• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1013-1022
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• 2012

Tag collection is one of the major concerns in radio frequency identification(RFID) system. All tags in RFID reader's transmission range send response message back to the reader in response to collection request message on the given rf channel. When multiple tags respond simultaneously, tag-collision may occur. Tag-collision problem is one of the most important issues in active RFID performance. To mitigate this problem, frame slotted ALOHA(FSA) anti-collision protocol is widely used in active RFID system. Several studies show that the maximum system efficiency of FSA anti-collision protocol is 36.8%. In this paper, we propose an efficient slotted CSMA/CA protocol to improve tag collection performance. We compare our protocol to the FSA anti-collision protocol. For the experiment, an 433MHz active RFID system is implemented, which is composed of an RFID reader and multiple tags. We evaluated the tag collection performance using one RFID reader and 40 tags in the real test bed. The experimental result shows that proposed protocol improves the tag collection time, round and collision probability by 18%, 37.4% and 77.8%, respectively.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.3
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• pp.181-188
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• 2003

In this paper, we introduce a magnetic noise shielding method to reduce the noise effects in permanent magnet based MRI systems. Through FEM electromagnetic analyses, we have shown that the magnetic noise component parallel to the main magnetic field is the major component that makes various artifacts in the images obtained with a permanent magnet based MRI. Based on the FEM analyses, we have developed an active magnetic noise shielding system composed of a magnetic field sensor, compensation coils, and a coil driving system. The shielding system has shown a noise rejection ratio of about 30dB at the frequency below several Hz. We have experimentally verified that the shielding system greatly improves the image quality in a 0.3 Tesla MRI system.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.05a
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• pp.640-643
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• 2008

현재 우리나라는 좁은 국토와 도시 집중화로 인해 급증하고 있는 지하매설물의 체계적인 관리가 어느 때보다 요구되고 있다. 그러나 다른 분야에서 빠르게 진행되고 있는 전산화 및 정보화 작업에 비해 상대적으로 더딘 지리정보체계 구축으로 지하매설물 관리를 위한 정보시스템이 미비한 상태이다. 이는 지리정보체계 구축 방법에 어려움과 소요되는 인력, 비용, 시간 등이 크기 때문으로 판단된다. 본 논문에서는 GPS와 능동형 RFID를 이용한 위치기반 지하매설물 정보시스템의 구현을 기술하고 시뮬레이션하였다. 이 시스템은 GPS NMEA Sentence의 위치정보와 능동형 RFID의 인식정보를 결합한 데이터를 이용하여 정확하고 체계적인 지하매설물 정보 구축이 가능하고, 효율적인 지하매설물 관리를 위한 인터페이스를 제공한다.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.154-156
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• 2008

본 연구에서는 종전의 전압형 및 전류형 능동전력필터를 대체 할 수 있으며, 부하의 특성에 무관하게 적용 가능한 Z-소스 인버터(Z-source inverter) 토폴로지의 능동전력필터에 대하여 고찰하였다. Z-소스 토폴로지의 능동전력필터의 보상 직류전원으로는 연료전지 PEMFC를 사용하였다. 본 연구에서 제안된 시스템은 고조파 발생원 비선형 부하와 병렬로 연결된 Z-소스 능동전력필터와 7고조파 (420Hz) 동조 필터로 구성되며 Z-소스 능동전력필터의 스위치 스트레스를 감소할 수 있다. 제안된 Z-소스 하이브리드 능동전력필터(Z-HAF : Z-source hybrid active power filter)의 보상 알고리즘으로는 전류 동기 검출법(CSD)을 사용하였으며, PSIM 시뮬레이션에 의하여 제안된 Z-HAF의 정상상태에서의 보상 성능을 파악하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.915-921
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• 2017

Recently, studies to reduce vibration and noise of automobiles have been actively conducted. However, previous studies did not concentrate on the optimization of the mount system with passive or active mounts. This study analytically studies an active mounting system with three active structural paths between source and receiver and the feasibility has been verified. Active mounting system has a coupled structure of piezoelectric stack actuators and passive mounts. A dynamic model of the whole system is prepared and the control force and phase of the stack actuators in each path are determined to target full isolation of each path. Its performance on vibration attenuation is investigated and based on it, optimized combinations of passive and active paths for the best attenuation are presented.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.1
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• pp.42-48
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• 2011

