Optimal Geometry of Holes in a Cable Tray for Offshore Plants

Daehoon Park,Jangmyung Lee 한국전자파학회JEES 2021 Journal of Electromagnetic Engineering and Science Vol.21 No.4

This study analyzes the crosstalk effects caused by the geometry of holes in a cable tray in offshore plants. Using the analysis results, we determine the optimal hole geometry that can effectively reduce the tray weight under minimum crosstalk. It was previously shown that metal cable trays can reduce crosstalk among cables. However, the impact of hole geometry was not considered. This study demonstrates the impact of hole geometry on the crosstalk. In addition, an algorithm is proposed to determine the optimal geometry of holes in the cable tray. The simulation results validate the proposed algorithm and can be useful for the designers of cable trays with holes.

Analog reversible nonvolatile memcapacitance in metal-oxide-semiconductor memcapacitor with ITO/HfO_x/Si structure

Park, Daehoon,Yang, Paul,Kim, Hyung Jun,Beom, Keonwon,Lee, Hyun Ho,Kang, Chi Jung,Yoon, Tae-Sik American Institute of Physics 2018 APPLIED PHYSICS LETTERS Vol.113 No.16

Ferroelectric nanoparticle-embedded sponge structure triboelectric generators

Park, Daehoon,Shin, Sung-Ho,Yoon, Ick-Jae,Nah, Junghyo IOP 2018 Nanotechnology Vol.29 No.18

<P>We report high-performance triboelectric nanogenerators (TENGs) employing ferroelectric nanoparticles (NPs) embedded in a sponge structure. The ferroelectric BaTiO<SUB>3</SUB> NPs inside the sponge structure play an important role in increasing surface charge density by polarized spontaneous dipoles, enabling the packaging of TENGs even with a minimal separation gap. Since the friction surfaces are encapsulated in the packaged device structure, it suffers negligible performance degradation even at a high relative humidity of 80%. The TENGs also demonstrated excellent mechanical durability due to the elasticity and flexibility of the sponge structure. Consequently, the TENGs can reliably harvest energy even under harsh conditions. The approach introduced here is a simple, effective, and reliable way to fabricate compact and packaged TENGs for potential applications in wearable energy-harvesting devices.</P>

Reversible capacitance changes in the MOS capacitor with an ITO/CeO₂/p-Si structure

Park, Daehoon,Kim, Minju,Beom, Keonwon,Cho, Seong-Yong,Kang, Chi Jung,Yoon, Tae-Sik Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.786 No.-

<P><B>Abstract</B></P> <P>A reversible capacitance changes with respect to the polarity of applied voltage is demonstrated in a MOS (metal-oxide-semiconductor) capacitor consisting of a high-k CeO<SUB>2</SUB> and oxygen-reactive indium-tin-oxide (ITO) electrode on p-Si substrate, i.e., an ITO/CeO<SUB>2</SUB>/p-Si structure. The capacitance-voltage (<I>C</I>-<I>V</I>), capacitance-time (<I>C</I>-<I>t</I>), and voltage-pulse measurements exhibit consistently that the accumulation capacitance is gradually increased upon repeatedly applying negative voltage to the ITO, while the depletion capacitance is reversibly decreased upon applying positive voltage. Particularly, the capacitance change is observed even at a low voltage of ±0.5 V from the device with 40-nm-thick CeO<SUB>2</SUB> layer. The capacitance change is further enhanced as increasing measurement temperature from 25 to 100 °C, implying that the capacitance change is associated with the thermally activated process under the applied voltage. In addition, the resistance of ITO gate electrode is found to decrease upon applying negative voltage, but it is increased reversibly upon applying positive voltage. The reversible capacitance changes in the MOS capacitor with oxygen-reactive ITO gate electrode are explained with voltage-driven oxygen ion migration between ITO and CeO<SUB>2</SUB> layers that can alter the CeO<SUB>2</SUB> dielectric permittivity and induce the gate depletion in the ITO. These reversible capacitance changes have a potential to be employed to modulate the MOSFET (MOS field-effect-transistor) properties such as on-state current, threshold voltage, and transconductance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polarity-dependent reversible capacitance changes in an ITO/CeO<SUB>2</SUB>/p-Si structure. </LI> <LI> Capacitance changes through voltage-driven oxygen migration between ITO and CeO<SUB>2</SUB>. </LI> <LI> Application of reversible capacitance changes to modulate the MOSFET properties. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The influence of substrate-dependent triboelectric charging of graphene on the electric potential generation by the flow of electrolyte droplets

Park, Daehoon,Won, Sejeong,Kim, Kwang-Seop,Jung, Joo-Yun,Choi, Jang-Young,Nah, Junghyo Elsevier 2018 Nano energy Vol.54 No.-

<P><B>Abstract</B></P> <P>Generation of electric potential by the flow of an electrolyte droplet on a graphene surface is investigated to develop a liquid motion energy harvester. Most of the research efforts to date have been focused on unveiling the interaction between graphene and an electrolyte droplet. However, other factors that significantly affect the output potential have not been paid much attention. Here, we report the electrostatic charging of graphene during a layer-transfer process and its influence on the enhancement of the performance of graphene-based liquid motion energy harvesting devices. In particular, we investigated the dependence of the output voltage on the triboelectric properties of the substrate. Our finding indicates that the triboelectric surface charging of graphene is significantly influenced by physisorption between graphene and the underlying substrate. Therefore, it directly affects the output power generation and the concentration of electrolyte solution at which the maximum power generation can be achieved. The method presented here is a simple route to further improve the output performance of graphene-based liquid motion energy harvesting devices and this study extends the physical understanding of charge interaction between graphene and an electrolyte solution.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Triboelectrification of the graphene during the transfer process affects the performance of TENG. </LI> <LI> Interaction between the graphene and the substrate determines surface charging of the graphene. </LI> <LI> The origin of the output enhancement mechanism was experimentally investigated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A Design on the Image-based Indoor Automatic Flight Control of Quadcopter

