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Prof. Junghyo Nah
Chungnam National University, Republic of Korea

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0 nanowire
0 piezoelectric energy harvesting
0 piezoelectric ceramics
0 Triboelectric Nano generator
0 Nanowire FETs

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nanowire
triboelectric
air filter
piezoelectric energy harvesting
Nanowire FETs
nanofiber membrane

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Journal article
Published: 20 August 2021 in Applied Sciences
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In general, high-speed machines should be designed to satisfy electromagnetic and mechanical characteristics. In this study, the design of high-speed permanent magnet synchronous generator with two different shaft materials considering overhang effect and mechanical characteristics was performed. It was confirmed that the leakage magnetic flux generated by the two shaft materials electromagnetically affects the high-speed generator. Additionally, it is important to accurately predict the natural frequency mode and critical speed to prevent damage and vibration of the rotating body owing to scattering during high-speed rotation. Therefore, the mechanical characteristics of the designed model were analyzed. In this study, we propose a design method that considers both the electromagnetic effects and mechanical characteristics. Subsequently, verification was performed through experiments and comparisons for the validity and reliability of the proposed design method.

ACS Style

Jeong-In Lee; Tae-Kyoung Bang; Hoon-Ki Lee; Jong-Hyeon Woo; Junghyo Nah; Jang-Young Choi. Design of the High-Speed PMSG with Two Different Shaft Material Considering Overhang Effect and Mechanical Characteristics. Applied Sciences 2021, 11, 7670 .

AMA Style

Jeong-In Lee, Tae-Kyoung Bang, Hoon-Ki Lee, Jong-Hyeon Woo, Junghyo Nah, Jang-Young Choi. Design of the High-Speed PMSG with Two Different Shaft Material Considering Overhang Effect and Mechanical Characteristics. Applied Sciences. 2021; 11 (16):7670.

Chicago/Turabian Style

Jeong-In Lee; Tae-Kyoung Bang; Hoon-Ki Lee; Jong-Hyeon Woo; Junghyo Nah; Jang-Young Choi. 2021. "Design of the High-Speed PMSG with Two Different Shaft Material Considering Overhang Effect and Mechanical Characteristics." Applied Sciences 11, no. 16: 7670.

Journal article
Published: 09 July 2021 in Applied Sciences
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Recently, three-dimensional printing (3DP) technology has been widely adopted in biology and biomedical applications, thanks to its capacity to readily construct complex 3D features. Using hot-melt extrusion 3DP, scaffolds for bone tissue engineering were fabricated using a composite of biodegradable polycaprolactone (PCL) and hydroxyapatite (HA). However, there are hardly any published reports on the application of the fused deposition modeling (FDM) method using feed filaments, which is the most common 3D printing method. In this study, we report on the fabrication and characterization of biocompatible filaments made of polycaprolactone (PCL)/hydroxyapatite (HA), a raw material mainly used for bone scaffolds, using FDM 3D printing. A series of filaments with varying HA content, from 5 to 25 wt.%, were fabricated. The mechanical and electrical properties of the various structures, printed using a commercially available 3D printer, were examined. Specifically, mechanical tensile tests were performed on the 3D-printed filaments and specimens. In addition, the electrical dielectric properties of the 3D-printed structures were investigated. Our method facilitates the fabrication of biocompatible structures using FDM-type 3DP, creating not only bone scaffolds but also testbeds for mimicking bone structure that may be useful in various fields of study.

ACS Style

Chang Kim; Kyung Han; Sol Lee; Min Kim; Soo Kim; Junghyo Nah. Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds. Applied Sciences 2021, 11, 6351 .

AMA Style

Chang Kim, Kyung Han, Sol Lee, Min Kim, Soo Kim, Junghyo Nah. Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds. Applied Sciences. 2021; 11 (14):6351.

Chicago/Turabian Style

Chang Kim; Kyung Han; Sol Lee; Min Kim; Soo Kim; Junghyo Nah. 2021. "Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds." Applied Sciences 11, no. 14: 6351.