This paper presents the vibration reduction algorithm at the walking-will recognition sensors on the uneven terrain. Recently, concern about walking assistant aids is increasing according to the increase in population of elder and handicapped person. However, most of walking aids don't have any actuators for its movement. So, general walking aids have weakness for its movement to upward/download direction of slope. To overcome the weakness of the general walking aids, many researches for active type walking aids are being progressed. Especially, vibration analysis and impulse reduction are one of the important elements of the active-type walking aid during moving on the outdoor area because the ground has many kinds of obstacles such as speed dumps, puddles and so on. So, we analyze the influence from vibration by uneven terrain. And then, we propose the impulse reduction algorithm to overcome the vibration. All the processes are verified experimentally in an active-type walking aid.

• Review of KIISC
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• v.13 no.4
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• pp.49-59
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• 2003

정보보호기술이 '수동형'에서 점차로 '능동형'으로 진화하고 있는 가운데, Secure OS가 능동형 정보보호기술의 핵심으로 주목받고 있다. Secure OS는 서버시스템 보안의 원천적 기술로 접근통제에 관한 보안정책, 보안모델 및 보안메커니즘에 대하여 검증 가능한 방법으로 안전ㆍ신뢰성이 확보되어야 한다. 이에 본 논문에서는 Secure OS 핵심기술의 이해와 더불어 Secure OS 개발 시 안전ㆍ신뢰성을 확보하기 위하여 이론적으로 잘 정립되고 정형화된 보안정책, 보안모델 및 보안메커니즘에 대하여 살펴본다.

• Proceedings of the Korea Multimedia Society Conference
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• 2004.05a
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• pp.495-498
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• 2004

기존의 정보보호 방식은 시스템 설계 단계부터 반영된 것이 아니기 때문에 서비스 제공 이후에 발생 가능한 다양한 취약점 공격에 대한 효과적인 대응에 태생적 한계를 지니고 있다. 따라서 사이버 공격에 대한 기존의 수동적인 대응에서 벗어나 능동적이고 공격적인 대응을 할 수 있는 기술들이 필요하게 되었다. 본 논문에서는 우선 기존의 망에 적용한 역추적 시스템을 분석한 다음, 정보통신망 자체를 사이버 공격으로부터 보호하며, 정보통신망의 보안 취약점을 없애 해킹이나 정보유출을 원천적으로 차단할 수 있는 능동형 보안 관리 기술인 역추적 시스템을 분석하여 액티브 네트워크 기반의 역추적 시스템을 분석하였다.

• The Journal of the Korea Contents Association
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• v.15 no.7
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• pp.591-600
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• 2015

Recently high interest in health and fitness has led to vibrant researches for the active fitness system to learn and enjoy the exercise program for oneself. In this paper, we design and implement the active spinning training system which enables user to have self-learning and experience of customized spinning training program by the biometric and movement information acquired from user's physiological signals. The proposed system provides the appropriate difficulty of spinning program which reflects the concordance rate of spinning dance gestures and the amount of exercising by analyzing the physical status of participant from his brain and pulse waves and recognizing the skeletal movement in real time. For the higher exercise effect, the system offers a virtual personal trainer to show the correct poses and controls the level of difficulty depending on the concordance rate of participant's motions. The experiment with various participants through the proposed system shows that it is able to help users in getting the available exercise effect in comparatively short time.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.1-9
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• 2013

An active anti-ship missile decoy system was designed conceptually to analyze propulsion system requirements and feasibility to use a liquid bi-propellant rocket engine. Overall mass, size, and shape were assumed referring to specifications of Nulka which was developed by US and Australia in 1990s. The propulsion system was assumed to be a 1,000 N-class $H_2O_2$/kerosene rocket engine with a pressurized feed system. A three-degree-of-freedom optimal trajectory was calculated based on the assumptions, and mass budget was designed from the calculation results. It was found that the requirements for the propulsion system is that it shall be operated more than 100 sec; it shall be re-ignitable; it shall have a throttle capability of a range from 35% to 100% when the maximum thrust at sea level is 1,000 N.