• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.158-158
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• 2017

비닐포장 하부에 위치한 콩의 생장 초기에 발생한 초엽을 인식하기 위한 연구를 수행중이다. 선행 연구에서 비닐포장에 접촉한 콩 초엽으로 인해 비닐포장 상부 표면의 열 반응 분포에 변화가 있음을 발견하였다. 현장에서 주행 중에 콩 초엽의 위치를 실시간으로 인식하고 연동된 선형 또는 회전형 엑츄에이터를 제어하여 정확한 위치에 천공을 수행하기 위해서는 계측 시스템과 제어 시스템간의 시간적 차이를 최소할 수 있는 실시간 신호 처리 기술이 필수적이다. 선행 연구에서 사용한 다중 IR 센서의 분해능은 $16{\times}4pixel$이며 주파수는 3 Hz로, 폭이 30cm 내외인 비닐포장 상부의 정밀 분석에 한계가 있음을 발견하였다. 이를 해결하기 위하여 분해능과 계측 주기를 개선할 수 있는 초소형 ($1cm{\times}1cm{\times}1cm$) 열화상 센서를 이용하였다. LWIR(Longwave infrared)영역에 해당하는 $8{\mu}m{\sim}14{\mu}m$의 영역에서 $0.05^{\circ}C$의 분해능을 보이는 $ Lepton^{TM}$ (500-0690-00, FLIR, Goleta, CA)모델을 사용하였다. 프레임당 $80{\times}60$ 픽셀의 정보가 2 Byte의 단위로 계측이 되며 9 Hz의 주파수로 대상면의 열 분포를 측정할 수 있다. 이론적으로 초당 정보 전송량은 86,400 Byte ($80{\times}60{\times}2{\times}9$)이며, 1 m를 진행하는 주행형 천공기에 적용할 경우 1 프레임당 10cm 정도의 면적을 측정하므로, 최대 위치 판정 분해능은 약 10 cm / 60 pixel = 0.17 cm/pixel로 상대적으로 정밀한 위치 판별이 가능하다. $80{\times}60{\times}2Byet$의 정보를 0.1초 이내에 분석해야 하는 기술적 과제를 해결하기 위하여 천공 작업기에 적합한 상용 SBC(Single board computer)의 클럭 속도(1 Ghz)로 처리 가능한 공간 분포 분석 알고리즘을 개발하였다. 전체 이미지 도메인을 한 번에 분석하는데 소요되는 시간을 최소화하기 위하여 공간정보 행렬을 균등히 배분하고 별도의 프로세서에서 Feature를 분석한 후 개별 프로세서의 결과를 경합식으로 판정하는 기술을 연구하였다. 오픈 소스인 MPICH(www.mpich.org) 라이브러리를 이용하여 개발한 신호 분석 프로그램을 클러스터링으로 연동된 개별 코어에 설치/수행 하였다. 2D 행렬인 열분포 정보를 공간적으로 균등 분배하여 개별 코어에서 행렬의 Spatial domain analysis를 수행하였다. $20{\times}20$의 클러스터링 단위를 이용할 경우 총 12개의 코어가 필요하였으며, 초당 10회의 연산이 가능함을 확인하였다. 병렬 클러스터링 기술을 이용하여 1m/s 내외의 주행 속도에 대응이 가능한 비닐포장 상부 열 분포 분석 시스템을 구현하였다.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.5
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• pp.197-206
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• 2014

Motor imagery based Brain-computer Interface(BCI), which has recently attracted attention, is the technique for decoding the user's voluntary motor intention using Electroencephalography(EEG). For classifying the motor imagery, event-related desynchronization(ERD), which is the phenomenon of EEG voltage drop at sensorimotor area in ${\mu}$-band(8-13Hz), has been generally used but this method are not free from the performance degradation of the BCI system because EEG has low spatial resolution and shows different ERD-appearing band according to users. Common spatial pattern(CSP) was proposed to solve the low spatial resolution problem but it has a disadvantage of being very sensitive to frequency-band selection. Discriminative filter bank common spatial pattern(DFBCSP) tried to solve the frequency-band selection problem by using the Fisher ratio of the averaged EEG signal power and establishing discriminative filter bank(DFB) which only includes the feature frequency-band. However, we found that DFB might not include the proper filters showing the spatial pattern of ERD. To solve this problem, we apply a band-selection process using CSP feature vectors and linear discriminant analysis to DFBCSP instead of the averaged EEG signal power. The filter selection results and the classification accuracies of the existing and the proposed methods show that the CSP feature is more effective than signal power feature.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.3
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• pp.355-362
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• 2015

Purpose: To investigate the effects of the transmittance of diffusive blurson visual acuity and contrast sensitivity. Methods: Visual acuity and contrast sensitivity were measured by using Optec$^{(R)}$ 6500 in Healthy 30 subjects aged $22.83{\pm}0.50$ (male 13, female 17) who were recruited from university students. Cataract simulator was used as a tool for diffusive blur. Visual acuity and contrast sensitivity were measured with varying the transmittance of diffusive blur in order to simulate progression of cataract and concentration in fog. Results: Visual acuity was reduced proportionally with decreasing the transmittance of the diffusive blur as follows: $VA(T)=1.84{\times}10^{-2}T-0.645$. Contrast sensitivity was decreased in all spatial frequencies. Contrast sensitivity in a high spatial frequency band was a greater effect and was off the normal range of contrast sensitivity. The peak of contrast sensitivity was moved in the direction to low frequency. From an intersection point of contrast sensitivity function, we could calculated the transmittance of the diffusive blur being off the normal range and the shift to peak spatial frequency. The peak of contrast sensitivity function was observed to move from 6 to 3 cpd at transmittance of about 78.70%, the contrast sensitivities for all frequencies at transmittance of about 69.71% were deviated from the normal range. Conclusions: The transmittance of diffusive blur causes a reduction in visual acuity and contrast sensitivity, a deviation of normal range of contrast sensitivity, and a shift of peak contrast sensitivity. Therefore the more attention is required when suffering from cataracts or driving in fog.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.166-173
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• 2014