Research article
Published: 20 May 2021 in ACS Applied Materials & Interfaces
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As the demand for wireless sensors and equipment is unprecedentedly increasing, the interest in electromagnetic interference (EMI)-shielding materials that can effectively block accompanying electromagnetic interference is also constantly increasing. In particular, flexible and lightweight EMI-shielding materials that exhibit high EMI-shielding effectiveness (SE) have been more actively investigated as they are applicable to various applications. In this work, we reported the fabrication and performance of conducting polymer nanofiber EMI-shielding material, which was realized using electrospun polyvinylidene fluoride (PVDF) core–shell nanofiber membranes with highly conductive shells. Using the chemical polymerization method, core–shell nanofibers with highly conductive shells were employed without compositing with conductive fillers, resulting in shell-conductive lightweight EMI-shielding material without impairing the original properties of the nanofiber. In particular, thanks to the nanofiber structure, the EMI-shielding material exhibits superb flexibility, and the EMI SE was also improved through the enhanced absorption of EM waves and multireflections by the porous nanofiber film structure. Specifically, the developed EMI-shielding material in this work exhibited a SE of ∼40 dB in the X-band, which corresponds to an absolute shielding effectiveness (SSEt) of 16,230 dB·cm2/g at a thickness of 14 μm. Moreover, the high durability and hydrophobicity of the PVDF nanofibers with poly (3,4-ethylenedioxythiophene) (PEDOT)-polymerized shell can also be useful in practical applications.

ACS Style

Sol Lee; Joomin Park; Min Cheol Kim; Minje Kim; Pangun Park; Ick-Jae Yoon; Junghyo Nah. Polyvinylidene Fluoride Core–Shell Nanofiber Membranes with Highly Conductive Shells for Electromagnetic Interference Shielding. ACS Applied Materials & Interfaces 2021, 13, 25428 -25437.

AMA Style

Sol Lee, Joomin Park, Min Cheol Kim, Minje Kim, Pangun Park, Ick-Jae Yoon, Junghyo Nah. Polyvinylidene Fluoride Core–Shell Nanofiber Membranes with Highly Conductive Shells for Electromagnetic Interference Shielding. ACS Applied Materials & Interfaces. 2021; 13 (21):25428-25437.

Chicago/Turabian Style

Sol Lee; Joomin Park; Min Cheol Kim; Minje Kim; Pangun Park; Ick-Jae Yoon; Junghyo Nah. 2021. "Polyvinylidene Fluoride Core–Shell Nanofiber Membranes with Highly Conductive Shells for Electromagnetic Interference Shielding." ACS Applied Materials & Interfaces 13, no. 21: 25428-25437.

Research article
Published: 20 May 2021 in ACS Nano
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Recently, the inherent piezoelectric properties of the 2D transition-metal dichalcogenides (TMDs) tin monosulfide (SnS) and tin disulfide (SnS2) have attracted much attention. Thus the piezoelectricity of these materials has been theoretically and experimentally investigated for energy-harvesting devices. However, the piezoelectric output performance of the SnS2- or SnS-based 2D thin film piezoelectric nanogenerator (PENG) is still relatively low, and the fabrication process is not suitable for practical applications. Here we report the formation of the SnS2/SnS heterostructure thin film for the enhanced output performance of a PENG using atomic layer deposition (ALD). The piezoelectric response of the heterostructure thin film was increased by ∼40% compared with that of the SnS2 thin film, attributed to large band offset induced by the heterojunction formation. Consequently, the output voltage and current density of the heterostructure PENG were 60 mV and 11.4 nA/cm2 at 0.6% tensile strain, respectively. In addition, thickness-controllable large-area uniform thin-film deposition via ALD ensures that the reproducible output performance is achieved and that the output density can be lithographically adjusted depending on the applications. Therefore, the SnS2/SnS heterostructure PENG fabricated in this work can be employed to develop a flexible energy-harvesting device or an attachable self-powered sensor for monitoring pulse and human body movement.

ACS Style

Viet Anh Cao; Minje Kim; Weiguang Hu; Sol Lee; Sukhyeong Youn; Jiwon Chang; Hyo Sik Chang; Junghyo Nah. Enhanced Piezoelectric Output Performance of the SnS2/SnS Heterostructure Thin-Film Piezoelectric Nanogenerator Realized by Atomic Layer Deposition. ACS Nano 2021, 15, 10428 -10436.

AMA Style

Viet Anh Cao, Minje Kim, Weiguang Hu, Sol Lee, Sukhyeong Youn, Jiwon Chang, Hyo Sik Chang, Junghyo Nah. Enhanced Piezoelectric Output Performance of the SnS2/SnS Heterostructure Thin-Film Piezoelectric Nanogenerator Realized by Atomic Layer Deposition. ACS Nano. 2021; 15 (6):10428-10436.

