• 산업기술연구
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• 제29권B호
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• pp.145-149
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• 2009

A RF-DC converter is one of the most important components for a wireless power transmission. It has been developed for many applications such as space solar power system, and Radio Frequency Identification(RFID). In this paper, we designed three types of RF-DC converter and compare the performance of each. All types RF-DC convertoer have a maximum conversion efficiency at input power level of 0 dBm~5 dBm and RF-DC converter of third type was the best performance that has a 21.9% of conversion efficiency.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.82-91
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• 2004

This article deals with a minimum energy control law of S-CVT connected to a dc motor. The S-CVT can smoothly transit between the forward, neutral, and reverse states without any brakes or clutches, and its compact and simple design and its relatively simple control make it particularly effective for mechanical systems in which excessively large torques are not required. And such an S-CVT equipped power transmission has the advantage of being able to operate the power sources in their regions of maximum efficiency, thereby improving the energy efficiency of the transmission system. The S-CVT was intended to primarily for use in small power capacity transmissions, thus a dc motor was considered here as the power source. We first review the structure and operating principles of the S-CVT, including experimental results of its performance. And then we describe a minimum energy control law of S-CVT connected to a do motor. To do this, we describe the results of an analysis of the dynamics of an S-CVT equipped power transmission and the power efficiency of a DC motor. The minimum energy control design is carried out via B-spline parameterization. And we show numerical results obtained from simulations illustrate the validity of our minimum energy control design, benchmarked with a computed torque control algorithm for S-CVT.

• 한국통신학회논문지
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• 제38A권7호
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• pp.571-579
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• 2013

본 논문은 셀룰러 네트워크에서 D2D (device-to-device) 통신을 고려한 시스템의 에너지 효율적인 모드 선택 기법 (mode selection) 및 파워 할당 기법 (power allocation)을 제안한다. 본 논문에서는 각 단말(device)의 에너지 효율성의 합 측면에서 에너지 효율성 (energy efficiency)을 분석한다. 먼저, 각 단말의 모든 가능한 모드에 대해 에너지 효율을 최대화하는 전송 파워를 계산한다. 제안하는 파워 할당 기법은 시스템 용량 측면에서 최적은 아니지만, 에너지 효율성 측면에서 최적의 성능을 보인다. 제안하는 전송 파워 할당 기법을 기반으로, 모든 가능한 모드에 대해 에너지 효율성을 구한다. 다음 단계로, 모든 가능한 모드 중에서 최대의 에너지 효율성을 갖는 모드를 구하며 동시에 해당 모드의 할당 전송 파워를 도출할 수 있다. 제안 기법은 에너지 효율성 측면에서 최적의 성능을 보이며, 기존 기법에 비해 월등한 성능을 보인다.

• 한국기계가공학회지
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• 제17권5호
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• pp.30-36
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• 2018

Automotive fuel efficiency regulations and air pollution control are hot issues of recent years in the automotive industry. To solve these regulation problems, many studies are continuing to improve the transmission efficiency of transmissions. Tapered roller bearings are useful to improve the transmission efficiency in the recent automobile parts. The frictional losses in the tapered roller bearings are mainly composed of the rolling friction and the sliding friction, and are dependent upon the load, the lubrication, the rotation speed of bearings, and etc. In this paper, the operating conditions of the transmission are defined and then the power losses of each bearing are calculated. In addition, improvement options are suggested after identifying the design factors influenced much by the improvement effect of power loss under the operating conditions of each bearing. We compare the power losses of the entire transmission system due to bearing improvements by comparing the friction losses between the original design and the improved design. Lastly, it is shown that the calculated power losses are valid by comparing the test values and the theoretical values for the frictional torque characteristics of the original and improved bearings.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권9호
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• pp.383-387
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• 2003

In this paper, we have studied about optimal transmission efficiency characteristics of pulse energy in a coal plant for removing environmental polluted gas. The electrical efficiency of pulse power systems depends on impedance of the reactor. To obtain high efficiency, we used MPC(Magnetic pulse compressor) as the power switch and tested their characteristics as electrode length of the reactor and charging voltage of capacitor, As results, we obtained a compressed pulse such as pulse voltage of 10㎸, rising time 200ns and pulse width of 500ns. With increasing electrode length, the load impedance was decreased but the electrical efficiency was increased.