Daehoon Park,Hyun Lee,Jang-Myung Lee 제어로봇시스템학회 2019 제어로봇시스템학회 국제학술대회 논문집 Vol.2019 No.10

In this paper, we proposed image based indoor automatic flight system of quadcopter to follow a user defined flight guideline on the floor by utilizing its own camera installed in the bottom of the drone for autonomous indoor flight of the quadcopter system. For this paper, we configure the hardware with quadcopter and GCS using notebook. GCS analyzes the sensor signals including image signal from quadcopter and send motor command signal to quadcopter. The autonomous flight algorithm is divided into an image processing system and a drone control system. This system analyzed the image signal from drone camera, and estimated direction and position of the guideline, and sent motor commands to drone. We verified the image based automatic flight control system by modeling and simulation. We confirmed that the quadcopter was autonomous flying properly along the guideline on the floor by modeling and simulation.

Role of a buried indium zinc oxide layer in the performance enhancement of triboelectric nanogenerators

Park, Daehoon,Lee, Sol,Anh, Cao Viet,Park, Pangun,Nah, Junghyo Elsevier 2019 Nano energy Vol.55 No.-

<P><B>Abstract</B></P> <P>Generally, triboelectric generators (TENGs) demonsrate a considerably lower output current than output voltage; this has largely limited their performance enhancement. Thus, enormous research efforts have been made to address this problem. In this work, we present a simple method to enhance the triboelectric output current by burying an indium zinc oxide (IZO) layer under the triboelectric polymer friction layer. The IZO layer provides large interface density of states, which function as a charge reservoir. During frictional contact-separation motion of the TENG, electrons can be stored in or pumped out of these states. By optimizing the properties of the IZO layer, the output performance of the TENG is greatly improved, generating an output power density of ~ 25 mW/cm<SUP>2</SUP>. Specifically, an output voltage and current density of ~ 140 V and ~ 180 μA/cm<SUP>2</SUP> were obtained, which are 4-fold and 9-fold higher, respectively, than a TENG without an IZO layer. The method introduced here suffers less from friction layer wear-out and can effectively enhance the performance of TENGs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report the performance enhancement of TENG by burying a metal oxide semiconductor (IZO) under the frictional surface, which contributes substantial increase of output current </LI> <LI> The roles of a buried IZO layer on the performance enhancement of TENG were investigated. </LI> <LI> The optimal composition and fabrication process of the IZO layer were determined for the TENG. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

마이크로 어레이 데이터에 적용된 2단계 K-means 클러스터링의 소개

박대훈(Daehoon Park),김연태(Yountae Kim),김성신(Sungshin Kim),이춘환(Choon-Hwan Lee) 한국지능시스템학회 2007 한국지능시스템학회논문지 Vol.17 No.2

많은 유전자 정보와 그 부산물은 많은 방법을 통해 연구되어 왔다. DNA 마이크로어레이 기술의 사용은 많은 데이터를 가져왔으며, 이렇게 얻은 데이터는 기존의 연구 방법으로는 분석하기 힘들다. 본 눈문에서는 많은 양의 데이터를 처리할 수 있게 하기 위하여 K-means 클러스터링 알고리즘을 이용한 분할 클러스터링을 제안하였다. 제안한 방법을 쌀 유전자로부터 나온 마이크로어레이 데이터에 적용함으로써 제안된 클러스터링 방법의 유용성을 검증하였으며, 기존의 K-means 클러 스터링 알고리즘을 적용한 결과와 비교함으로써 제안된 알고리즘의 우수성을 확인할 수 있었다. Long gene sequences and their products have been studied by many methods. The use of DNA(Deoxyribonucleic acid) microarray technology has resulted in an enormous amount of data, which has been difficult to analyze using typical research methods. This paper proposes that mass data be analyzed using division clustering with the K-means clustering algorithm. To demonstrate the superiority of the proposed method, it was used to analyze the microarray data from rice DNA. The results were compared to those of the existing K-meansmethod establishing that the proposed method is more useful in spite of the effective reduction of performance time.

Geometry transformation and alterations of periodically patterned Si nanotemplates by dry oxidation

Park, Jeongwon,Chen, Li-Han,Hong, Daehoon,Choi, Chulmin,Loya, Mariana,Brammer, Karla,Bandaru, Prab,Jin, Sungho IOP Pub 2009 Nanotechnology Vol.20 No.1

<P>We report on the size-dependent transformation and geometrical modifications of periodically patterned Si templates by a combination of dry oxidation and chemical etching. Deep ultraviolet lithography patterned circular holes with diameters varying between 190 nm and 1 µm on Si wafers were oxidized at 1000 °C using dry oxygen for various durations, with selected samples chemically etched for oxide removal for additional alterations. An interesting phenomenon of a circular-to-square shape transformation of the holes was observed, which was particularly pronounced in the sub-200 nm regime. We tentatively attribute the change to the surface energy and geometry constraints in nanoscale patterns. </P>

Subwavelength silicon through-hole arrays as an all-dielectric broadband terahertz gradient index metamaterial (4 pages)

Park, Sang-Gil,Lee, Kanghee,Han, Daehoon,Ahn, Jaewook,Jeong, Ki-Hun AMERICAN INSTITUTE OF PHYSICS 2014 APPLIED PHYSICS LETTERS Vol.105 No.9