• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.207-216
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• 1999

A phased array is a multi-element piezoelectric device whose elements are individually excited by electric pulses at programmed delay time. One of the advantages of using phased array in nondestructive evaluation (NDE) application over conventional ultrasonic transducers is their great maneuverability of ultrasonic beam. There are some parameters such as the number and the size of the piezoelectric elements and the inter-element spacing of the elements to design phased array transducer. In this study, the characteristic of ultrasonic beam for phased array transducer due to the variation of the number of elements has been simulated for ultrasonic SH-wave on the basis of Huygen's principle. Ultrasonic beam directivity and focusing due to the change of time delay of each element were discussed due to the change of the number of piezoelectric elements. It was found that ultrasonic beam was much more spreaded and hence its sound pressure was decreased as steering angle of ultrasonic beam was increased. In addition, the ability of ultrasonic bean focusing decreased gradually with the increase of focal length at the same piezoelectric elements. However, the ability of beam focusing was improved as the number of consisting elements was increased.

• Korean Journal of Comparative Education
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• v.22 no.4
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• pp.75-98
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• 2012

This study aims to investigate and compare with each other the global scholarship policy of Korea, China, and Japan, which is supported by government, and to suggest the improvement plan of the Global Korea Scholarship(GKS) program in Korea. Based on the results of comparison study with Chinese and Japanese policies, the implications for GKS program are as follows. First, GKS program needs to be redesigned according to the boundaries of in-bound and out-bound countries. Especially, the GKS program for 'neighboring countries' focusing on East Asian countries, could be developed as the Union of East Asian Nations. Second, to maximize the performance of GKS, the government needs to cooperate more actively and systematically among related departments through all the steps as a national foreign policy, that is, from establishing goals to evaluating performance. Third, the perspectives on GKS must be expanded, not just as a kind of scholarship, but as a policy for developing Korean culture and language. Fourth, out-bound GKS programs must be greatly expanded in relation to short-term programs as well as the quality of in-bound GKS programs. Finally, out-bound GKS programs for the Asian developing countries need to be redesigned and operated under the focus of ODA, to support the invited Parties beyond the foreign resource policy.

• Convergence Security Journal
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• v.18 no.5_2
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• pp.3-10
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• 2018

The drone is an unmanned aircraft that can be steered and controlled using radio waves on the ground, and the pilot moves unmanned without boarding. The history of the unmanned airplane began with military use, and the first unmanned aerial flight was the first successful flight of the 'Sperry Aerial Torpedo' drones built in the United States in 1917 with a bomb. With the development of unmanned aerial technology, the use of military drones has expanded to a wider field. Recently, the use of drones has been utilized in various fields such as agriculture, industry, logistics, broadcasting, and safety, and the scale of the market is also expanding. Although the drones are becoming indispensable to penetrate our lives, they can be used for bad purposes depending on the intended use of the user, but the risk factors are overlooked. Therefore, technical defects related to drones and accidents caused by operator's mistakes can not be completely prevented. However, privacy infringement, security leakage, and terrorism, which may be caused by illegal use of drones, It will not be inhibited and will accelerate.

• Journal of Convergence for Information Technology
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• v.8 no.6
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• pp.243-249
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• 2018

In this paper, we analyzed the effect of modulation scheme and modulation scheme on the dimming level of visible light communication system and studied the effect of distortion due to delayed signal. Currently, the modulation schemes most commonly used in visible light communication result in increasing the communication performance but reducing the brightness of the entire illumination. Continuous Burst Zero Duration will severely degrade lighting. This degrades not only the illumination but also the performance of the whole system and causes Flicker phenomenon. In this paper, we analyze the relationship between modulation technique and illumination - communication performance and investigate the effect of signal delay on visible light communication system. Through simulation, we analyze the performance of IPI-OOK which has the best communication-lighting performance and propose future research directions accordingly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.195-201
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• 2019

