• Journal of information and communication convergence engineering
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• 제20권1호
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• pp.22-30
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• 2022

The reinforcement learning algorithm has proven its potential in solving sequential decision-making problems under uncertainties, such as finding paths to route data packets in wireless sensor networks. With reinforcement learning, the computation of the optimum path requires careful definition of the so-called reward function, which is defined as a linear function that aggregates multiple objective functions into a single objective to compute a numerical value (reward) to be maximized. In a typical defined linear reward function, the multiple objectives to be optimized are integrated in the form of a weighted sum with fixed weighting factors for all learning agents. This study proposes a reinforcement learning -based routing protocol for wireless sensor network, where different learning agents prioritize different objective goals by assigning weighting factors to the aggregated objectives of the reward function. We assign appropriate weighting factors to the objectives in the reward function of a sensor node according to its hop-count distance to the sink node. We expect this approach to enhance the effectiveness of multi-objective reinforcement learning for wireless sensor networks with a balanced trade-off among competing parameters. Furthermore, we propose SDN (Software Defined Networks) architecture with multiple controllers for constant network monitoring to allow learning agents to adapt according to the dynamics of the network conditions. Simulation results show that our proposed scheme enhances the performance of wireless sensor network under varied conditions, such as the node density and traffic intensity, with a good trade-off among competing performance metrics.

• 콘크리트학회논문집
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• 제18권2호
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• pp.293-298
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• 2006

The reinforced concrete(RC) structures strengthened with fiber reinforced plastic(FRP) has been accepted by the construction engineering community for rehabilitation. FRP composites can present many advantages like a corrosion resistance, strength-weight ratio, relatively short application time, and cost effectiveness. The beams under design load, however, are cracked and result in degrading the strength. It is difficult to recognize cracks and deflections on the surface of the concrete members retrofitted with FRP through the life cycle. For these reasons, if they result in the effects, which were below the expected strength, we must monitor the state of concrete structures all the time in order to take an appropriate measure. Fiber Bragg Grating(FBG) sensor excel as monitoring of investigating the stress state of the retrofitted beams with FRP. The main objective of this study is to measure strain by experiment and analyze the behavior of RC beams retrofitted with FRP using FBG sensor. The kinds of FRP which were used in research are carbon, glass and improved hybrid FRP(IFRP) that has capacity than any other FRP. Other variables are the length of FRP, the number of sheet.

• Journal of Electrical Engineering and Technology
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• 제8권5호
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• pp.1056-1061
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• 2013

The widely used motors in HEV(Hybrid Electric Vehicles) are IPMSM(Interior Permanent Magnet Synchronous Motor) which has no rotor heat, higher efficiency and advantageous in volume and weight comparing with other motors. For vector control of IPMSM, position information of rotor is required but Resolver is mainly used as the detecting sensor. However, the use of position sensors will reduce the system reliability of hybrid electric vehicles. In this paper, a way to control the motor by sensorless was proposed at the event of sensor failure. We also implemented IPMSM sensorless operation by the expanded EMF(Electro Motive Force) voltage way and harmonic voltage which is applying in the low speed area. And we proposed how to change with sensorless control by detecting the position sensors failure and verified it through experiments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권5호
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• pp.1929-1950
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• 2020

Reliable and secure data transmission in the application environment assisted by the wireless sensor network is one of the major challenges. Problem like blind forwarding and data inaccessibility affect the efficiency of overall infrastructure performance. This paper proposes routing protocol for forwarding and error recovery during packet loss. The same is achieved by energy and hops distance-based formulation of the routing mechanism. The reachability of the intermediate node to the source node is the major factor that helps in improving the lifetime of the network. On the other hand, intelligent hop selection increases the reliability over continuous data transmission. The number of hop count is factor of hop weight and available energy of the node. The comparison over the previous state of the art using QualNet-7.4 network simulator shows the effectiveness of proposed work in terms of overall energy conservation of network and reliable data delivery. The simulation results also show the elimination of blind forwarding and data inaccessibility.

• 한국도로학회논문집
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• 제10권3호
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• pp.79-86
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• 2008

차량의 동적하중이 도로상에 작용하는 위치를 계측하기 위한 원더링 계측용 사선센서의 적정 설치각도를 제안하였다. 이를 위해서 테이프스위치 센서를 이용하여 원더링 계측용 장비를 개발하였고, 개발된 장비와 실험차량을 이용하여 평가용 자료를 수집하였다. 수집자료 분석 결과, 사선센서의 설치각도가 커질수록 원더링 수집자료의 오차가 감소하였고, 이러한 오차의 감소는 통계적으로도 의미가 있는 것으로 분석되었다. 그러나 사선센서를 $30^{\circ}$ 이상으로 설치할 경우, 탠덤축의 제원상의 이유로 인해 오류자료가 수집되는 것을 확인할 수 있었다. 따라서 본 연구에서는 국내 차량제원 등을 종합하여 원더링 계측용 사선센서의 적정 설치각도를 $20^{\circ}{\sim}25^{\circ}$로 제안하였다.

• 대한임베디드공학회논문지
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• 제8권5호
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• pp.273-283
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• 2013

The traditional medical equipments are devices used by medical professionals but not used in public environment. Common people, however, require light-weight medical devices to make healthcare for themselves nowadays. Those medical devices are used to monitor personal health status such as blood pulse, blood pressure, diabetes. Also, some of them are operated in mobile environment called u-healthcare. This paper implements a portable healthcare system composed of $SpO_2$(Saturation of Partial Pressure Oxygen) sensors and a gateway for detecting hypoxemia during people's leasure activity such as climbing or hiking. The $SpO_2$ sensor is designed as watch style to support dynamic exercise and the gateway is designed as necklace style to support the elderly. The result of a performance evaluation shows that the performance of the $SpO_2$ sensor using reflection technology is not lower than that of a clairvoyant styled $SpO_2$ sensor.

