• Journal of Communications and Networks
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• 제18권3호
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• pp.340-350
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• 2016

The performance of large-scale cognitive radio (CR) networks with secondary users sustained by opportunistically harvesting radio-frequency (RF) energy from nearby primary transmissions is investigated. Using an advanced RF energy harvester, a secondary user is assumed to be able to collect ambient primary RF energy as long as it lies inside the harvesting zone of an active primary transmitter (PT). A variable power (VP) transmission mode is proposed, and an energy-based opportunistic spectrum access (OSA) strategy is considered, under which a secondary transmitter (ST) is allowed to transmit only if its harvested energy is larger than a predefined transmission threshold and it is outside the guard zones of all active PTs. The transmission probability of the STs is derived. The outage probabilities and the throughputs of the primary and the secondary networks, respectively, are characterized. Compared with prior work, the throughput can be increased by as much as 29%. The energy-based OSA strategy can be generally applied to a non-CR setup, where distributed power beacons (PBs) are deployed to power coexisting wireless signal transmitters (WSTs) in a wireless powered sensor network.

• Advances in aircraft and spacecraft science
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• 제8권1호
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• pp.17-30
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• 2021

This is an investigation for a more electric regional aircraft, considering the ATR 72 aircraft as an example and the electrification of its four double slotted flaps, which were estimated to require an energy of 540 Wh for takeoff and 1780 Wh for landing, with a maximum power requirement of 35.6 kW during landing. An analysis and evaluation of three energy harvesting systems has been carried out, which led to the recommendation of a combination of a piezoelectric and a thermoelectric harvesting system providing 65% and 17%, respectively, of the required energy for the actuators of the four flaps. The remaining energy may be provided by a solar energy harvesting photovoltaic system, which was calculated to have a maximum capacity of 12.8 kWh at maximum solar irradiance. It was estimated that a supercapacitor of 232 kg could provide the energy storage and power required for the four flaps, which proved to be 59% of the required weight of a lithium iron phosphate (LFP) battery while the supercapacitor also constitutes a safer option.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.631-631
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• 2013

Battery has major drawbacks including its size and life expectancy, and environmental problem. As an alternative, energy harvesting is emerging as a potential solution to replace battery along with more energy-efficient IT devices. The idea of harnessing energy from our living environment is sustainable, semi-permanent, and eco-friendly. Also, unlike battery, energy harvester does not require much space to store energy. Therefore, energy harvesting can provide a better source of power for small, portable, and wireless devices. Among various ways of harvesting energy from our surroundings, triboelectricity is chosen due to its potential to be miniaturized, and efficient. Triboelectric effect occurs as two different materials with different polarity of charge separation come into contact through friction, and then become separated so that electric potential difference is achieved. In this research, such characteristic of triboelectricity is used as a way to convert ambient mechanical energy into electric energy.Series of recent researches have shown promising results that the triboelectric energy harvester can be simple and cost effective. However, sufficient electricity level required to operate mobile devices has not yet been achieved.In this research, our group focuses on the design and optimization of triboelectric energy harvesting device to enhance its output. By using maskless lithography to pattern Kapton film and silicon substrate, which is used as a mold for PDMS thin layer, and sputtering metal electrodes on each side, we fabricate and demonstrate different designs of triboelectric energy harvester that utilizes the contact electrification between a polymer thin film and a metal thin foil. In order to achieve optimized result, the output voltage and current are measured under diverse conditions, which include different surface structure and pattern, material, and the gap between layers.

