• Tribology and Lubricants
• /
• 제25권4호
• /
• pp.225-230
• /
• 2009

Seals are very useful machine components in protection of leakage of lubricant or working fluid, and incoming of debris from outside. Various elastomer are widely used as sealing materials and the shaft surfaces are generally coated with high hardness material after heat treatment. It is generally known that the foreign debris and wear particles get stuck into sealing surface, the steel shaft surface can be damaged and worn by mainly abrasive wear. In this paper, using MARC, contact analysis are conducted to show the hard coated steel shaft surface can be fatigue failed by very small elastic particle intervened between seal and steel surface. Variations of contact and von-Mises stress distributions and contact half-widths with interference and coating thickness are presented. The maximum von-Mises stress occurs always in the coating layer or between coated layer/substrate interface. Therefore the coated sealing surface can be fatigued and then failed by very small particles. The results can be used in design of sealing surface and further studies are required.

• Tribology and Lubricants
• /
• 제29권3호
• /
• pp.180-185
• /
• 2013

The purpose of this study was to analyze the tribological characteristics of the Electronic control suspension System in a car. In the first example, the cilp used to attach the front electronic control suspension(ECS) system's control actuator was fastened very tightly. Thus, the wire was cut because of continual rotation of the shock-up shover piston rod used to adjust the height of the car. This verified the disconnection phenomenon where wire damaged makes it impossible for the ECS system to send signal to the actuator. The second example, involved a minute hole that allowed gas to leak from the ECS system. As a result, the height of the car verified the down phenomenon. In the third example, the resistance of a wire measured at $0.21{\Omega}$, when the G sensor was disconnected from the system. This verified the system shutdown and lighting of the ECS warning lamp because of body interference caused by a slight pressure on the battery cover. Therefore, quality control is always necessary to ensure safety and durability of a car.

• ETRI Journal
• /
• 제39권6호
• /
• pp.794-802
• /
• 2017

In this paper, a wireless powered communication network (WPCN) consisting of a hybrid access point (H-AP) and multiple user equipment (UE), all of which operate in full-duplex (FD), is described. We first propose a transceiver structure that enables FD operation of each UE to simultaneously receive energy in the downlink (DL) and transmit information in the uplink (UL). We then provide an energy usage model in the proposed UE transceiver that accounts for the energy leakage from the transmit chain to the receive chain. It is shown that the throughput of an FD WPCN using the proposed FD UE (FD-WPCN-FD) can be maximized by optimal allocation of the UL transmission time to the UE by solving a convex optimization problem. Simulation results reveal that the use of the proposed FD UE efficiently improves the throughput of a WPCN with a practical self-interference cancellation capability at the H-AP. Compared to the WPCN with FD H-AP and half-duplex (HD) UE, FD-WPCN-FD achieved an 18% throughput gain. In addition, the throughput of FD-WPCN-FD was shown to be 25% greater than that of WPCN in which an H-AP and UE operated in HD.

• Journal of Power Electronics
• /
• 제13권1호
• /
• pp.170-176
• /
• 2013

Power converters produce a vast range of harmonics, subharmonics and interharmonics. Harmonics analyzing tools based on the Fast Fourier Transform (FFT) assume that only harmonics are present and the periodicity intervals are fixed, while these periodicity intervals are variable and long in the presence of interharmonics. Using FFT may lead to invalid and undesired results due to the above mentioned issues. They can also lead to problems such as frequency blending, spectral leakage and the picket-fence effect. In this paper, the group-harmonic weighting (GHW) approach has been presented to identify the interharmonics in a power system. Afterwards, a modified GHW has been introduced to calculate the proper bandwidth for analyzing the various values of interharmonics. Modifying this method leads to more precise results in the FFT of a waveform containing inter harmonics especially in power systems with a fundamental frequency drift or frequency interference. Numerical simulations have been performed to prove the efficiency of the presented algorithm in interharmonics detection and to increase the accuracy of the FFT and the GWH methods.

• 한국정보통신설비학회:학술대회논문집
• /
• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
• /
• pp.414-417
• /
• 2008

This paper presents the design and analysis of 2.45GHz Low-IF Mixer using CMOS 0.18um. The Mixer is implemented by using the Gilbert-type configuration, current bleeding technique, and the resonating technique for the tail capacitance. And the design of this Double Balance Mixer is based on its lineaity since it is important in the interference cancellation system. The low flicker noise mixer is implemented by incorporating a double balanced Gilber-type configuration, the RF leakage-less current bleeding technique, and Cp resonating technique. The proposed mixer has a simulated conversion gain of 16dB a simulated IIP3 of -3.3dBm and P1dB is -19dBm. A simulated noise figure of 6.9dB at l0MHz and a flicker corner frequency of 510kHz while consuming only 10.65mW od DC power. The layout of Mixer for one-chip design in a 0.18-um TSMC process has 0.474mm$\times$0.39 mm size.

