• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.244-246
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• 2005

The Tonpiltz transducer is one of the essential elements in sonar application. The characteristics of transducer depend on the piezoelectric ceramics and mechanical elements such as head mass, tail mass, pre-stress rod and so on. One of the important characteristics is stable electric resistance for high power transmitting operation. This paper presents characteristics variation of the underwater acoustic transducer with material variation of electric decoupler.

• 한국음향학회지
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• 제34권1호
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• pp.20-35
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• 2015

수중음향 전달채널의 임펄스 응답(Channel Impulse Response: CIR)은 음속구조(Sound Speed Profile: SSP)의 영향을 받으며, 채널 임펄스 응답의 변화는 수중음향통신 시스템의 성능에 중요한 영향을 미친다. 음속분포의 변화는 단기간 내에서도 나타날 수 있으며, 수중음향 모뎀 설계 시 반드시 고려되어야 한다. 이 논문은 2013년도에 제주도 동방해역에서 수행된 JACE13에서 취득된 데이터를 기반으로 음선전달 수치해석을 통해 단기간 동안 시간에 따라 변화하는 음속구조가 음향 신호 전달에 미치는 영향을 통계적으로 분석한 결과를 제시한다. 분석결과 송 수신기 수심별로 채널 임펄스 응답의 변화가 다양하게 나타나며, 송 수신기 수심이 깊을수록 음속구조의 변동에 따른 음향신호 전달 양상의 변화는 작아지고, 신호 준위가 높게 나타난다. 이 연구에서의 다양한 거리, 송, 수신기 수심에 따라 얻어진 채널 임펄스 응답 추정 결과는 수온약층에서의 하방굴절로 인한 연속된 해저면 반사와 작은 해저면 반사손실이 장거리 신호 전파에 중요한 요인이 될 수 있음을 보여주며, 시변동성을 갖는 해양환경에서의 수중 음향 통신은 시간에 따라서 성능이 충분히 달라질 수 있다는 것을 보여준다.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2000년도 종합학술발표회 논문집 Vol.10 No.1
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• pp.95-98
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• 2000

Film bulk acoustic resonator used in microwave region can be analyzed by one-dimension Mason's model and one-dimensional numerical method, but it had several constraints to analyze effects of area variation, electrode-area variation, electrode-shape variation and spurious characteristics. To overcome these constraints film bulk acoustic resonator must be analysed by three dimensional numerical method. So, in this paper three dimensional finite element method was used to analyze several moles of resonance and was compared with the one dimension Mason's model analysis and analytic solution.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.351-366
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• 2016

Macroperforations improve the sound absorption performance of porous materials in acoustic cavities and in waveguides. In an acoustic cavity, enhanced noise reduction is achieved using porous materials having macroperforations. Double porosity materials are obtained by filling these macroperforations with different poroelastic materials having distinct physical properties. The locations of macroperforations in porous layers can be chosen based on cavity mode shapes. In this paper, the effect of variation of macroporosity and double porosity in porous materials on noise reduction in an acoustic cavity is presented. This analysis is done keeping each perforation size constant. Macroporosity of a porous material is the fraction of area covered by macro holes over the entire porous layer. The number of macroperforations decides macroporosity value. The system under investigation is an acoustic cavity having a layer of poroelastic material rigidly attached on one side and excited by an internal point source. The overall sound pressure level (SPL) inside the cavity coupled with porous layer is calculated using mixed displacement-pressure finite element formulation based on Biot-Allard theory. A 32 node, cubic polynomial brick element is used for discretization of both the cavity and the porous layer. The overall SPL in the cavity lined with porous layer is calculated for various macroporosities ranging from 0.05 to 0.4. The results show that variation in macroporosity of the porous layer affects the overall SPL inside the cavity. This variation in macroporosity is based on the cavity mode shapes. The optimum range of macroporosities in poroelastic layer is determined from this analysis. Next, SPL is calculated considering periodic and nodal line based optimum macroporosity. The corresponding results show that locations of macroperforations based on mode shapes of the acoustic cavity yield better noise reduction compared to those based on nodal lines or periodic macroperforations in poroelastic material layer. Finally, the effectiveness of double porosity materials in terms of overall sound pressure level, compared to equivolume double layer poroelastic materials is investigated; for this the double porosity material is obtained by filling the macroperforations based on mode shapes of the acoustic cavity.

• 한국분무공학회지
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• 제18권3호
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• pp.126-131
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• 2013

This paper describes the effect of ultrasonic frequency(f) on the atomization and deformation characteristics of single water droplet in an acoustic levitation field. To achieve this, the ultrasonic levitator that can control sound pressure and velocity amplitude by changing frequency was installed, and visualization of single water droplet was conducted with high resolution ICCD and CCD camera. At the same time, atomization and deformation characteristics of single water droplet was studied in terms of normalized droplet diameter($d/d_0$), droplet diameter(d) variation and droplet volume(V) variation under different ultrasonic frequency(f) conditions. It was revealed that increase of ultrasonic frequency reduces the droplet diameter. Therefore, it is able to levitate with low sound pressure level. It also induces the wide oscillation range, large diameter and volume variation of water droplet. In conclusion, the increase of ultrasonic frequency(f) can enhance the atomization performance of single water droplet.