• 감성과학
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• 제14권3호
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• pp.435-444
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• 2011

유비쿼터스 헬스케어 기술 및 휴대용 전자기기의 발전은 지속적으로 전원을 공급하기 위한 새로운 에너지원을 요구하고 있으며, 이러한 점에서 의류를 통한 인체 에너지 수확 시스템의 연구가 요청되고 있다. 인체에너지를 수확하는 방식의 하나인 열전은 인체와 주위 환경간의 온도차이로부터 에너지를 수확하는 방식으로, 본 연구에서 의복을 통한 열전에너지 수확의 기초자료를 확보하기 위하여 인체표면 온도의 분포를 실증적으로 고찰하였다. 이를 위해 체표 구간을 설정하고 구간별 온도분포를 분석하였다. 분석 결과, 상체의 체표온도가 하체에 비해 높았고 특히 심장과 가깝고 혈류량이 많은 몸통 부위의 체표온도가 높았다. 뒷목과 등, 허리의 후면 부위 체표온도가 앞면에 비해 높았으며, 팔 부위의 경우 위쪽 부위의 체표온도가 아래쪽 부위보다 높고 팔 후면이 정면과 측면에 비해 온도가 낮게 나타났다. 체표 구간별 평균 온도와 환경온 간의 차이값이 가장 높아 열전 수확 기능구조 설치에 가장 적합한 위치는 뒷목 부위로 나타났고, 등과 허리 부위, 측면 어깨부위, 가슴 부위, 정면 위팔 부위, 배 부위가 그 뒤를 이었다. 이러한 인체표면 온도분포 결과를 토대로, 본 연구에서는 열에너지 수확의류 개발을 위한 기본 지침을 도출하였다.

• 한국지능시스템학회논문지
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• 제27권1호
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• pp.1-6
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• 2017

최근의 에너지 하베스팅(energy harvesting) 무선 네트워크에 대한 연구는 제한된 에너지 자원 문제를 해결하여 효율적으로 네트워크 수명을 연장할 수 있는 기법 개발에 집중되고 있다. 에너지 하베스팅을 통해 획득할 수 있는 에너지의 양과 효율을 향상시키기 위해서는 여러 가지 에너지 하베스팅 특성을 종합적으로 고려하여 에너지 획득과 데이터 전송을 병행하는 네트워크 구조를 설계하는 매우 중요하다. 본 논문에서는 수신측에서 간섭 정보와 충전 시간을 고려하여 네트워크 내의 에너지 하베스팅 용량을 최대화하면서 종단간 지연 시간을 최소화할 수 있는 간섭 기반의 충전 인지 라우팅 프로토콜(ICARP)을 제안한다. 이를 위해 기회적 에너지 하베스팅 무선 네트워크에서 종단간 지연시간을 최소화할 수 있도록 충전 시간을 패킷 전달의 지연 성분을 적용한 새로운 간섭 기반 충전 인지 라우팅 기준(routing metric)과 ICARP를 설계하였다. 본 논문에서 제시한 라우팅 기법을 통한 전달 지연시간의 단축은 패킷손실이나 재전송으로 인한 에너지 소비량을 줄이는 효과를 얻을 수 있다. 시뮬레이션을 이용한 성능평가를 통하여 제안된 기법이 기존의 라우팅 기법보다 패킷전달율과 종단간 지연시간 측면에서 성능이 향상됨을 보였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2017년도 춘계학술대회
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• pp.735-737
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• 2017

An Off grid or remote solar electric systems are an energy supply to our home or to our companies without the utility of Grid at all. Off grid solar systems are very important for those who live in remote locations especially for developing countries where getting the electric grid is extremely expensive, inconvenient or for those who doesn't need to pay a monthly bill with the electric bill in general. The main critical components of any solar power system or renewable energy harvesting systems are the energy storage systems and its charge controller system. Energy storage systems are the essential integral part of a solar energy harvesting system and in general for all renewable energy harvesting systems. To provide an optimal solution of both high power density and high energy density at the same time we have to use hybrid energy storage systems (HESS), that combine two or more energy storage technologies with complementary characteristics. In this present work, design and simulation we use two storage systems supercapacitor for high power density and lithium based battery for high energy density. Here the system incorporates fast-response supercapacitors to provide power to manage solar smoothing and uses a battery for load shifting. On this paper discuss that the total energy throughout of the battery is much reduced and the typical thermal stresses caused by high discharge rate responses are mitigated by integrating supercapacitors with the battery storage system. In addition of the above discussion the off grid solar electric energy harvesting presented in this research paper includes battery and supercapacitor management system, MPPT (maximum power point tracking) system and back/boost convertors. On this present work the entire model of off grid electric energy harvesting system and all other functional blocks of that system is implemented in MATLAB Simulink.

