• Journal of Sensor Science and Technology
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• v.29 no.3
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• pp.201-204
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• 2020

In this study, we fabricated and evaluated graphene composite based 3D scaffolds and planar films. The hybrid composite was prepared by mixing a calculated amount of graphene nanopowder and polydimethylsiloxane in tetrahydrofuran solution. The hybrid composite is easy to manufacture into various forms using direct printing technology or a pressing method. A 3D scaffold structure was prepared at ambient temperature with a flow rate of 240 mm/min. The nozzle pressure was maintained at 350 kPa by adjusting the viscosity of the composite material. The planar film was prepared at different thicknesses using a roll-to-roll equipment. The prepared hybrid nanocomposites were evaluated to investigate their electrical properties according to temperature and mechanical deformation. The obtained results were consistent with each other. Therefore, it can be used effectively as sensors through shape definition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.833-839
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• 2013

In this study, an experiment was performed to monitor the two-dimensional shape of a cantilever composite structure using fiber Bragg grating (FBG) sensors. To monitor the shape of a composite structure, a deflection equation developed by NASA was applied and a composite beam attached to three FBG sensors was used. In the experiment, the shape of the composite beam was successfully estimated and an error was evaluated by comparing a real deflection. The error increased with real deflection; therefore, it was compensated by using the linear relationship between the error and the real deflection. After compensating the error, the measured deflection shows good agreement with the real deflection. Finally, the experiment shows that the FBG sensor and the deflection equation are suitable for monitoring the deflection curve of the beam structure with compensation of the error.

• Smart Structures and Systems
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• v.8 no.3
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• pp.303-320
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• 2011

Comparing to active damage monitoring, impact localization on composite by using time reversal focusing method has several difficulties. First, the transfer function of the actuator-sensor path is difficult to be obtained because of the limitation that no impact experiment is permitted to perform on the real structure and the difficulty to model it because the performance of real aircraft composite is much more complicated comparing to metal structure. Second, the position of impact is unknown and can not be controlled as the excitation signal used in the active monitoring. This makes it not applicable to compare the difference between the excitation and the focused signal. Another difficulty is that impact signal is frequency broadband, giving rise to the difficulty to process virtual synthesis because of the highly dispersion nature of frequency broadband Lamb wave in plate-like structure. Aiming at developing a practical method for on-line localization of impact on aircraft composite structure which can take advantage of time reversal focusing and does not rely on the transfer function, a PZT sensor array based phase synthesis time reversal impact imaging method is proposed. The complex Shannon wavelet transform is presented to extract the frequency narrow-band signals from the impact responded signals of PZT sensors. A phase synthesis process of the frequency narrow-band signals is implemented to search the time reversal focusing position on the structure which represents the impact position. Evaluation experiments on a carbon fiber composite structure show that the proposed method realizes the impact imaging and localization with an error less than 1.5 cm. Discussion of the influence of velocity errors and measurement noise is also given in detail.

• Bulletin of the Korean Chemical Society
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• v.27 no.1
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• pp.65-70
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• 2006

An amperometric glucose biosensor has been developed based on the use of the nanoporous composite film of sol-gel-derived zirconia and perfluorosulfonated ionomer, Nafion, for the encapsulation of glucose oxidase (GOx) on a platinized glassy carbon electrode. Zirconium isopropoxide (ZrOPr) was used as a sol-gel precursor for the preparation of zirconia/Nafion composite film and the performance of the resulting glucose biosensor was tuned by controlling the water content in the acid-catalyzed hydrolysis of sol-gel stock solution. The presence of Nafion polymer in the sol-gel-derived zirconia in the biosensor resulted in faster response time and higher sensitivity compared to those obtained at the pure zirconia- and pure Nafion-based biosensors. Because of the nanoporous nature of the composite film, the glucose biosensor based on the zirconia/Nafion composite film can reach 95% of steady-state current less than 5 s. In addition, the biosensor responds to glucose linearly in the range of 0.03-15.08 mM with a sensitivity of 3.40 $\mu$A/mM and the detection limit of 0.037 mM (S/N = 3). Moreover, the biosensor exhibited good sensor-to-sensor reproducibility (~5%) and long-term stability (90% of its original activity retained after 4 weeks) when stored in 50 mM phosphate buffer at pH 7 at 4 ${^{\circ}C}$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.05a
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• pp.39-40
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• 2012

