• 한국통신학회논문지
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• 제33권3C호
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• pp.255-261
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• 2008

3차원 물체에 대한 디지털 홀로그램을 합성할 때 사용되는 기존의 LT(look-up table) 방식은 고속연산은 가능하나 과도한 데이터 저장 공간을 요구하는 단점을 가지고 있다. 따라서 본 논문에서는 기존의 LT 방식의 연산속도는 그대로 유지하면서도 데이터 저장용량을 획기적으로 줄여줄 수 있는 새로운 룩업테이블 방식인 N-LT(novel look-up table) 제시하였다. 즉, 제안된 방식에서는 기존 LT 방식에서와 같이 3차원 물체의 모든 방향의 포인트가 아닌 각 깊이 방향의 포인트에 대한 요소 프린지 패턴만을 저장하고, 그 깊이 평면에 존재하는 포인트들의 프린지 패턴은 요소 프린지 패턴을 이동시켜 계산하게 된다. 실험 결과 제안된 N-LT 방식은 기존의 광선추적(ray-tracing) 방식에 비해 48.7배의 속도향상을 갖고, 기존의 LT 방식에 비해 1/217 정도의 데이터 공간이 필요함이 분석되었다.

• The Journal of the Acoustical Society of Korea
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• 제16권2E호
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• pp.3-13
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• 1997

The Jing is a traditional Korean percussion instrument which plays a major role in Korean folk music. The distingishing feature of this instrument is its unique, long lasting low tone timbre. In this paper, we investigated the vibro-acoustic characteristics of the Jing. Our attention was focused mainly on findings out the physical variables that determine its unique sound. By understanding the way in which the Jing is manufactured, we were able to realize that the unique manufacturing and especially the tuning process by expert craftsman is responsible for the peculiar timbre the Jing produces. The experimental methods implemented to analyzer the Jing were planar acoustic holography and direct measurements by accelerometers. The results from the holographic method and the direct measurements were in good agreement. It turned out that unlike most percussion instruments which have inharmonic partials, the Jing has harmonic partials which are responsible for its unique low-tone timbre. From the holographic representations of the modes, it is clear that the antinodes are located in the center of the Jing which is coincident with the typical striking location. In addition, intensity maps were constructed so that the specific acoustic energy flow can be visualized. It was also interesting to see the the circulation of energy intensity which corresponds to the rotating mode of the Jing.

• 한국전기전자재료학회논문지
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• 제13권9호
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• pp.791-795
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• 2000

Amorphous chalcogenide glasses have a wide variety of light-induced effects. In this study, we have investigated the diffraction efficiency of chalcogenide. As$_{40}$ Ge$_{10}$ Se$_{15}$ S$_{35}$ thin films by the various applied electric fields. The holographic grating in these thin films has been formed using a linearly polarized He-Ne laser light (633nm). The diffraction efficiency was investigated the two method of applied electric field in the perpendicular and parallel to the direction of inducing beam. We obtained that properties of diffraction efficiency in the two methods of applied electric field. The result is shown that the diffraction efficiency of parallel electric field is 285% increase, η=1.1$\times$10$^{-3}$ and the diffraction efficiency of perpendicular electric field is 80% decrease, η=9.83$\times$10$^{-5}$ . Also, we have investigated the anisotropy property on chalcogenide thin films by the electric field effects.

• 한국음향학회지
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• 제20권2호
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• pp.86-92
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• 2001

소음원 위치와 방위를 규명하기 위해 다양한 배열처리기술이 발전되어 왔다. 배열처리기술의 기본은 두 개의 수신센서에 수신된 신호의 시간차를 이용하여 소음원의 위치와 방위를 구하는 것으로 응용분야나 신호처리방법에 따라 고유의 특성을 갖는 빔형성기법, 상관함수기법 및 NAH (Near-Field Acoustic Holography) 등이 있다 본 연구에서는 이러한 기법들 중 광대역 소음원 탐지에 적용되는 상관함수기법을 채택하여 소음원의 대역폭과 측정 잡음원 간의 상관 관계가 위치나 방위 탐지 정확도에 미치는 영향을 분석하여 효과적인 소음원 탐지기법을 제안한다. 본 연구에서 채택한 배열의 기하학적 형상은 위치나 방위의 3차원적 모호성을 없애기 위한 3차원 비선형이며 제안된 기법의 타당성은 수치모의 실험 및 실제 실험으로 검증되었다.

