• Structural Monitoring and Maintenance
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• 제1권4호
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• pp.411-425
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• 2014

A relatively low frequency Lamb wave-based damage identification method called damage imaging method for rectangular composite plate is presented. A damage index (DI) is generated from the delay matrix of the Lamb wave response signals, and it is used to indicate the location and approximate area of the damage. The viability of this method is demonstrated by analyzing the numerical and experimental Lamb wave response signals from rectangular composite plates. The technique only requires the response signals from the plate after damage, and it is capable of performing near real time damage identification. This study sheds some light on the application of Lamb wave-based damage detection algorithm for plate-type structures by using the relatively low frequency (e.g., in the neighborhood of 100 kHz, more suitable for the best capability of the existing fiber optic sensor interrogator system with the sampling frequency of 500 kHz) Lamb wave response and a reference-free damage detection technique.

• 한국항해학회지
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• 제25권4호
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• pp.371-379
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• 2001

We have reported the new measurement system which was substituted digital filter for the analog filter in order to develop the optimal system that could find the time delay between each sensors with high accuracy. And also we have confirmed through the experiments that the accuracy of measurements were differentiated by the methods what kind of digital filter had been adopted. This paper suggests two algorithms which approximate the sound source's bearing and distance. One is that sound source's relative bearing can be approximately regarded as the gradient of hyperbolic asymptote, the other is that the source's range can be approximated under the condition of a long range source relative to the sensor's interval. And a series of experiments were carried out with the source's distance 22.42meters and the random bearing interval within the limits of $-90^{\circ}$~$+90^{\circ}$. As a result, we have recognized that the approximation methods could measure the bearing and distance with higher accuracy than the method using trigonometric relation could do.

• ETRI Journal
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• 제39권1호
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• pp.13-20
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• 2017

A method is proposed for scheduling sensor accesses to the shared network in a networked control system. The proposed method determines the access order in which the sensors are granted medium access through minimization of the state estimation error covariance. Solving the problem by evaluating the error covariance for each possible ordered set of sensors is not practical for large systems. Therefore, a convex optimization problem is proposed, which yields approximate yet acceptable results. A state estimator is designed for the augmented system resulting from the incorporation of the optimally chosen communication sequence in the plant dynamics. A car suspension system simulation is conducted to test the proposed method. The results show promising improvement in the state estimation performance by reducing the estimation error norm compared to round-robin scheduling.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.111-116
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• 2009

As an experimental technique to analyze the far-field characteristics of underwater cylindrical array sensors, cylindrical acoustic holography is studied. Inside an laboratory water tank, far-field directivity patterns as well as near-field source images are reconstructed from the measured hologram by hydrophone array. Approximate equation for far-field directivity estimation is derived based on stationary phase method. The simulation and experiment show well usefulness of the proposed method in application of underwater array sensors.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.905-908
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• 1988

In recent, Kalman filter technique has been much used as one of technique for tracking of the moving target. But some problem are still remained to be resolved. For example, when Kalman filter technique is applied to nonlinear system, the technique is nonoptimal estimator. Therefore, extended Kalman filter is proposed to reduce modeling error for nonlinear system. In this study, an extended Kalman filter in Cartesian coordinates is described for moving target, when the radar sensor measures range, azimuth and elevation angle in polar coordinates. And an approximate gain computation algorithm is proposed. In this approach, Kalman gains are computed for three uncoupled filter and multiplied by a Jacobian transformation determined from the measured target position and orientation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.819-821
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• 1998

This paper deals with a method or a residual generation for fault isolation in a centrifugal pump with a water circulation system, driven by a speed controlled dc motor. It is based on parity relations derived from the moving-average model of the system and is used to identify sensor faults and two possible brush and impeller faults, where the former is dealt with additive faults, while the latter characterized as discrepancies between the nominal and actual plant parameters of the system is modelled by multiplicative faults. We will represent the propagation of this uncertainty to the model matrices by the approximate handling of partial derivatives of polynomials. With multiplicative faults, the transformation matrix implemented in the residual generator are calculated on-line. The simulation studies demonstrate that small changes of the system can be detected and diagnosed by using the method.

• 한국통신학회논문지
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• 제41권11호
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• pp.1589-1597
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• 2016