• 한국정보통신학회논문지
• /
• 제6권5호
• /
• pp.724-730
• /
• 2002

디지털 통신시스템에서는 인접채널에 대한 간섭을 최대한 줄이기 위하여 필연적으로 선형 전력증폭기가 요구된다. 선형 전력증폭기는 매우 다양하며, 그 중에서도 전방제환 전력증폭기는 구조상 광 대역이면서 선형화 정도가 매우 우수하기 때문에 많이 이용된다. 전방궤환 전력증폭기는 지연 선로의 손실로 인하여 전체효율이 감소한다. 본 논문에서는 이러한 지연 선로를 손실이 매우 작은 지연 여파기를 사용함으로써 효율과 선형성을 동시에 개선하였다. 측정 결과, ACLR이 약 17.43(dB) 개선되었으며, 이것은 지연 여파기를 사용함으로써 3.44(dB) 더 개선되었음을 나타낸다.

• 문화기술의 융합
• /
• 제8권5호
• /
• pp.469-475
• /
• 2022

최근의 구조물공사는 건물과 근접하여 대규모, 대심도 지하굴착 공사로 흙막이벽과 버팀보의 설치가 복잡해지고, 구조물 슬래브의 간섭을 피하기 위한 버팀보의 단수가 많아졌다. 이러한 시공공정은 구조물의 시공이음 개소의 증가와 누수 및 벽체균열 증가를 유발하는 요인이 되어 구조물 전체의 내구성과 시공성 저하 및 공사기간의 증대로 이어졌다. 본 연구는 시공이음 개소를 축소하기 위한 방안으로서 버팀보 2단을 동시에 해체하는 것을 계획하고, 이를초기가정토압에 의한 반력 값과 현장의 계측치를 응답비로 가정하여 토압을 보정하였다. 반복시산법을 통해 보정토압을 재 산정한 후, 버팀보 2단 동시해체가 가능함을 수치해석으로 검증하였다. 최종 보정 토압을 적용한 수치해석결과, 설계반력에 대한 계측 값이 최대 197%로 나타났다. 이는 지반에 시행한 그라우팅의 효과와 설계 시 지반 특성치를 다소 과소평가한 데에서 기인된 것으로 분석되었다. 본 연구에서 수행한 응답비를 고려한 보정토압 산정결과를 바탕으로 버팀보 해체공정의 개선이 가능함을 해석적으로 입증하였다. 또한 이를 바탕으로 시공이음 축소로 누수에 의한 균열 감소와 시공성도 개선되어 전체적인 공기의 단축도 가능할 것으로 검토되었다. 그러나 현장마다 지반여건과 가시설 및 보강공법 등의 차이가 있어 이를 적용하기 위해서는 충분한 검토와 확인이 필요할 것으로 판단된다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.115-116
• /
• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• 한국전자거래학회지
• /
• 제18권3호
• /
• pp.107-123
• /
• 2013

무선센서 네트워크 환경에서 센서노드들에 대한 식별자 노출을 억제함으로써 익명성을 보장하고 실시간 인증, 인증의 경량화, 동기화 등이 요구되고 있다. 특히 무선 채널상에서 이루어지는 통신은 제3자에 의한 위치정보가 노출되거나 프라이버시 침해 및 보안상의 취약점이 존재한다. 익명성은 유 무선 네트워크 환경에서 중요한 문제로 폭넓게 연구되어왔다. 센서 노드는 노드간의 무선망 구성을 기본으로 하여 계산능력의 제한과 저장장치의 제한, 전력 장치의 소형화가 강조되고 있다. 본 논문에서는 생체기반의 D. He scheme을 개선하여 네트워크 성능 향상과 익명성을 보장하며 URSC(Unique Random Sequence Code)와 가변식별자(variable identifier)를 이용한 실시간 인증 프로토콜을 제안한다.

• 한국전자파학회논문지
• /
• 제29권6호
• /
• pp.424-432
• /
• 2018

본 논문에서는 현재 산업현장에 많이 쓰이고 있는 개방형 컨베이어 벨트형 마이크로파 건조기의 전자파 차폐 특성에 대해 분석 및 연구를 진행하였다. 특히, 범용의 2.45 GHz 마그네트론을 사용한 개방형 컨베이어 벨트형 건조기의 전자기파 누설 문제를 직사각형 도파관에 요철을 적용하여 개선하였다. 본 논문은 요철을 적용한 직사각형 도파관의 감쇠 특성을 살펴보기 위해 제안된 도파관의 구조에 따른 최적 차폐특성의 모의해석을 수행하였다. 또한, 요철 직사각형 도파관을 제작하여 IEEE Std. 299 규격에 따라 차폐특성을 검증하기 위해 제안된 요철 직사각형 도파관을 갖는 실제 마이크로파 건조기 제품에 적용하였으며, 대략 30 dB 이상의 차폐특성을 확인하였다.