• 한국음향학회지
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• 제9권2호
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• pp.5-13
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• 1990

본 연구에서는 수 파장 이상의 깊이에 존재하는 결함을 탐상하기 위하여 50MHz의 중심주파수에서 동작하는 small aperture형 초음파현미경을 구성하였고 다층구조 샘플에 대한 영상을 연구분석하였다. 다층구조물에서의 출력특성을 음향감쇠, 수차, 렌즈형태, 샘플의 특성에 영향을 받으며 이것은 다층구조 I.C.와 bonding층 탐상에 이용할 수 있다. 실험결과, small aperture형 초음파현미경은 large aperture형 시스템에 비하여 두꺼운 샘플의 탐상에 유리하며 타 도구에서 관찰이 어려운 다층구조의 층별 탐상과 내부구조의 변형상태등을 2차원 영상으로 탐상할 수 있는 유용한 도구임을 확인하였다.

• 한국음향학회지
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• 제34권5호
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• pp.343-350
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• 2015

본 논문에서는 프로펠러 공동에 의해 발생하는 광대역 선박방사소음의 방향성에 대한 연구를 수행했다. 국외 및 한국 근해에서 측정된 선박방사소음 자료의 조사를 통해 국내외 실험 자료에서 공통적으로 수중방사소음의 선수-선미 비대칭 방향성이 관찰되는 것을 재확인했다. 이 비대칭의 원인을 찾기 위해, 국내의 수중방사소음 측정에 사용된 상선과 동일한 형상에 대해 경계요소법을 이용한 수치해석을 적용했다. 수치해석 결과는 선박에 의한 소음의 회절효과가 선박방사소음에서 선수-선미의 비대칭 방향성이 나타나는 주된 원인이라는 것을 강하게 시사한다.

• 한국음향학회지
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• 제39권6호
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• pp.585-591
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• 2020

적응형 전송 기법은 수중 음향 채널의 상태에 따라 전송 파라미터를 변경하여 전송 및 성능을 향상 시키는 효율적인 방법이다. 본 논문에서는 적응형 전송 기법에서 전송 모드를 결정하기 위한 네 가지 모드와 이의 모드를 검출하기 위한 세 가지 임계값 검출 알고리즘을 제안한다. 송신기에서 정보비트의 크기를 자유롭게 설정하기 위하여 컴볼루션 부호를 사용하였으며, 수신기에서는 성능을 향상시키기 위하여 BCJR 복호 기반 터보등화기법을 적용하였다. 또한 수중 실험을 통해 각 모드에서 성능을 만족하는 임계값 간의 관계를 분석하였다.

• 한국해양공학회지
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• 제28권5호
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• pp.429-439
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• 2014

The target echoes contain information on the target such as the orientation, kinematics, and internal structure, as well as the external geometrical shape of the target. In addition, the pattern of the target echoes depends on the arrangement of the transmitters and receivers in space. Therefore, the study of the target echoes in a multi-static SONAR system can be useful for detecting and tracking submerged objects using an underwater surveillance system. For this purpose, an acoustic measuring system for multi-static target echoes was designed and tested in an acoustic water tank. Some preliminary data are presented and discussed.

• Smart Structures and Systems
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• 제19권2호
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• pp.195-202
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• 2017

The aim of this paper is to develop a novel method to determine the severity of a damage in a thin plate. This paper presents a novel fault detection and diagnosis approach employing a new electromagnetic acoustic transducer, called EMAT, together with a complex signal processing method. The method consists in the recognition of a fault that exists within the structure, the fault location, i.e. the identification of the geometric position of damage, and the determining the significance of the damage, which indicates the importance or severity of the defect. The main scientific novelties presented in this paper is: to develop of a new type of electromagnetic acoustic transducer; to incorporate wavelet transforms for signal representation enhancements; to investigate multi-parametric analysis for noise identification and defect classification; to study attenuation curves properties for defect localization improvement; flaw sizing and location algorithm development.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.183-188
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• 2005

본 연구에서는 기상 압력파동에 구속된 액적 내부의 에너지 파동과 연소응답의 상관관계를 고찰하였다. SRK 상태방정식과 Flash 계산법에 기초한 1차원 액적 기화모델로 기상과 액상의 2상 시스템에 대한 수치해석을 수행하였다. n-Pentane 액적과 기체 질소를 대상으로 기상압력과 압력파동 구동주파수에 따른 에너지 파동의 전파특성을 분석하였다. 액적 내부 에너지 파동의 주파수가 낮을수록 액적 내부로의 에너지 전파가 용이하였으며 결과적으로 연소응답의 크기를 감소시키는 요인이 되었다.