• 한국산학기술학회논문지
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• 제12권5호
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• pp.2011-2018
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• 2011

본 논문에서는 공조용 로타리 컴프레서에서 발생하는 소음을 줄이기 위하여 음향 홀로그래피를 이용하는 방법을 다룬다. 소음이 방사되는 것을 음향 홀로그래피를 이용하여 정상적인 컴프레서와 문제가 있는 컴프레서에 대하여 측정하였다. 음향 홀로그램은 2가지 컴프레서의 다수의 격자점에서 측정 및 예측하였고, 컴프레서 표면 위로 재구성하였다. 2개의 마이크로폰을 사용하여 1344개의 측정 점에서 측정을 수행하였고, 그 중 1개의 마이크로폰은 스캐닝용이고 또 다른 하나의 마이크로폰은 레퍼런스용이다. 음향 홀로그래피는 소음원을 그래픽적으로 보여주기 위한 좋은 도구이다. 본 논문에서 컴프레서의 표면에서 소음 원 위치를 정확히 찾을 수 있었고, 그 소음원은 소음을 발생시키는 부품과 관계된 것이었다. 음향 홀로그래피는 가전제품에 대해 소음 저감 방법으로서 유용함을 알 수 있다.

• 소음진동
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• 제6권6호
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• pp.835-842
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• 1996

To identify the locations and strengths of acoustic sources, one may use a microphone line array. Apparent advantage of the source identification method utilizing a line array is that it requires less measurement points than intensity method and holography. This method is based on the information of magnitude and phase difference between pressure signals at each microphone. Since those differences are dependent on the source model, we have to assume them such as plane, monopole, etc. In this paper the conventional source identification methods such as beamforming method and MUSIC method are briefly reviewed by modeling a source as plane and spherical wave, then a modified method is introduced. This can be applied to sound field which may by either coherent or incoherent. Typical simulations and experiment are performed to confirm this identification method.

• 소음진동
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• 제3권2호
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• pp.163-167
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• 1993

Suction and discharge valves of special type refrigerant compressor are designed by finite element method for effective valve design development procedure. It is well known that valve dynamic characteristics, for example, the natural frequencies and vibration modes, are necessary for the computer simulation of compressor valve dynamics, the analysis of flow patterns, noise, impact stresses and their propagation phenomena. This paper has analysed the natural frequencies and vibration modes for the first three orders under the given special boundary conditions and the experiments are conducted by laser holography. And also stress distribution is analysed and experiment by strain gage is followed.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 1호
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• pp.293-296
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• 1999

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.324-329
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• 2003

An air-conditioner has various noise sources such as cooling fan noise, pumping noise, flow noise and impact noise. Among these, impact noise is the most unpleasant source. This is because the noise is produced in indoor unit of air-conditioner. To control the noise source effectively, first we must identify the noise sources. When we identify impact noise source, the measurement have to be carried out simultaneously. So we use beamforming method that requires less measurement points than intensity method and acoustic holography. The objective of this paper is to estimate the location of impact source. This objective can be achieved by using minimum variance cepstrum that is able to detect impulse embedded in noise. In this study, modified beamforming method based on cepstrum domain is proposed. Then this method applied to air-conditioner noise sources which produce impact noise.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1375-1378
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• 2009

In this paper, a new method to efficiently generate the holographic news ticker in holographic 3DTV or 3-D movies using N-LUT method is proposed. The proposed method is largely consisted of five steps: construction of the LUT for each character, extraction of characters in news ticker, generation and shift of the CGH pattern for news ticker using the LUT, composition of hologram pattern for 3-D video and news ticker and reconstruct the holographic 3D video with news ticker. From some simulation results confirmed the feasibility of the proposed method in fast generation of CGH patterns for holographic news ticker.