• 전기학회논문지
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• 제62권3호
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• pp.349-354
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• 2013

Wireless power transmission introduced by Tesla has instrumented by many scientists of the world. This technique first was utilized as wireless communications such as radio in long range transmission. And contactless transmission using inductive property was used on white goods. In 2007, MIT' lab introduced that new wireless power transmission by magnetic resonance which has about 50% efficiency and 2M transmission distances, it was a chance to refocus a new possibility of wireless power transmission. In this paper, using LC coupling compensate the short distances of contactless transmission, this simple method could transmit about 30cm distances. Using this approach, it can be solved the short transmission distances, a drawback of Electromagnetic inductive coupling method.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제5권4호
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• pp.87-94
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• 2016

제안된 논문은 기지국의 에너지 효율을 최대화하기 위한 에너지 전송 방식에 관한 것으로, 기존의 데이터 처리량과 송신전력 사이의 지수 함수적 관계에 따른 비효율적 문제를 해결함으로써 서비스의 유형에 따른 데이터를 분류하고, 무선 네트워크 환경의 기지국에서 사용자 들에게 전송 되는 최적의 데이터 량에 따른 에너지 최적화 지점을 찾아내는 방법이다. 이를 위해, 기지국에서 사용자에게 전송되는 데이터의 양 및 유지시간을 조절하여 데이터 전송의 에너지 효율 최적화 지점을 찾을 수 있는 EETA 알고리즘(Energy-Efficient Transmission Algorithm)을 제안한다. 결과적으로 제안한 방식은 기존 기지국 대비 에너지 효율이 약 10% 향상됨을 알 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권12호
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• pp.5898-5916
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• 2018

In this paper, the downlink performance of multi-cell distributed antenna systems (DAS) with a single user in each cell is investigated. Assuming the channel state information is available at the transmitter, four transmission modes are formulated as combinations of remote antenna units (RAUs) selection and cooperative transmission, namely, non-cooperative transmission without RAU selection (NCT), cooperative transmission without RAU selection (CT), non-cooperative transmission with RAU selection (NCT_RAUS), and cooperative transmission with RAU selection (CT_RAUS). By using probability theory, the cumulative distribution function (CDF) of a user's signal to interference plus noise ratio (SINR) and the system ergodic capacity under the above four modes are determined, and their closed-form expressions are obtained. Furthermore, the system energy efficiency (EE) is studied by introducing a realistic power consumption model of DAS. An expression for determining EE is formulated, and the closed-form tradeoff relationship between spectral efficiency (SE) and EE is derived as well. Simulation results demonstrate their consistency with the theoretical analysis and reveal the factors constraining system EE, which provide a scientific basis for future design and optimization of DAS.

• 대한조선학회논문집
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• 제50권3호
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• pp.153-159
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• 2013

The power transmission system has always been considered critical for a human powered boat(or water bike) since it first showed up at Human Powered Vessel Festival. Mechanical problems, such as abrasions and other damages of the gear system for the power transmission, lead to poor durability and low efficiency of a boat. This paper described mechanical problems and a design process of power transmission system and then suggested the method to solve the problems. It is selected a module and a type of gears that are structurally stable thus can transmit the power durable. Especially the lower gear box is applied to CRP(contra rotating propeller) system for improving the structural stability and the propeller efficiency as well. As the results, the upper and lower gear box are designed and manufactured. And from the trial test, it is confirmed that the power transmission system is reliable.

• 반도체디스플레이기술학회지
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• 제20권4호
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• pp.102-107
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• 2021

In this paper, the measurements of received power was shown and compared in two developed 5.8GHz 25W wireless charging systems. One is the system using commercial transmission antenna, and the other is the system using transmission antenna combined with metamaterial. The system combined with metamaterial shows higher received power due to negative reflective index of metamaterial. In addition, a comparative analysis of the systems shows that the transmission efficiency in the systems can decrease the real gain of transmission antenna due to higher side robe of beam pattern. The side robe beams of transmitting antenna interferes transmitted beam with the reflected beams from the bottom region due to the side robes. The failure problems of the RF wireless charging systems are discussed and proposed in order to charge mobile devices through the RF wireless charging system.