Chicago/Turabian Style

Viet Anh Cao; Minje Kim; Weiguang Hu; Sol Lee; Sukhyeong Youn; Jiwon Chang; Hyo Sik Chang; Junghyo Nah. 2021. "Enhanced Piezoelectric Output Performance of the SnS2/SnS Heterostructure Thin-Film Piezoelectric Nanogenerator Realized by Atomic Layer Deposition." ACS Nano 15, no. 6: 10428-10436.

Research article
Published: 14 April 2021 in ACS Applied Materials & Interfaces
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The evolution of “smart life,” which connects all internet-of-things (IoT) microdevices and microsensors under wireless communication grids, requires microscale energy storage devices with high power and energy density and long-term cyclability to integrate them with sustainable power generators. Instead of Li-ion batteries with a short lifetime, pseudocapacitors with longer or infinite cyclability and high-power density have been considered as efficient energy storage devices for IoT. However, the design and fabrication of microscale pseudocapacitors have difficulties in patterning microscale electrodes when loading active materials at specific points of the electrodes using conventional microfabrication methods. Here, we developed a facile, one-step fabrication method of micro-supercapacitors (MSCs) through the in situ formation of Co metals and the reduced graphene oxides (rGOs) in a one-pot laser scribing process. The prepared Co/rGO MSC thus exhibited four times higher capacitance than the rGO MSC, due to the Faradaic charge capacitance behavior of the Co/rGO composites.

ACS Style

Sang Hwa Lee; Jungjun Lee; Jaemin Jung; A Ra Cho; Jae Ryeol Jeong; Cu Dang Van; Junghyo Nah; Min Hyung Lee. Enhanced Electrochemical Performance of Micro-Supercapacitors Via Laser-Scribed Cobalt/Reduced Graphene Oxide Hybrids. ACS Applied Materials & Interfaces 2021, 13, 18821 -18828.

AMA Style

Sang Hwa Lee, Jungjun Lee, Jaemin Jung, A Ra Cho, Jae Ryeol Jeong, Cu Dang Van, Junghyo Nah, Min Hyung Lee. Enhanced Electrochemical Performance of Micro-Supercapacitors Via Laser-Scribed Cobalt/Reduced Graphene Oxide Hybrids. ACS Applied Materials & Interfaces. 2021; 13 (16):18821-18828.

Chicago/Turabian Style

Sang Hwa Lee; Jungjun Lee; Jaemin Jung; A Ra Cho; Jae Ryeol Jeong; Cu Dang Van; Junghyo Nah; Min Hyung Lee. 2021. "Enhanced Electrochemical Performance of Micro-Supercapacitors Via Laser-Scribed Cobalt/Reduced Graphene Oxide Hybrids." ACS Applied Materials & Interfaces 13, no. 16: 18821-18828.

Journal article
Published: 27 February 2021 in Ceramics International
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In this study, we examined the dependence of surface morphology and spin Seebeck effect (SSE) voltages on the poly[vinylpyrrolidone] (PVP) concentration in polycrystalline Y3Fe5O12 (YIG) ultrathin films on a silicon substrate synthesized by metal-organic decomposition followed by a crystallization process. During fabrication, PVP concentrations of 0.5–2 g were used while all other conditions remained fixed. Atomic force microscopy and grazing incidence X-ray diffraction (XRD) measurements revealed a strong dependence of crystallinity and sample morphology on PVP concentration. The 1-g PVP sample had the smoothest surface, with a root mean square roughness of 0.2 nm, as well as superior bulk uniformity with respect to the shape and intensity of XRD reflection peaks. This was confirmed by scanning electron microscopy measurements of a cross-section of the sample that revealed a uniform film without pores. SSE measurements were performed to obtain the output SSE voltages (VSSE) of all samples, to which a platinum layer was added as a spin-detection layer. Repeatedly, the 1-g PVP sample had the best performance, demonstrating the importance of film crystallinity and morphology in the spin-to-charge conversion efficiency of YIG films.

ACS Style

Trinh Nguyen Thi; Phuoc Cao Van; Duc Duong Viet; Viet Dong Quoc; Hayeong Ahn; Viet Anh Cao; Min-Gu Kang; Junghyo Nah; Byong-Guk Park; Jong-Ryul Jeong. Morphology-dependent spin Seebeck effect in yttrium iron garnet thin films prepared by metal-organic decomposition. Ceramics International 2021, 47, 16770 -16775.