• 말소리와 음성과학
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• 제1권4호
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• pp.3-9
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• 2009

Acoustically English vowels are defined primarily by formant values. The measurements of the values have been usually made at a few time points of the vowel segment despite the fact that the majority of English vowel formants vary dynamically throughout the segment. This study attempts to collect acoustic data of the nine English vowels published by Hillenbrand et al. (1995) online and to examine the acoustic features of the English vowels for phoneticians and English teachers. The author used Praat to obtain the data systematically at six equidistant timepoints over the vowel segment. Obvious errors were corrected based on the spectrographic display of each vowel. Results show that the first two formant trajectories are important to separate the nine vowels within the front- or back-vowel groups. The third formant trajectories appear comparable except those of the high vowels. Second, the back vowels leave longer traces on the vowel space toward the locus of the following consonant /d/. Third, each vowel has inherent duration, pitch, and intensity patterns. The results match the findings of Yang (2009). From the results, the author concludes that dynamic spectral changes are important in specifying acoustic characteristics of English vowels. Further studies on the application of the vowel trajectories to English pronunciation lessons or on perceptual experiment of synthesized vowels are desirable.

• 말소리와 음성과학
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• 제2권3호
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• pp.75-80
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• 2010

The present research investigated the characteristics of voice between genders and nationalities by measuring the acoustic parameter values of Korean and Chinese students. Sound Forge was used to collect voice samples and Praat was used to measure and analyze jitter, shimmer, NHR, $sF_0$, and pitch range. The results of this research are a follows. First, during prolongation of the vowels, there was no significant difference in $F_0$ between Korean and Chinese males and Korean and Chinese females. Korean males and females had higher $F_0$ values than Chinese males and females. Secondly, during sentence reading, there was no significant difference between Korean and Chinese males in $sF_0$. But between female groups, there was a significant difference in $sF_0$. Thirdly, during sentence reading, the pitch range in Korean males was found to be narrower compared to Korean and Chinese females who had wider pitch range, showing a significant difference. Fourthly, jitter in the five vowels /a, i, u, e, o/ was found to be higher in Chinese than Korean subjects. In the vowels /a, e, u/ females were higher than males showing a significant difference. Fifthly, shimmer in the vowels /a, e, u/ was found to be higher in Chinese than Korean subjects showing a significant difference. Finally, NHR in the vowels /a, u, o/ was found to be higher in Chinese than Korean subjects showing a significant difference.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2003년도 제27회 추계학술대회
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• pp.53-53
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• 2003

For evaluating the feasibility of treating recurrent lesions in the vaginal cuff and cervix by hyperthermia, ultrasound applicators were designed, constructed, and characterized. For the treatment A half-cylindrical transducer Cd=1cm, length=lcm) and cylindrical transducer (d=2.5cm, length= 1.5cm) were used to construct ovoid type and cylindrical applicators. For the ovoid type applicator, each element was operated at 1.5MHz and characterized by measuring transducer efficiency and acoustic power distribution. Thermocouple probes were used to measure the temperature rise in phantom. The element sizes used in this study were selected to be comparable for high dose rate brachytherapy colpostat applicator. Each element was powered separately to achieve a desired temperature pattern in a target. The acoustic output power as a function of applied electric power of the element 1 and 2 was linear over this 1 to 40 W range and efficiencies were 32.2${\pm}$3.4% and 46.2${\pm}$0.8%, respectively. The temperature measurements in phantom showed that 6$^{\circ}C$ temperature rise was achieved at 2 cm from the applicator surface. As a conclusion, the ability of the ultrasound colpostat applicator to be used for hyperthermia was demonstrated by measuring acoustic output power, ultrasound field distribution, and temperature rise in phantom. Based on the characteristics of this applicator, it has the potential to be useful for inducing hyperthermnia to the vaginal cuff in clinic.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1597-1604
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• 2005

The identification of a moving noise source is important in reducing the source power of the transport systems such as airplanes or high speed trains. However, the direct measurement using a microphone running with noise source is usually difficult due to wind noise, white the source motion distorts the frequency characteristics of the pass-by sound measured at a fixed point. In this study the relationship between the spectra of the source and the pass-by sound signal is analyzed for an acoustic source moving at a constant velocity. Spectrum of the sound signal measured at a fixed point has an integral relationship with the source spectrum. Nevertheless direct conversion of the measured spectrum to the source spectrum is ill-posed due to the singularity of the integral kernel. Alternatively a differential equation approach is proposed, where the source characteristics can be recovered by solving a differential equation relating the source signal to the distorted measurement in time domain. The parameters such as the source speed and the time origin, required beforehand, are also determined only from the frequency-phase relationship using an auxiliary measurement. With the help of the regularization method, the source signal is successfully recovered. The effects of the parameter errors to the estimated frequency characteristics of the source are investigated through numerical simulations.