• Journal of information and communication convergence engineering
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• v.20 no.1
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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.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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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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• v.8 no.5
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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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• v.14 no.5
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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.

• International Journal of Highway Engineering
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• v.10 no.3
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• pp.79-86
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• 2008

This paper proposed the appropriate installation angle of skewed sensors for measuring vehicle wandering data, which are collected to figure out the location of dynamic weight of a moving vehicle on roadways. We developed a device using tape-switch sensors and a computer program and collected vehicle wandering data with the device and probe vehicles. As a result, the steeper the skewed sensor was installed, the lower the error was shown. However, we could not collect proper data when a skewed sensor was set up higher than $30^{\circ}$ due to tandem axle. Therefore, this study suggested the appropriate angle of skewed sensors as a degree of $20^{\circ}$ to $25^{\circ}$ for gathering wandering data.

• IEMEK Journal of Embedded Systems and Applications
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• v.8 no.5
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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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• v.19 no.4
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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.

• Journal of Sensor Science and Technology
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• v.11 no.4
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• pp.209-217
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• 2002

The developing of buried fiber optic sensor with high sensitivity and broad-area detecting intruders is carried out using fiber optic ROTDR(Rayleigh Optical Time Domain Reflectometry). The sensing part was designed to be able to broad-area detect intrusion effect per optical fiber length under ground. The bending light losses in optical fibers are investigated by commercial mini ROTDR with wavelength $1.55{\mu}m$, distance range 5km, pulse width 20ns, SNR=5.7. The sensing fibers are selected as the common telecommunication fibers are the 1.5mm, 3.5 mm outer diameter, 4km each length fiber products. Experiments were investigate the characteristics of signal sensitivity according to applied intrusion weight. The relation between the applied weight and the bending loss was almost linear, and broad-area detect intrusion effects are the 2m resolution and $1.3m^2$ per optical fiber length respectively. The light loss by the applied weight on fiber was 0.17 dB/kg. that the sensitivity of the optical fiber sensor was sufficient to detect intruders passing over the buried optical fiber.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.33-42
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• 2018

In this study, the EMI (electro-mechanical impedance) of a small piezoelectric sensor was applied for measuring a unit weight and cementation (strength) of sand. Three different sizes of uncemented Nakdong River sand were filled loosely or densely into a compaction mold. A piezoelectric sensor with 20 mm in diameter was installed within sand for impedance measurement. A small Nakdong River sand was mixed with cement ratios of 4, 8 12, 16% and then compacted into a specimen with 50 mm in diameter and 100 mm in height. The specimen consisted of 6 layers with a sensor at the third layer. The impedance signals for 3 days and unconfined compressive strength at the 3rd day were measured. As the unit weight of uncemented sand increased, the resonant frequency increased slightly from 102 to 105 kHz but a conductance at resonant frequency decreased. For cemented sands, as the curing time and cement ratio increased, the resonant frequency increased significantly from 129 to 266 kHz but the conductance at resonant frequency decreased. The unconfined compressive strength (UCS) of cemented sands was between 289 and 1,390 kPa for different cement ratios. The relationship of UCS and resonant frequency linearly increased but one with a conductance at resonant frequency was in inverse proportion.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.2
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• pp.370-376
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• 2009

Recently, Study for routing protocol is gone vigorously in the Ubiquitous Sensor Network. A hierarchical routing protocol is being practical and received interest among them. Therefore we analyze a weak point of HEED. And I suggest the new protocol that solved a weak point of HEED. The new protocol that we propose puts weight in the energy remainder amount than HEED and elect CH. And elected CH is designed to change by new node when quantity of energy leftover becomes less than 50%. Therefore all nodes come to use energy fairly. The protocol that we proposed can prove the cluster survival rate about 30%. And CH is more effective because when elect CH replace, response time selects small node.