AMA Style

Trinh Nguyen Thi, Phuoc Cao Van, Duc Duong Viet, Viet Dong Quoc, Hayeong Ahn, Viet Anh Cao, Min-Gu Kang, Junghyo Nah, Byong-Guk Park, Jong-Ryul Jeong. Morphology-dependent spin Seebeck effect in yttrium iron garnet thin films prepared by metal-organic decomposition. Ceramics International. 2021; 47 (12):16770-16775.

Chicago/Turabian Style

Trinh Nguyen Thi; Phuoc Cao Van; Duc Duong Viet; Viet Dong Quoc; Hayeong Ahn; Viet Anh Cao; Min-Gu Kang; Junghyo Nah; Byong-Guk Park; Jong-Ryul Jeong. 2021. "Morphology-dependent spin Seebeck effect in yttrium iron garnet thin films prepared by metal-organic decomposition." Ceramics International 47, no. 12: 16770-16775.

Conference paper
Published: 31 January 2021 in 2021 International Conference on Electronics, Information, and Communication (ICEIC)
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High operating temperature (HOT) infrared device plays a key role in decreasing the size, weight and power consumption (SWaP) of the infrared system. HOT detector enables miniaturization of the detector and longer lifetime of cooler. To realizing HOT infrared detector with $15\ \mu\mathrm{m}$ pitch video graphics array (VGA), we studied InAs/InAsSb T2SL nBn device. The fabricated focal plane arrays and detector exhibited the dark current characteristics and optical performance capable of operating from 80 to 140 K, respectively.

ACS Style

Young Ho Kim; Han Jung; Hyun Jin Lee; Junghyo Nah. HOT MWIR Detector Development with InAs/InAsSb T2SL nBn Structure. 2021 International Conference on Electronics, Information, and Communication (ICEIC) 2021, 1 -2.

AMA Style

Young Ho Kim, Han Jung, Hyun Jin Lee, Junghyo Nah. HOT MWIR Detector Development with InAs/InAsSb T2SL nBn Structure. 2021 International Conference on Electronics, Information, and Communication (ICEIC). 2021; ():1-2.

Chicago/Turabian Style

Young Ho Kim; Han Jung; Hyun Jin Lee; Junghyo Nah. 2021. "HOT MWIR Detector Development with InAs/InAsSb T2SL nBn Structure." 2021 International Conference on Electronics, Information, and Communication (ICEIC) , no. : 1-2.

Journal article
Published: 30 January 2021 in Applied Sciences
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In this work, we report on a flexible triboelectric generator (TEG) with a multilayer polymer structure, consisting of a poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) layer sandwiched by polydimethylsiloxane (PDMS) layers for the performance enhancement of TEGs. We confirmed that the output performance of the TEG is closely dependent on the structure and polarization direction of the PVDF-TrFE layer. In addition, the PDMS layer serves as the electron trapping layer and suppresses the discharging of the surface charges, boosting the output performance. Furthermore, the polarized PVDF-TrFE layer in the preferred direction contributes to increasing the surface potential during the contact–separation motion. The interaction between these two polymer layers synergistically leads to the boosted output performance of TEGs. Specifically, the maximum peak-to-peak output voltage and current density of 420 V and 50 μA/cm2 generated by the proposed architecture, representing approximately a fivefold improvement compared with the TEG with a single layer, even though the same friction layers were used for contact electrification.

ACS Style

Deahoon Park; Min Cheol Kim; Minje Kim; Pangun Park; Junghyo Nah. Performance Enhancement of Flexible Polymer Triboelectric Generator through Polarization of the Embedded Ferroelectric Polymer Layer. Applied Sciences 2021, 11, 1284 .

AMA Style

Deahoon Park, Min Cheol Kim, Minje Kim, Pangun Park, Junghyo Nah. Performance Enhancement of Flexible Polymer Triboelectric Generator through Polarization of the Embedded Ferroelectric Polymer Layer. Applied Sciences. 2021; 11 (3):1284.

Chicago/Turabian Style

Deahoon Park; Min Cheol Kim; Minje Kim; Pangun Park; Junghyo Nah. 2021. "Performance Enhancement of Flexible Polymer Triboelectric Generator through Polarization of the Embedded Ferroelectric Polymer Layer." Applied Sciences 11, no. 3: 1284.