• 한국위성정보통신학회논문지
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• 제10권4호
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• pp.71-76
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• 2015

본 연구는 LTE, 5G의 무선 통신네트워크망에서 효율적으로 무선에너지하비스팅과 데이터 전송 실시하기 위한 시스템 모델을 제시한다. 수신 된 신호의 파워를 타임 스위칭(Time Switching)과 파워 스플릿팅(Power Splitting) 기법을 통해 우리가 원하는 무선에너지하비스팅 효율과 데이터 전송률을 만족시키기 위한최적의 타암 & 파워 비율을 찾는다. 그래서 최적의 시간 & 파워 비율을 선정함으로써 우리는 효율적으로 데이터 전송과 에너지하비스팅이 가능하다. 또 이상적인 수신기와 제안한 시스템 모델의 비교를 통해 성능 분석을 실시하고, 앞으로의 연구방향을 제시한다.

• 한국분말재료학회지
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• 제27권3호
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• pp.247-255
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• 2020

Recently, interest in technology for eco-friendly energy harvesting has been increasing. Polyvinylidene fluoride (PVDF) is one of the most fascinating materials that has been used in energy harvesting technology as well as micro-filters by utilizing an electrostatic effect. To enhance the performance of the electrostatic effect-based nanogenerator, most studies have focused on enlarging the contact surface area of the pair of materials with different triboelectric series. For this reason, one-dimensional nanofibers have been widely used recently. In order to realize practical energy-harvesting applications, PVDF nanofibers are modified by enlarging their contact surface area, modulating the microstructure of the surface, and maximizing the fraction of the ν-phase by incorporating additives or forming composites with inorganic nanoparticles. Among them, nanocomposite structures incorporating various nanoparticles have been widely investigated to increase the β-phase through strong hydrogen bonding or ion-dipole interactions with -CF₂/CH₂- of PVDF as well as to enhance the mechanical strength. In this study, we report the recent advances in the nanocomposite structure of PVDF nanofibers and inorganic nanopowders.

• 한국재료학회지
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• 제25권10호
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• pp.523-530
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• 2015

Electricity generation through fossil fuels has caused environmental pollution. To solve this problem, research on new renewable energy (solar, wind, geothermal heat, etc.) to replace fossil fuels is in progress. These devices are able to consistently generate power. However, they have many drawbacks, such as high installation costs and limitations in possible set-up environments. Thus, piezoelectric harvesting technology, which is able to overcome the limitations of existing energy technologies, is actively being studied. Piezoelectric harvesting technology uses the piezoelectric effect which occurs in crystals that generate voltage when stress is applied. Therefore, it has advantages such as a wider installation base and lower technological cost. In this study, a piezoelectric energy harvesting device based on constant wave motion was investigated. This device can regenerate electricity in a constant turbulent flow in the middle of the sea. The components of the device are circuitry, a steel bar, an bimorph piezoelectric element and buoyancy elements. In addition, a multiphysical analysis coupled with the structure and piezoelectric elements was conducted to estimate the performance of the device. With this piezoelectric energy harvesting device, the displacement and electric power were analyzed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권9호
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• pp.3075-3093
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• 2014

In this paper, we consider an advanced wireless user, called primary-secondary user (PSU) who is capable of harvesting renewable energy and connecting to both the primary network and cognitive radio networks simultaneously. Recently, energy harvesting has received a great deal of attention from the research community and is a promising approach for maintaining long lifetime of users. On the other hand, the cognitive radio function allows the wireless user to access other primary networks in an opportunistic manner as secondary users in order to receive more throughput in the current time slot. Subsequently, in the paper we propose the channel access policy for a PSU with consideration of the energy harvesting, based on a Partially Observable Markov decision process (POMDP) in which the optimal action from the action set will be selected to maximize expected long-term throughput. The simulation results show that the proposed POMDP-based channel access scheme improves the throughput of PSU, but it requires more computations to make an action decision regarding channel access.