• Journal of Information Processing Systems
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• 제19권4호
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• pp.527-539
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• 2023

In the positioning algorithm of two-dimensional planar sensor array, the estimation error of time difference-ofarrival (TDOA) algorithm is difficult to avoid. Thus, how to achieve accurate positioning is a key problem of the positioning technology based on planar array. In this paper, a method of sensor reliability discrimination is proposed, which is the foundation for selecting positioning sensors with small error and excellent performance, simplifying algorithm, and improving positioning accuracy. Then, a positioning model is established. The estimation characteristics of the least square method are fully utilized to calculate and fuse the positioning results, and the non-uniform weighting method is used to correct the weighting factors. It effectively handles the decreased positioning accuracy due to measurement errors, and ensures that the algorithm performance is improved significantly. Finally, the characteristics of the improved algorithm are compared with those of other algorithms. The experiment data demonstrate that the algorithm is better than the standard least square method and can improve the positioning accuracy effectively, which is suitable for vibration detection with large noise interference.

• 센서학회지
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• 제11권4호
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• pp.209-217
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• 2002

광섬유 ROTDR (Rayleigh Optical Time Domain Reflectometry)을 이용하여 침입자를 높은 감도와 넓은 영역에서 탐지할 수 있는 매설형 광섬유 센서의 개발에 관한 실험을 수행하였다. 단위 길이당 넓은 면적을 감지 할 수 있는 매설형 광섬유 감지부를 설계 제작하고, 인가된 침입물체의 하중에 따른 신호특성을 고찰하였다. 일반 광통신용인 직경 1.5mm와 3.5mm인 광섬유를 길이 각각 4km를 사용하여 광섬유 굽힘손실을 발생시키는 침입감지 장치를 설계 제작하고, 상용 ROTDR의 조건설정은 파장 $1.55{\mu}m$, 거리범위 5km, 펄스폭 20 ns, S/N비가 5.7인 시스템으로 실험하였으며, 광섬유 RODTR 센서시스템의 측정신호로부터 침입자 신호를 찾아내기 위한 측정신호처리 시스템을 구성하였다. 광섬유 센서의 인가하중과 광손실값과의 관계는 거의 선형적으로 변함을 보였으며, 공간분해능은 2m로 측정되었고, 침입감지면적은 단위길이당 $1.3m^2$이고, 감도는 0.17dB/kg으로 외부 침입물체등을 감지하기에 충분히 높은 감도와 감지영역을 가짐을 알 수 있다.

• 한국지반공학회논문집
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• 제34권2호
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• pp.33-42
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• 2018

본 연구에서는 소형 압전소자의 전기-역학적 임피던스를 이용하여 모래의 단위중량이나 강도를 평가하였다. 다짐 몰드 내 크기가 다른 세 종류의 미고결 낙동강모래를 느슨하거나 조밀하게 성형한 다음 내부에 직경 20mm 원형모양의 납작한 압전소자를 설치하고 임피던스를 측정하였다. 또한, 가는 낙동강모래에 시멘트비 4, 8, 12, 16%로 직경 50mm, 높이 100mm의 고결 공시체를 6층으로 다져서 제작하였다. 고결 공시체의 3층 내부에 압전소자를 수평방향으로 설치한 다음 3일 동안 임피던스 신호를 측정하였으며, 측정 후 일축압축시험을 실시하였다. 미고결 모래의 단위중량이 증가함에 따라 공진주파수는 102kHz에서 105kHz까지 약간 증가하였으며, 공진주파수 발생 시 컨덕턴스는 감소하였다. 고결 모래의 양생시간과 시멘트비가 증가함에 따라 공진주파수는 129kHz에서 266kHz까지 크게 증가하였으며, 공진주파수 발생 시 컨덕턴스는 반대로 감소하는 경향을 보였다. 고결 모래의 일축압축강도는 시멘트비에 따라 289-1,390kPa 정도이며, 공진주파수와는 뚜렷한 정비례 관계를 보이지만 공진주파수 발생 시 컨덕턴스와는 반비례 관계를 보였다.

• 한국산학기술학회논문지
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• 제10권2호
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• pp.370-376
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• 2009

최근 USN 환경에서 다양한 센서 네트워크 활용 가능성이 높아지고 있다. 하지만 기존에 제안되었던 센서네트워크 라우팅 프로토콜들이 현실적으로 어려움 점이 있다. 본 논문에서는 대표적인 계층적 라우팅 프로토콜인 HEED가 가지는 생존성과 부분 클러스터 생성의 문제를 해결하고자 에너지 거리 가중치를 사용한 개선된 HEED 라우팅 프로토콜을 제안하고자 한다. 본 논문에서 제안한 개선된 HEED 프로토콜은 기존의 HEED보다 각 노드들의 잔존 에너지양과 거리 가중치를 두어 새로운 CH를 초기에 선정하고 선출된 CH노드의 잔존 에너지양이 50%가 되는 시점을 기준으로 교체해 주는 방식을 제안하였다. 이를 통해서 클러스터 내의 모든 노드들이 에너지 소비를 공평하게 함으로써 전체 클러스터의 생존율을 약 30% 가량 향상시킬 수 있었다. 또한 CH를 교체 선출함에 있어서도 응답시간을 기준으로 기존의 CH노드와 가장 가까운 곳에 위치하는 노드로 교체하도록 하는 기법을 적용하였다.