The effectiveness of the phased array antenna in wireless power transfer systems is due to its ability to form a beam pattern towards the desired direction. To maximize the efficiency of wireless power transfer through beamforming, the transmitter must recognize the information on the optimal transmission path. To achieve this, the transmitter usually transmits pilot signals periodically and the receiver extracts the optimal beamforming weights using the pilot signals. The receiver then feeds the beamforming weights back to the transmitter. In general, the amount of feedback increases with the number of antennas, which causes feedback overhead when there is a large number of antennas. In this paper, we propose a feedback simplification scheme based on the far-field approximation method. The simulation results are provided to validate the impact of the simplified feedback on the beam pattern.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.8
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• pp.599-606
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• 2019

The pulse gun device is designed to identify the transverse pressure wave propagation/damping mechanism into the combustion flow field and in the combustion chamber according to the arrangement of multiple injectors. The manufactured pulse gun was tested to verify operability at the target combustion pressure and control of the pressure wave intensity. Gas nitrogen was used to pressurize the high-pressure tube and an OHP film of $100{\mu}m$ thickness was used for the diaphragm. To check the speed and intensity of the pressure waves, the dynamic and static pressure were measured using the pressure transducer. The performance test confirmed that the manufactured pulse gun can generate pressure waves with transverse characteristics that can be controled for strength depending on the supply pressure.

• Journal of the Society of Disaster Information
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• v.15 no.1
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• pp.49-66
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• 2019

Purpose: This study aims to apply the counter terrorism policy in pertain to malicious drone abuse and the croweded public places in South Korea. And, to improve counter terrorism protection measure, this study suggests an adoptation of Anti UAV technology into counter terrorism related regulation. Method: Compared to nations' operations of counter terrorism prevention and protection activities with the South Korean gov, problems and limitations are suggested. Results: Anti UAV technology could not be applied for Multi-user facilities by any law due to the limitation, so that it is required to amend counte terrporism related policies and law. Conclusion: This study intends to identify various protection methods against UAV threats. To reduce the risk of UAV, the law of public safety and counter terrorism should be promoted and reinforced for the first.

• Journal of the Korean Society of Mineral and Energy Resources Engineers
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• v.55 no.6
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• pp.604-613
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• 2018

In this study, we analyzed the variations in the received signal strength index (RSSI) measured from Bluetooth beacons based on the strength and propagation direction of Bluetooth low energy (BLE) signal. Using a smartphone, we performed field experiments to investigate RSSI variations in the BLE signal transmitted by non-directional and directional beacons in an amethyst mine. In case of non-directional beacons, as the distance between the Bluetooth beacon and smartphone decreased, the RSSI increases, whereas as the BLE signal strength increased, the RSSI average gradually increased. The mean value of RSSI measured from the directional beacons was changed without relation to the facing angle between the Bluetooth beacon and smartphone. The results of this study can be used as basic data for developing a Bluetooth beacon-based proximity warning system for underground mines.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.786-791
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• 2021

In this paper, in order to minimize limitations such as signal interference and positioning errors in existing indoor positioning systems, a smart LED-based positioning system for excellent line-of-sight radio environments and precise location tracking is proposed to improve accuracy. An IEEE 802.4 Zigbee module is mounted on the SMPS board of a smart LED; RSSI and LQI signals are received from a moving tag, and the system is configured to transmit the measured data to the positioning server through a gateway. For the experiment, the necessary hardware, such as the gateway and the smart LED module, were separately designed, and the experiment was conducted after configuring the system in an external field office. The positioning error was within 70cm as a result of performing complex calculations in the positioning server after transmitting a vector value of the moving object obtained from the direction sensor, together with a signal from the moving object received by the smart LED. The result is a significantly improved positioning error, compared to an existing short-range wireless communications-based system, and shows the level at which commercial products can be implemented.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.178-186
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• 2021

COVID-19 occurred in China in December 2019 and spread to the world. Untact culture becoming commonplace due to the spread of COVID-19, is accelerating digital transformation across society. The government is increasing government fund to overcome national crisis situations such as COVID-19. In order to efficiently execute these government funds, the government and policy financial institutions need to come up with two measures. One is to establish a transparent government fund execution process, and the other is to secure the objectivity of the review process. In this paper, to solve this problem, we designed the execution process of government funds from the government to end users with Consortium Blockchain, and designed a machine learning algorithm for internal review of policy financial institutions. The research data proposed in this paper will be helpful in setting the future government policy direction for government fund execution.