본 논문에서는 사막, 해양과 같은 개활지역에서 모바일 센서 네트워크에서 사용하는 전력량을 감소시킬 수 있는 시스템을 제안한다. 무선 센서 네트워크에서 데이터 전송 전력 소모는 거리의 제곱에 비례하다는 특징이 있다. 따라서 배터리로 동작하는 모바일 센서의 위치가 센서 데이터를 수집하는 싱크 노드와 멀리 떨어져 있을 경우, 데이터를 전송하는데 요구되는 전력 사용량이 높아지게 되어 센서의 동작 시간이 짧아지는 문제가 발생한다. 이에 따라 본 논문에서는 기존 모바일 센서의 전송 가능 거리보다 짧은 전송 거리를 설정하여 센서가 해당 거리 이내에 존재할 때만 데이터를 보내게 함으로써 필요한 전력량을 감소시키는 시스템에 대하여 제안하였다. 뿐만 아니라, 싱크노드에서는 압축 센싱을 이용하여 센서로부터 수집한 데이터를 더 적은 전송 횟수로 게이트웨이에 전송함으로써 전체 네트워크의 에너지 효율을 증가시켰다. 본 논문에서 제안한 시스템은 라즈베리 파이와 아두이노를 이용하여 실제로 구현하였으며, 싱크노드로부터 적은 데이터를 수신하여도 게이트웨이에서 원 데이터와 매우 근사적으로 복호가 가능함을 실험을 통하여 확인하였고 실제 실험 환경에서 제안된 시스템의 성능을 이론적으로 검증하였다.

• 한국통신학회논문지
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• 제38B권1호
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• pp.63-71
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• 2013

무선 센서 네트워크에서 이동 싱크 그룹은 같은 임무를 수행하기 위해 지리적으로 공통적인 움직임을 가지며 동일한 데이터를 필요로 한다. 이들 그룹에 데이터를 전달하기 위해서는 이동 싱크 그룹의 현재 위치를 파악하고, 이를 소스에게 제공하는 기법이 중요해진다. 기존 연구에서는 영역 정보를 제공하기 위해 플러딩을 사용하여 모든 멤버 싱크들을 포함하는 영역을 계산하고 이 정보를 소스에게 전달하였다. 그러나 멤버 싱크들의 위치를 수집하기 위해 영역 안에서 매번 주기적으로 수행되는 플러딩과 소스로의 위치 업데이트는 에너지 소모 측면에서 상당한 오버헤드이다. 본 논문에서는 주기적인 플러딩과 위치 업데이트 없이 에너지 효율적으로 이동 싱크 그룹을 지원하는 방안을 제안한다. 제안 방안은 플러딩 없이 싱크 그룹의 고유한 성질을 이용하여 멤버 싱크 일부의 움직임으로 그룹 전체의 움직임을 근사하여 그룹의 위치를 계산할 수 있다. 또한, 제안 방안에서는 무선 통신 환경의 오버히어링(overhearing) 특성을 활용한 역전파 학습 방법으로 소스로의 지속적인 위치 업데이트 비용 없이 위치 정보를 전달한다. 시뮬레이션 결과는 이전 연구에 비해 에너지 소모 측면에서 상당히 개선되었음을 보여준다.

• Journal of the Optical Society of Korea
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• 제17권3호
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• pp.231-236
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• 2013

We present both theoretically and experimentally the thermo-optic characteristics of micro-structured optical fiber (MOF) filled with mixed liquid. The performance of MOF depends on the efficient interaction between the fundamental mode of the transmitted light wave and the tunable thermo-optic materials in the cladding. The numerical simulation indicates that the confinement loss of MOF presents higher temperature dependence with higher air-filling ratios $d/{\Lambda}$, longer incident wavelength and fewer air holes in the cladding. For the 4cm liquid-filled grapefruit MOF, we demonstrate from experiments that different proportions of solutions lead to tunable temperature sensitive ranges. The insertion loss and the extinction ratio are 3~4 dB and approximate 20 dB, respectively. The proposed liquid-filling MOF will be developed as thermo-optic sensor, attenuator or optical switch with the advantages of simple structure, compact configuration and easy fabrication.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권3호
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• pp.1204-1227
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• 2020

The tradeoff between energy conservation and traffic balancing is a dilemma problem in Wireless Sensor Networks (WSNs). By analyzing the intrinsic relationship between cluster properties and long distance transmission energy consumption, we characterize three node sets of the cluster as a theoretical foundation to enhance high performance of WSNs, and propose optimal solutions by introducing rendezvous and Mobile Elements (MEs) to optimize energy consumption for prolonging the lifetime of WSNs. First, we exploit an approximate method based on the transmission distance from the different node to an ME to select suboptimal Rendezvous Point (RP) on the trajectory for ME to collect data. Then, we define data transmission routing sequence and model rendezvous planning for the cluster. In order to achieve optimization of energy consumption, we specifically apply the economic theory called Diminishing Marginal Utility Rule (DMUR) and create the utility function with regard to energy to develop an adaptive energy consumption optimization framework to achieve energy efficiency for data collection. At last, Rendezvous Transmission Algorithm (RTA) is proposed to better tradeoff between energy conservation and traffic balancing. Furthermore, via collaborations among multiple MEs, we design Two-Orbit Back-Propagation Algorithm (TOBPA) which concurrently handles load imbalance phenomenon to improve the efficiency of data collection. The simulation results show that our solutions can improve energy efficiency of the whole network and reduce the energy consumption of sensor nodes, which in turn prolong the lifetime of WSNs.