• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.606-611
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• 2008

The objective of the present study is to actively control the flame oscillation in the experimental lean premixed methane burner by the phase-controlled sound waves. The authors propose the methodology of generating the phase-controlled sound waves by directly sensing the preferential frequency and generating the sensor-triggered sound waves with fixed optimum phase difference with the flame oscillation. The real-time controller is implemented in the present study, and the combustion noise reduction is achieved. The reduction is 20dB at peak frequency and 13dB in the OASPL.

• 한국전자파학회논문지
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• 제25권5호
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• pp.542-547
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• 2014

1차 사용자(primary user)는 자신에게 할당된 대역을 사용하여 통신을 수행하는데, 이때 송신 신호의 전력은 대부분 해당 대역에 집중되어 있지만, 일부는 인접 대역으로 넘어간다. 이 때문에 인접 대역이 비어 있더라도 오경보율이 예상보다 크게 발생할 수가 있다. 이전 연구 중에 인접 대역 누설 현상이 스펙트럼 센싱에 미치는 영향을 분석한 것이 있지만, 이때 페이딩을 고려하지 않았다. 본 논문에서는 페이딩 채널 환경에서 인접 대역 누설이 에너지 기반 스펙트럼 센싱 성능에 미치는 영향을 검파 확률과 오경보 확률 측면에서 분석하고자 한다.

• 전기전자학회논문지
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• 제24권3호
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• pp.719-726
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• 2020

능동형 유기 발광 다이오드의 픽셀 노화를 보상하기 위한 문턱 전압 감지 회로가 제안된다. 제안된 문턱 전압 감지 회로는 샘플-홀드 회로와 10비트의 해상도를 가지는 단일 입력 축차 근사형 아날로그-디지털 변환기로 구성된다. 각 샘플-홀드 회로의 스케일 다운 변환기와 단일-차동 변환기를 가지는 가변 이득 증폭기를 제거하기 위해 단일 입력 축차 근사형 아날로그-디지털 변환기를 위한 중간 기준 전압 보정과 입력 범위 보정이 수행된다. 제안된 문턱 전압 감지 회로는 1.8V 공급 전압의 180nm CMOS 공정을 사용하여 설계된다. 단일 입력 축차 근사형 아날로그-디지털 변환기로의 유효 비트와 전력 소모는 각각 9.425비트와 2.83mW이다.

• 한국재료학회지
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• 제24권3호
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• pp.152-158
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• 2014

We report the effect of the fabric of the surface microstructure on the CO gas sensing properties of $SnO_2$ thin films deposited on self-assembled Au nanodots ($SnO_2$/Au) that were formed on $SiO_2/Si$ substrates. We characterized structural and morphological properties, comparing them to those of $SnO_2$ thin films deposited directly onto $SiO_2/Si$ substrates. We observed a significant enhancement of CO gas sensing properties in the $SnO_2$/Au gas sensors, specifically exhibiting a high maximum response at $200^{\circ}C$ and quite a low detection limit of 1 ppm level in dry air. In particular, the response of the $SnO_2/Au$ gas sensor was found to reach the maximum value of 32.5 at $200^{\circ}C$, which is roughly 27 times higher than the response (~1.2) of the $SnO_2$ gas sensor obtained at the same operating temperature of $200^{\circ}C$. Furthermore, the $SnO_2/Au$ gas sensors displayed very fast response and recovery behaviors. The observed enhancement in the CO gas sensing properties of the $SnO_2/Au$ sensors is mainly ascribed to the formation of a nanostructured morphology in the active $SnO_2$ layer having a high specific surface-reaction area by the insertion of a nanodot form of Au nucleation layer.

• 대한원격탐사학회지
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• 제40권1호
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• pp.45-56
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• 2024

Faced with aging populations, declining resources, and limited agricultural productivity, rural areas in South Korea require innovative solutions. This study investigated the potential of drone-based vegetation indices (VIs) to analyze soybean growth patterns in open-field smart agriculture in Goesan-gun, Chungbuk Province, South Korea. We monitored multi-seasonal normalized difference vegetation index (NDVI) and the normalized difference red edge (NDRE) data for three soybean lots with different irrigation methods (subsurface drainage, conventional, subsurface drip irrigation) using drone remote sensing. Combining NDVI (photosynthetically active biomass, PAB) and NDRE (chlorophyll) offered a comprehensive analysis of soybean growth, capturing both overall health and stress responses. Our analysis revealed distinct growth patterns for each lot. LotA(subsurface drainage) displayed early vigor and efficient resource utilization (peaking at NDVI 0.971 and NDRE 0.686), likely due to the drainage system. Lot B (conventional cultivation) showed slower growth and potential limitations (peaking at NDVI 0.963 and NDRE 0.681), suggesting resource constraints or stress. Lot C (subsurface drip irrigation) exhibited rapid initial growth but faced later resource limitations(peaking at NDVI 0.970 and NDRE 0.695). By monitoring NDVI and NDRE variations, farmers can gain valuable insights to optimize resource allocation (reducing costs and environmental impact), improve crop yield and quality (maximizing yield potential), and address rural challenges in South Korea. This study demonstrates the promise of drone-based VIs for revitalizing open-field agriculture, boosting farm income, and attracting young talent, ultimately contributing to a more sustainable and prosperous future for rural communities. Further research integrating additional data and investigating physiological mechanisms can lead to even more effective management strategies and a deeper understanding of VI variations for optimized crop performance.

