• 대한의용생체공학회:의공학회지
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• 제26권1호
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• pp.31-35
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• 2005

A novel synthetic aperture method for real-time three-way dynamic focusing is proposed, which provides lateral beam patterns represented as the product of Fourier transforms of transmit subaperture, receive subaperture, and a synthetic window function. In the proposed method, all array elements are fired individually and for each firing echo signals are recorded from all elements of a receive subaperture moving along an array with the transmit element. The three-way dynamic focusing is then achieved by employing a synthetic aperture algorithm for two-way dynamic focusing and a synthetic focusing method for transmit dynamic focusing. Both theoretical analysis and computer simulation results show that the proposed method produces ultrasound beams with improved lateral resolution at all depths compared to the conventional phased array imaging and synthetic aperture focusing methods.

• Agricultural and Biosystems Engineering
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• 제3권1호
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• pp.35-43
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• 2002

The spectral color resolution of an image is very important in color image analysis. Two factors influencing the spectral color resolution of an image are illumination intensity and lens aperture for a selected vision system. An optimal combination of illumination intensity and lens aperture for color image analysis was determined in the study. The method was based on a model of dynamic range defined as the absolute difference between digital values of selected foreground and background color in the image. The role of illumination intensity in machine vision was also described and a computer program for simulating the optimal combination of two factors was implemented for verifying the related algorithm. It was possible to estimate the non-saturating range of the illumination intensity (input voltage in the study) and the lens aperture by using a model of dynamic range. The method provided an optimal combination of the illumination intensity and the lens aperture, maximizing the color resolution between colors of interest in color analysis, and the estimated color resolution at the combination for a given vision system configuration.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1164-1167
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• 2009

Motion-image-quality of LCD-TVs is discussed by dynamic spatial frequency response. Smaller temporal aperture or higher frame rate can improve dynamic response, but an increase of motion velocity easily cancels the improvement. A guideline for deciding the desirable temporal aperture and frame rate of LCD-TVs is described, under the condition that camera and display have the same parameters. Two candidates of the desirable parameter sets will be (240 or 300 Hz, 50 to 100% aperture) and (120Hz, 25 to 50% aperture), from the viewpoint of "limit of acceptance" on motion-imagequality-deterioration for critical picture materials.

• 대한의용생체공학회:의공학회지
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• 제22권4호
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• pp.321-330
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• 2001

In this paper, we propose a new synthetic aperture focusing scheme for improving the lateral resolution which is one of the most important factors determining the quality of ultrasound imaging. The proposed scheme enables full round-trip dynamic focusing with approximately limited property. This properties are obtained through transmitting plane waves of which the traveling angle varies with the receive subaperture position, as opposed to stepping the spherical wave source across an array in other synthetic aperture focusing schemes, and employing dynamic focusing in receive. In this paper, the properties of the proposed scheme is analyzed in which a hypothetical infinite line source is used to transmit the plane waves and verified through computer simulation results. Also, we show that the proposed scheme is realizable with an array transducer with a finite aperture size. In summary, it is shown through comparison between the field contours of the proposed scheme and the conventional scheme that the proposed scheme can improve greatly the lateral resolution of ultrasound imaging.

• 대한전자공학회논문지SD
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• 제41권7호
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• pp.37-41
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• 2004

We have formulated an empirical analytic model for the static characteristics of implanted vertical-cavity surface-emitting lasers (VCSELs). Specifically, we have derived analytic formulas for the threshold current, slope efficiency, dynamic resistance, and the output power and forward voltage at the operation current of 12 ㎃ in terms of the implant and metal-aperture radii by fitting the measured results. The radii of the metal aperture and implant mask of the 850 nm VCSELs range from 4 to 12.5 ${\mu}{\textrm}{m}$ and 7 to 17.5 ${\mu}{\textrm}{m}$ respectively. The model shows the way of tailoring the VCSEL characteristics by changing the mask dimensions only.

• 대한의용생체공학회:의공학회지
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• 제20권4호
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• pp.503-513
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• 1999

본 논문에서는 일반적인 합성구경기법에 대한 통합 모형을 제시하고 수학적인 해석을 통하여 합성구경 기법들에 대한 초음파 빔패턴의 단일 표현식을 유도하였다. 이 결과를 이용하여 기존의 합성구경 기법들에 대한 성능을 분석하고 비교하였으며, 선형주사 영상에 적합한 새로운 합성구경 기법을 제안하였다. 제안된 방법은 모든 영상점에서 양방향 동적 집속이 가능하며, 이를 실제 영상에 적용하여 의료용 초음파 B-모드 영상의 해상도를 획기적으로 개선할 수 있다. 제안된 방법에 의하여 집속된 초음파 빔패턴은 기존의 방식과 비교하여 주엽의 폭이 절반으로 감소하고 측엽의 크기는 유사하다. 컴퓨터 모사실험을 통하여 본 논문의 해석결과와 제안된 합성구경 기법의 타당성을 검증하였다.