A noncontact nondestructive testing (NDT) method is proposed to detect the damage of pipeline structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND: YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using three dimensional Fourier transformation (3DFT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a pipeline structures is conducted using the damage-sensitive features. Finally, the pipes with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.2
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• pp.268-274
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• 2016

To find the location of a random noise source present in the three-dimensional space is required at least four microphones. Using four microphones distributed in a three-dimensional space, noise source imaging technique was applied and evaluated on their performance. To compensate resolution problem which comes from both the position of the sensor array is fixed and the sampling frequency is low, up-sampling technique and interpolation function were applied. Five different interpolation methods were applied such as zero-padding, zero-order hold, first-order hold, spline function, and random signal padding. The up-sampling rate were chosen by two, four, eight times, and counting up 16 times. As a result, it was possible to more accurately estimate the position of the noise source according to the higher of the up-sampling rate. It also found that the first-order hold and the spline function's performance were slightly falling relative to other methods.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.169-184
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• 2024

This study investigates acoustic emission (AE) and micro-deformation characteristics of circular openings through biaxial compression experiments. The experimental results showed a significant increase in the frequency, count, energy, and amplitude of AE signals immediately before damage occurred in the circular opening. The differences in frequency and count between before and after damage initiation were significantly pronounced, indicating suitable factors for identifying damage occurrence in circular openings. The results for digital image correlation (DIC) technique revealed that micro-deformation was concentrated around the openings, as evidenced by the spatial distribution of strain. In addition, spalling was observed at the end of the experiments. The AE and micro-deformation characteristics presented in this study are expected to serve as fundamental data for evaluating the stability of underground openings and boreholes for deep subsurface projects.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.4
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• pp.21-26
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• 2016

In this paper we proposed a new structure of spatial combining power amplifier working in 60GHz global unlicensed band(56-64GHz) for the backhaul in the 5 generation mobile systems. The proposed structure is suitable to realize an antipodal finline transition in millimeter wave band, in which the size of cross section of waveguide becomes about a few mm ${\times}$ a few mm, due to its compact structure of the transition and shows effective heat sinking characteristics because its ground plane can contact to the body metal. However, the HFSS simulation results showed the return loss improvement by 1.27dB and the same insertion loss of -1.65dB compared with the conventional structure, which said nevertheless the advantages, there was no deterioration in the performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.2
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• pp.152-162
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• 2008

This paper presents a sliding mode controller (SMC) to directly control the active and reactive powers of a doubly ffd induction generator (DFIG) for wind turbines. Sliding-mode control (SMC) and space-vector modulation (SVM) are combined to ensure high-performance operation. SMC scheme is designed to provide robust and fast power controls without frame transformation and current controller used in the conventional FOC drive. Simulation results and experimental results demonstrate that proposed methods preserve the effectiveness and robustness during variations of active and reactive power.

• Journal of Korea Multimedia Society
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• v.8 no.4
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• pp.516-524
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• 2005

In this paper, a new watermarking scheme based on the POCS theory and human visual system is proposed. Using the POCS theory, watermarks are embedded into imperceptible image regions such as edge and strong texture area in the spatial domain. Also it is inserted into middle frequency band in the transform domain to achieve the robustness against compression and filtering, etc. In addition, different gain factors are employed into blocks classified by considering texture masking effect. By doing so, the proposed method has a novel property of having both the imperceptibility and the robustness simultaneously. Simulation results show that the proposed method has an excellent performance better than conventional approaches.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.70-71
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• 2002

연소실의 세장비(aspect ratio)가 작으면서 추진제의 고 충전을 이용한 단시간 연소 모타는 유도탄의 사출 모타 용으로 사용될 수 있다. 사출 모타는 일반적으로 모타 무게에 대한 제약 조건이 까다롭지 않기 때문에 무게 경량화에 대한 부담은 줄어들지만, 모타의 부피가 커지면 유도탄 발사 장치의 부피가 커지기 때문에 공간적인 측면에서 가능한 작게 하는 것이 시스템 전체의 효율을 증대시킬 수 있다. 또한 사출 모타의 연소 시간이 짧기 때문에(1초 이내) 추진제의 웹 두께가 작으므로 연소실의 주어진 공간에서 추진제를 많이 채우기 위한 방법으로 원통 튜브형 그레인을 여러 개의 다발로 사용하는 방법이 효과적이다. 이러한 관점에서 사출 모타용으로 다발 원통 튜브형 그레인을 설계/제작/연소시험을 하였더니 작은 저주파(약 10Hz)의 연소 불안정 현상이 발생하였다. (그림1). 이러한 주파수 대역은 일반적으로 잘 알려진 연소 불안정 모드 (longitudinal, tangential, and radial mode)와는 다른 아주 특이한 현상이다. 이러한 현상의 주 원인은 연소실 내 압력의 비평형에 의한 현상이라 판단되어 다음과 같은 연구를 수행하였다. 1) 그레인 튜브간의 압력 평형을 원활하게 하기 위하여 그레인에 구멍(홀)을 뚫어서 연소 안정화에 미치는 영향에 대한 연구(그림2), 2) 그레인에 홀을 뚫지 않고 격자와 격자간의 공간을 이용하여 그레인 간에 발생된 저주파의 압력 진동을 산란/소멸 시키는 연소 안정화 연구(그림3).