• 말소리와 음성과학
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• 제2권4호
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• pp.19-28
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• 2010

The purpose of this study was to increase the current understanding of the acoustic characteristics of voices with advancing age. The relationship between age-related changes in body physiology and certain acoustic characteristics of voice was studied in a sample of 80 men representing four chronological age groupings (20-29, 50-59, 60-69, 70-79) who were all of good physical condition. Each subject was asked to phonate the vowel /a/, /i/, and /u/ for as long as possible at comfortable frequency and intensity level and read the sentence. A promising voice analysis program (Multi-Dimensional Voice $Program^{TM}$) was used to measure the fundamental frequency ($f_0$), jitter, shimmer, $f_0$ variation, peak-amplitude variation, smoothed pitch perturbation quotient, smoothed amplitude perturbation quotient, soft phonation index, $f_0$-tremor intensity index, amplitude tremor intensity index, and noise-to-harmonics ratio from the samples.

• 한국음향학회지
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• 제34권4호
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• pp.257-263
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• 2015

음향 공명 이론을 이용하여 단일층 원통형 껍질 속 내부 물질의 음향 식별을 연구하였다. 원통형 껍질의 이론적인 공명 피크 주파수들은 내부 물질의 밀도 변화에 의해서는 거의 영향을 받지 않으나, 음속 변화에 의해서는 두드러지게 변화를 보인다. 이와 같은 음향 의존성을 원통형 껍질 속 내부 물질을 식별하는 데 활용할 수 있다. 단일층 원통형 껍질에 대한 음향 공명 스펙트로그램을 정규화 주파수 및 내부 물질 음속의 함수로서 이론적으로 작성한다. 이 스펙트로그램에 측정한 후방 산란 음압장의 음향 공명 피크들을 중첩함으로써 내부 물질을 음향학적으로 식별할 수 있다. 이를 실험적으로 확인하기 위하여 물, 기름 또는 에틸렌글리콜을 넣은 원통형 껍질의 후방 산란 음압장을 수조 안에서 측정하였다. 단일 송수신 방식으로 중심주파수 1.05 MHz인 음파 변환기로 측정한 후방 산란 음압장의 음향 공명 피크로 내부 물질을 식별할 수 있었다.

• 한국소음진동공학회논문집
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• 제21권11호
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• pp.1059-1066
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• 2011

The micro-perforated panel absorber(MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high(around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• 말소리와 음성과학
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• 제3권3호
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• pp.77-88
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• 2011

Foreign accent in second language production depends heavily on the transfer of features from the first language. This study examines acoustic variations in segments and suprasegments by native and nonnative speakers of English, searching for patterns of the transfer and plausible indexes of foreign accent in English. The acoustic variations are analyzed with recorded read speech by 20 native English speakers and 50 Korean learners of English, in terms of vowel formants, vowel duration, and syllabic variation induced by stress. The results show that the acoustic measurements of vowel formants and vowel and syllable durations display difference between native speakers and nonnative speakers. The difference is robust in the production of lax vowels, diphthongs, and stressed syllables, namely the English-specific features. L1 transfer on L2 specification is found both at the segmental levels and at the suprasegmental levels. The transfer levels measured as groups and individuals further show a continuum of divergence from the native-like target. Overall, the eldest group, students who are in the graduate schools, shows more native-like patterns, suggesting weaker foreign accent in English, whereas the high school students tend to involve larger deviation from the native speakers' patterns. Individual results show interdependence between segmental transfer and prosodic transfer, and correlation with self-reported proficiency levels. Additionally, experience factors in English such as length of English study and length of residence in English speaking countries are further discussed as factors to explain the acoustic variation.

• 대한후두음성언어의학회지
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• 제9권2호
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• pp.142-146
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• 1998

Background : It has been established that the fundamental frequency(Fo) of the vowels varies systemically as a function of vowel height. Specifically, high vowels have a higher Fo than low vowels. Two major explanations or hypotheses dominate contemporary accounts of fired to explain the mechanisms underlying intrinsic variation in vowel Fo, source-tract coupling hypothesis and tongue-pull hypothesis. Objectives : Total laryngectomy surgery necessiates removal of all structures between the hyoid bone and the tracheal rings. Therefore, the assumption that no direct interconnection exists between the tongue and pharyngoesophageal segment that would mediate systematic variation in vowel Fo appears quite reasonable. If tongue-pull hypothesis is correct, systemic differences in Fo between high versus low vowels produced by esophageal speakers would not Or expected. We analyzed the Fo in the vowels of esophageal voice. Materials and method : The subjects were 11 cases of laryngectomee patients with fluent esophageal voice. The five essential vowels were recorded and analyzed with computer speech analysis system(Computerized Speech Lab). The Fo was measured using acoustic waveform, automatically and manually, and narrow band spectral analysis. Results : The results of this study reveal that intrinsic variation in vowel Fo is clearly evident in esophageal speech. By analysis using acoustic waveform automatically, the signals were too irregular to measure the Fo precisely. So the data from automatic analysis of acoustic waveform is not logical. But the Fo by measuring with manually calculated acoustic waveform or narrowband spectral analysis resulted in acceptable results. These results were interpreted to support neither the source-tract coupling nor the tongue-pull hypotheses and led us to offer an alternative explanation to account for intrinsic variation of Fo.