• 말소리와 음성과학
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• 제10권4호
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• pp.77-89
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• 2018

Speech articulators are coordinated for the purpose of segmental constriction in terms of a task. In particular, vertical jaw movements repeatedly contribute to consonantal as well as vocalic constriction. The current study explores vertical jaw movements in conjunction with bilabial constriction in bilabial stop /p/ in the context /a/-to-/a/. Revisiting kinematic data of /p/ collected using the electromagenetic midsagittal articulometer (EMMA) method from seven (four female and three male) speakers of Seoul Korean, we examined maximum vertical jaw position, its relative timing with respect to the upper and lower lips, and lip aperture minima. The results of those dependent variables are recapitulated in terms of linguistic (different word boundaries) and paralinguistic (different speech rates) factors as follows. Firstly, maximum jaw height was lower in the across-word boundary condition (across-word < within-word), but it did not differ as a function of different speech rates (comfortable = fast). Secondly, more reduction in the lip aperture (LA) gesture occurred in fast rate, while word-boundary effects were absent. Thirdly, jaw raising was still in progress after the lips' positional extrema were achieved in the within-word condition, while the former was completed before the latter in the across-word condition. Lastly, relative temporal lags between the jaw and the lips (UL and LL) were more synchronous in fast rate, compared to comfortable rate. When these results are considered together, it is possible to posit that speakers are not tolerant of lenition to the extent that it is potentially realized as a labial approximant in either word-boundary condition while jaw height still manifested lower jaw position in the across-word boundary condition. Early termination of vertical jaw maxima before vertical lower lip maxima across-word condition may be partly responsible for the spatial reduction of jaw raising movements. This may come about as a consequence of an excessive number of factors (e.g., upper lip height (UH), lower lip height (LH), jaw angle (JA)) for the representation of a vector with two degrees of freedom (x, y) engaged in a gesture-based task (e.g., lip aperture (LA)). In the task-dynamic application toolkit, the jaw angle parameter can be assigned numerical values for greater weight in the across-word boundary condition, which in turn gives rise to lower jaw position. Speech rate-dependent spatial reduction in lip aperture may be able to be resolved by means of manipulating activation time of an active tract variable in the gestural score level.

• 대한원격탐사학회지
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• 제33권4호
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• pp.437-444
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• 2017

Since land pixels often generate false alarms in ship detection using Synthetic Aperture Radar (SAR), land masking is a necessary step which can be processed by a land area map or water database. However, due to the continuous coastline changes caused by newport, bridge, etc., an updated data should be considered to mask either the land or the oceanic part of SAR. Furthermore, coastal concrete facilities make noise signals, mainly caused by side lobe effect. In this paper, we propose two methods. One is a semi-automatic water body data generation method that consists of terrain correction, thresholding, and median filter. Another is a dynamic land masking method based on water database. Based on water database, it uses a breadth-first search algorithm to find and mask noise signals from coastal concrete facilities. We verified our methods using Sentinel-1 SAR data. The result shows that proposed methods remove maximum 84.42% of false alarms.

• 대한의용생체공학회:의공학회지
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• 제23권2호
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• pp.87-99
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• 2002

본 논문에서는 대상테의 움직임이 합성구경 기법에 미치는 영향을 조사하고, 이를 토대로 합성구경 기법의 움직임 긱함을 극복할 수 있는 방법을 제안하였다. 제안한 방법은 일정한 관심영역 내에서 대상테의 대표적인 축방향 움직임을 추정하고 이에 의한 집속 지연 오타만을 관심영역의 모든 영상점에 대하여 동일하게 보상하는 영역 기반의 움직임 보상 기법을 사용한다. 이때 대표 움직임은 관심영역 내에서 접속된 신호의 에너지가 최대가 되는 점에서의 움직임을 상호상관을 이용하여 계산할 수 있다. 또한 자기상관 기반의 도플러 평균 주파수 추정 기법을 이용하여 관심영역 내의 대표적인 축방향 움직임(대표 움직임 속도)을 추정하는 방법을 제안하였다. 모의 실험과 실제 인체 실험 결과 두 방법 모두 합성구경 영상의 움직임 오류를 제거함으로써 양방향 동적접속의 구현을 가능하게 하여 초음파 영상의 해상도 및 SNR을 현저히 개선시킬 수 있음을 확인하였다. 또한 자기상관 방법은 훨씬 적은 계산량으로 상호상관 방법과 거의 동일한 성능을 제공함을 확인하였다.

• 대한의용생체공학회:의공학회지
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• 제23권6호
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• pp.419-430
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• 2002

본 논문에서는 양방향 화소단위 집속 기법을 희박 어레이 기법을 사용하여 효율적으로 구현하는 방법에 대해 제안한다. 제안한 방법은 각 주사선을 구성할 때 합성에 이용되는 부구경 사이의 간격을 멀리함으로써 적은 수의 부구경으로 큰 크기의 합성구경을 형성하여 시스템의 복잡도를 감소시키면서 초음파 영상의 해상도와 프레임율을 향상시키게 된다. 하지만 이때 합성에 사용되는 부구경 사이의 간격 증가로 인해 그레이팅 로브 값은 상승하게 된다. 이러한 그레이팅 로브는 일반적인 합성구경 기법에서는 제거할 수 있다. 하지만 본 논문에서는 일반적인 합성구경 기법과는 달리 양방향 화소단위 집속 기법에서는 부구경 사이의 간격이 클 경우 발생하는 그레이팅 로브를 제거할 수 없음을 이론적으로 해석하였다. 또한 이러한 그레이팅 로브 값을 송신 집속점을 근거리에 위치시키고 합성에 사용되는 부구경간의 간격을 수신부구경의 크기에 비례하여 적절히 선택함으로써 의료용 초음파 영상에 적합한 -40dB 이하로 억제하는 방법과 조건을 제시하였다. 모의 생체와 실제 인체 실험 결과 제안한 방법을 통해 보다 적은 수의 부구경을 이용하여 더욱 빠른 프레임율의 양방향 화소단위 집속 기법의 구현이 가능함을 확인하였다