• Smart Structures and Systems
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• 제20권3호
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• pp.273-283
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• 2017

This paper presents and compares three feedback control strategies for active control of noise inside a 3-D vibro-acoustic cavity. These are a) control strategy based on direct output feedback (DOFB) b) control strategy based on linear quadratic regulator (LQR) to reduce structural vibrations and c) LQR control strategy with a weighting scheme based on structural-acoustic coupling coefficients. The first two strategies are indirect control strategies in which noise reduction is achieved through active vibration control (AVC), termed as AVC-DOFB and AVC-LQR respectively. The third direct strategy is based on active structural-acoustic control (ASAC). This strategy is an LQR based optimal control strategy in which the coupling between the various structural and the acoustic modes is used to design the controller. The strategy is termed as ASAC-LQR. A numerical model of a 3-D rectangular box cavity with a flexible plate (glued with piezoelectric patches) and with other five surfaces treated rigid is developed using finite element (FE) method. A single pair of collocated piezoelectric patches is used for sensing the vibrations and applying control forces on the structure. A comparison of frequency response function (FRF) of structural nodal acceleration, acoustic nodal pressure, and piezoelectric actuation voltage is carried out. It is found that the AVC-DOFB control strategy gives equal importance to all the modes. The AVC-LQR control strategy tries to consume the control effort to damp all the structural modes. It is seen that the ASAC-LQR control strategy utilizes the control effort more intelligently by adding higher damping to those structural modes that matter more for reducing the interior noise.

• 대한원격탐사학회지
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• 제16권3호
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• pp.243-260
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• 2000

가시광 영역에서 해수의 원격반사($R_{rs}$)도 및 수출광(water leaving radiance: Lw) 스펙트럼 크기를 해수의 광 특성(흡광도; a, 역산란; $b_b$)에 영향을 가장 크게 미치는 3개 물질 즉, 클로로필, 무기성 부유입자, 용해유기물의 량으로 모델링 하였다. 모델은 간략하게 $R_{rs}$=0.046 $b_b$/(a+$b_b$)로 주어졌으며, 모델의 대상 해역은 광특성이 전혀 다른 적조 발생해역, 맑은 해수, 탁수해역으로 나우어 연구하였다. 모델로 얻어진 원격반사도는 형장 관측치와 스펙트럼의 모양, 값의 분포 및 기존의 해색 클로로필 알고리즘 등으로 비교하여 모델의 타당성을 검증하였다. 결과는 아주 다양한 광 특성을 같은 해양이라 하여도 본 연구의 모델은 거의 완벽하게 해색 스펙트럼, 원격반사도 혹은 water leaving radiance(Lw)를 재현할 수 있는 것으로 나타났다. 본 모델은 앞으로 OSMI와 같은 해색위성 알고리즘 개발, CASE-II water 알고리즘, neural network 알고리즘 개발에 크게 기여할 것으로 사료되며 그 외에도 해색 대기보정 모델 개발에서 대기 신호의 정밀 보정에 활용될 수 있을 것으로 기대된다.

• Journal of information and communication convergence engineering
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• 제8권2호
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• pp.238-243
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• 2010

CSD is Active RFID based Container Security Device which is proposed by the U.S Department of Home Security. It is mounted inside the container to sense opening of the container door. ConTracer is the CSD which is developed in this research whose major features are sensing door opening status as well as history inquiring on internal environment and shock to the container by mounting the temperature/ humidity/ shock sensors. Moreover, its RFID frequency bandwidth uses 433MHz and 2.4GHz to correspond actively to the frequency used by different countries. This paper introduces the development trend of CSD, compares the ConTracer which is developed thru this research and other company's CSD, and introduces CSD System which is designed and established using ConTracer. Finally, the implemented CSD System is verified by applying the demonstration service to container distribution between Korea and China.

• Smart Structures and Systems
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• 제3권2호
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• pp.201-217
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• 2007

An active damage detection technique is introduced to locate damage in an isotropic plate using Lamb waves. This technique uses a time-domain energy model of Lamb waves in plates that the wave amplitude inversely decays with the propagation distance along a ray direction. Accordingly the damage localization is formulated as a least-squares problem to minimize an error function between the model and the measured data. An active sensing system with integrated actuators/sensors is controlled to excite/receive $A_0$ mode of Lamb waves in the plate. Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the undamaged plate from the recorded signal of the damaged plate. In the experimental study, after collecting the scattered wave signals, a discrete wavelet transform (DWT) is employed to extract the first scattered wave pack from the damage, then an iterative method is derived to solve the least-squares problem for locating the damage. Since this method does not rely on time-of-flight but wave energy measurement, it is more robust, reliable, and noise-tolerant. Both numerical and experimental examples are performed to verify the efficiency and accuracy of the method, and the results demonstrate that the estimated damage position stably converges to the targeted damage.

• Smart Structures and Systems
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• 제12권5호
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• pp.547-577
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• 2013

To suppress vibration and noise of mechanical structures piezoelectric ceramics play an increasing role as effective, simple and light-weighted damping devices as they are suitable for sensing and actuating. Out of the various piezoelectric damping methods this paper compares mode based active control strategies to passive shunt damping for thin plates. Therefore, a new approach for the optimal placement of the piezoelectric sensors/actuators, or more general transducers, is proposed after intense theoretical investigations based on the Kirchhoff kinematical hypotheses of plates; in particular, modal and nilpotent transducers are discussed in detail. Based on the proposed distribution a discrete design for modal transducers is implemented, tested and verified on an experimental setup. For active control the modal sensors clearly identify the eigenmodes, whereas the modal actuators impose distributed eigenstrains in order to reduce the transverse plate vibrations. In contrast to the modal control, passive shunt damping works without requiring additional actuators or auxiliary power and can therefore act as an autonomous system, but it is less effective compensating the flexible vibrations. Exemplarily, an acryl glass plate disturbed by an arbitrary force initialized by a loudspeaker is investigated. Comparing the different methods their specific advantages are highlighted and a significant broadband reduction of the vibrations of up to -20dB is obtained.