• Journal of Sensor Science and Technology
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• v.29 no.6
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• pp.369-373
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• 2020

A hydrogen sensor was fabricated by utilizing a bundle of metal oxide nanostructures whose growth positions were selectively controlled by utilizing graphene, which is a carbon of atomic-unit thickness. To verify the reducing ability of graphene, it was confirmed that the multi-composition metal oxide V₂O₅ was converted into VO₂ on the graphene surface. Because of the role of graphene as a reducing catalyst, it was confirmed that ZnO and MoO₃ nanostructures were grown at high density only on the graphene surface. The fabricated gas sensor showed excellent sensitivity.

• Journal of Sensor Science and Technology
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• v.19 no.5
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• pp.369-374
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• 2010

It is important to efficiently elect the cluster header in Hierarchical Sensor Network, because it largely affects on the lifetime of the network. Therefore, recent research is focused on the lifetime extension of the whole network for efficient cluster header election. In this paper, we propose the new Cluster Header Election Scheme in which the cluster is divided into Group considering Distance from Upper Node, and a cluster header will be elected by node density of the Group. Also, we evaluate the performance of this scheme, and show that this proposed scheme improves network lifetime in Zigbee environment.

• Journal of the Optical Society of Korea
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• v.17 no.4
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• pp.312-316
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• 2013

A novel fiber-optic sensor system is suggested in which fiber Bragg grating sensors are demodulated by a wavelength-sweeping fiber laser source and a spectrometer. The spectrometer consists of a diffraction grating and a 512-pixel photo-diode array. The reflected Bragg wavelength information is transformed into spatial intensity distribution on the photo-diode array. The peak locations linearly correspond to the Bragg wavelengths, regardless of the nonlinearities in the wavelength tuning mechanism of the fiber laser. The high power density of the fiber laser enables obtaining high signal-to-noise ratio outputs. The improved demodulation characteristics were experimentally demonstrated with a fiber Bragg grating sensor array with 5 gratings. The sensor outputs were in much more linear fashion compared with the conventional tunable band-pass filter demodulation. Also it showed advantages in signal processing, due to the high level of photo-diode array signals, over the broadband light source system, especially in measurement of fast varying dynamic physical quantities.

• Journal of Korean Association for Spatial Structures
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• v.19 no.1
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• pp.101-108
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• 2019

Recently, measuring instruments for SHM of structures has been developed. In general, the wireless transmission of sensor signals, compared to its wired counterpart, is preferable due to the absence of triboelectric noise and elimination of the requirement of a cumbersome cable. However, the low-cost wireless MEMS sensor has high noise density and transmits the signal wirelessly, so data transmission delay occurs during measurement. Therefore, the footbridges that was previously measured by a mobile phone in 2014 was remeasured using G-Link-200, iPad and iPhone to compare their performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.5
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• pp.662-665
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• 2020

Energy Efficiency in any WSN (Wireless Sensor Network) is a critical issue to elongate the life of the batteries equipped in sensors. LEACH(Low Energy Adaptive Clustering Hierarchy) is one of the mostly used routing algorithms which reduce the amount of transmitted data and save the energy in the network. In this paper, a new technique to select channels in routing algorithms is suggested and compared with the LEACH, ALEACH and PEGASIS. This technique forms clusters depending upon the node density as the deployement of the nodes is random. As a result, the proposed algorithm presents the better performance of the energy efficiency than those of the current algorithms.

• Journal of the Korean Physical Society
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• v.73 no.12
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• pp.1867-1872
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• 2018

This study proposes a route for surface modification for p-type cobalt oxide-based gas sensors. We deposit a thin layer of Ni on the Co oxide film by sputtering process and annealed at $350^{\circ}C$ for 15 min in air, which changes a typical sputtered film surface into one interlaced with a high density of hemispherical nanoparticles. Our in-depth materials characterization using transmission electron microscopy discloses that the microstructure evolution is the result of an extensive inter-diffusion of Co and Ni, and that the nanoparticles are nickel oxide dissolving some Co. Sensor performance measurement unfolds that the surface modification results in a significant sensitivity enhancement, nearly 200% increase for toluene (at $250^{\circ}C$) and CO (at $200^{\circ}C$) gases in comparison with the undoped samples.

• Journal of the Korean Geotechnical Society
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• v.34 no.9
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• pp.19-32
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• 2018

In this study, the applicability and practicality of landslides monitoring by using wireless sensor network (WSN) was analysed. WSN system consists of a sensor node for collecting and transmitting data using IEEE 802.14e standard, a gateway for collecting data and transmitting the data to the monitoring server. In the topology of the sensor network, a highly flexible and reliable mesh type was adopted, and three testbeds were chosen in each location of Seoul metropolitan area. Soil moisture sensors, tensiometers, inclinometers, and a rain gauge were installed at each testbed and sensor node to monitor the landslide. For the estimation of the optimal network topology between sensor nodes, the susceptibility assessment of landslides, forest density and viewshed analysis of terrain were conducted. As a result, the network connection works quite well and measured value of the volumetric water content and matric suction simulates well the general trend of the soil water characteristic curve by the laboratory test. As such, it is noted that WSN system, which is the reliable technique, can be applied to the landslide monitoring.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.68-77
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• 2010

Wireless sensor networks are installed in various environments and collect sensing data through wireless links. The quality of a wireless link may be unstable due to environment causes and hardware performance in wireless sensor networks. Since the change of the link quality may cause data loss, sensor nodes need to adaptively estimate the change of the link quality. Also, the routing protocol should deal with this situation. In this paper, the adaptive link quality estimation and routing scheme in the large-scale wireless sensor networks are proposed. When the quality of a link is unstable, sensor nodes agilely estimate the quality of links, and the new route is selected. When quality of a link is stable, the link quality is occasionally estimated so that the energy consumption is reduced. Moreover, sensor nodes exchange less beacons in order to reduce an overhead in dense networks. In the case of sparse network, the sensor nodes exchange more beacons for finding a better route. We prove that the proposed scheme can improve the energy efficiency and reliability.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.135-138
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• 2004

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride­trifluoroethylene) (P(VDF-TrFE)) copolymer have been used as a sensor. The advantages of polymer sensor are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. Polymer sensor can be directly embedded in a structure. In this study, nondestructive damage sensitivity of single basalt fiber/epoxy composites was investigated with sensor type and thermal damage using AE and oscilloscope. And AE waveform for epoxy matrix with various damage types was compared to each other. The damage sensitivity of two polymer sensors was rather lower than that of PZT sensor. The damage sensitivity of PVDF sensor did not decrease until thermal damage temperature at $80^{\circ}C$ and they decreased significantly at $110^{\circ}C$ However, the damage sensitivity of P(VDF-TrFE) sensor at $110^{\circ}C$ was almost same in no damage sensor. For both top and side impacts, the difference in arrival time increased with increasing internal and surface damage density of epoxy matrix.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.34-36
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• 2003

In boreal conifers in China's Northeast area, maximum latewood density (MXD) of tree-ring varies in response to growing season temperature. Forest net productivity can be estimated using the Normalized-difference Vegetation Index (NDVI) calculated from satellite sensor data. MXD from the Mohe site in this area was compared with estimates of NPP for 1982-1999 produced by the NDVI model, which was established based on the relationship of leaf area index (LAI) and NDVI. The result shows that the MXD series correlated significantly with the NDVI model estimates series, suggesting that MXD appeared to be an appropriate index for productivity or canopy growth in region where forest productivity is strongly temperature-related.