Construction IT convergency proposes advanced management abilities of a construction project. Sensing data provided by various sensor technologies can be utilized for diverse management areas. This study analyzes required functions of sensors for implementing time, cost, safety and quality management, focusing on the ground works including excavation, pipe installation, retaining wall etc. Therefore, this study first generates essential management areas, analyzes cutting-edge sensor technologies appropriated for the areas, and finally proposes a matrix system that represents relationships between the management areas and sensor technologies, The proposed system is expected to reinforce construction management abilities by integrating sensor technologies.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.7
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• pp.324-325
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• 2001

In this study, the characteristics of ultrasonic sensor fabricated with PZT-Polymer 1-3 type composites are investigated. The 3-D Underwater object recognition using the self-made ultrasonic sensor and SOFM neural network is presented. The ultrasonic sensor is satisfied with the required condition of commercial ultrasonic sensor in underwater. The 3-D underwater object recognition for the training data and the testing data are 100[100%], respectively. The experimental results have shown that the ultrasonic sensor fabricated with PZT-Polymer 1-3 type composites can be applied for sonar system.

• Composites Research
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• v.32 no.5
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• pp.237-242
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• 2019

In this research, a capacitive pressure sensor (Piezocapacitive Sensor) was fabricated using carbon black powder containing poly-dimethylsiloxane (PDMS) with micro-grid patterned surface. To investigate the effect of carbon black powder and micro-grid pattern on the sensor's performance, various sensors were fabricated with different carbon black powder concentration and grid pattern density. The performances of the developed sensors were compared in terms of operating range and sensitivity.

• Composites Research
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• v.29 no.1
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• pp.1-6
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• 2016

Low-speed impact was localized on a stiffened composite structure, using 4 FBG sensors with 100 kHz-sampling rate interrogator and devised localization algorithm. The composite specimen consists of a main spar and several stringers, and the overall size of the specimen's surface is about $0.8{\times}1.2m$. Pre-stored reference data for 247 grid locations and 36 stiffener locations are gathered and used as comparison target for a random impact signal. The proposed algorithm uses the normalized cross-correlation method to compare the similarities of the two signals; the correlation results for each sensor's signal are multiplied by others, enabling mutual compensation. 20 verification points were successfully localized with a maximum error of 43.4 mm and an average error of 17.0 mm. For the same experimental setup, the performance of the proposed method is evaluated by reducing the number of sensors. It is revealed that the mutual compensation between the sensors is most effective in the case of a two sensor combination. For the sensor combination of FBG #1 and #2, the maximum localization error was 42.5 mm, with average error of 17.4 mm.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• Journal of KIISE:Information Networking
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• v.33 no.2
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• pp.131-138
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• 2006

To achieve security in wireless sensor networks(WSN), it is important to be able to encrypt and authenticate messages sent among sensor nodes. Due to resource constraints, many key agreement schemes used in general networks such as Diffie-Hellman and public-key based schemes are not suitable for wireless sensor networks. The current pre-distribution of secret keys uses q-composite random key and it randomly allocates keys. But there exists high probability not to be public-key among sensor nodes and it is not efficient to find public-key because of the problem for time and energy consumption. To remove problems in pre-distribution of secret keys, we propose a new cryptographic key management protocol, which is based on the clustering scheme but does not depend on probabilistic key. The protocol can increase efficiency to manage keys because, before distributing keys in bootstrap, using public-key shared among nodes can remove processes to send or to receive key among sensors. Also, to find outcompromised nodes safely on network, it selves safety problem by applying a function of lightweight attack-detection mechanism.