Journal article
Published: 24 December 2020 in Infrared Physics & Technology
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InAsSb nBn structure plays a key role in realizing high operating temperature (HOT) MWIR detectors. However, the AlAsSb layer, functioning as a barrier layer, can be rapidly oxidized during the pixel isolation process, forming undesirable oxides that can contribute to increase the surface leakage current. In this work, electrical and optical analysis were performed to investigate the role of the post-treatment process after pixel isolation step in reducing the oxidation and inhibiting the formation of unfavorable oxides closely related to the surface leakage currents. Our study shows that H2O2 post-treatment after the dry pixel isolation process can effectively reduce the barrier oxidation and suppress the formation of Sb2O5, greatly reducing the surface leakage current. Using the proposed post-treatment process, the dark current density of less than 1 × 10−6 A/cm2 was obtained at an applied bias of −0.3 V and 150 K, which is one order of magnitude lower than that of the InAsSb nBn device recently reported.

ACS Style

Hyun Jin Lee; Sung Yong Ko; Young Ho Kim; Junghyo Nah. Surface leakage current reduction of InAsSb nBn MWIR HOT detector via hydrogen peroxide treatment. Infrared Physics & Technology 2020, 112, 103597 .

AMA Style

Hyun Jin Lee, Sung Yong Ko, Young Ho Kim, Junghyo Nah. Surface leakage current reduction of InAsSb nBn MWIR HOT detector via hydrogen peroxide treatment. Infrared Physics & Technology. 2020; 112 ():103597.

Chicago/Turabian Style

Hyun Jin Lee; Sung Yong Ko; Young Ho Kim; Junghyo Nah. 2020. "Surface leakage current reduction of InAsSb nBn MWIR HOT detector via hydrogen peroxide treatment." Infrared Physics & Technology 112, no. : 103597.

Journal article
Published: 18 November 2020 in IEEE Internet of Things Journal
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In the aeronautics industry, wireless avionics intra-communications have a tremendous potential to improve efficiency and flexibility while reducing weight, fuel consumption, and maintenance costs over traditional wired avionics systems. This survey starts with an overview of the major benefits and opportunities in the deployment of wireless technologies for critical applications in an aircraft. The current state-of-art is presented in terms of system classifications based on data rate demands and transceiver installation locations. We then discuss major technical challenges in the design and realization of the envisioned aircraft applications. Although wireless avionics intra-communication has aspects and requirements similar to mission-critical applications of industrial automation, it also has specific issues such as wireless channels, complex structures, operations, and safety of the aircraft that make this area of research self-standing and challenging. Existing wireless techniques are discussed to investigate the applicability of the current solutions for the critical operations of an aircraft. Specifically, IEEE 802.15.4-based and Bluetooth-based solutions are discussed for low data rate applications, whereas IEEE 802.11-based and UWB-based solutions are considered for high data rate applications. We conclude the survey by highlighting major research directions in this emerging area.

ACS Style

Pangun Park; Piergiuseppe Di Marco; Junghyo Nah; Carlo Fischione. Wireless Avionics Intracommunications: A Survey of Benefits, Challenges, and Solutions. IEEE Internet of Things Journal 2020, 8, 7745 -7767.

AMA Style

Pangun Park, Piergiuseppe Di Marco, Junghyo Nah, Carlo Fischione. Wireless Avionics Intracommunications: A Survey of Benefits, Challenges, and Solutions. IEEE Internet of Things Journal. 2020; 8 (10):7745-7767.

Chicago/Turabian Style

Pangun Park; Piergiuseppe Di Marco; Junghyo Nah; Carlo Fischione. 2020. "Wireless Avionics Intracommunications: A Survey of Benefits, Challenges, and Solutions." IEEE Internet of Things Journal 8, no. 10: 7745-7767.

Journal article
Published: 17 July 2020 in NPG Asia Materials
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The current design trends in the field of electronic devices involve efforts to make these devices smaller, thinner, lighter, and more flexible. The development of such systems is expected to further accelerate, resulting in the production of wearable and Internet-of-Things devices. In this respect, microenergy storage systems with high capacity and fast charge/discharge rates have become important power sources for such devices. In particular, interdigitated microsupercapacitors (MSCs) have exhibited remarkable potential as micropower sources owing to their fast charge/discharge processes, long cycle life, and high power density compared with microbatteries. Nevertheless, facile fabrication of MSCs using interdigitated electrodes remains challenging, as it requires selective decoration of electrodes with pseudocapacitive materials, such as transition metal oxides, to increase their capacitance. In the present study, we developed a simple method for fabricating MSCs involving in situ formation of interdigitated graphene electrodes and ZnO nanorods by photothermal conversion of graphene oxide (GO) and Zn precursors using infrared (IR) laser scribing. The fabricated MSCs exhibit a high stack capacitance of 3.90 F cm−3 and an energy density of 0.43 mWh cm−3. Notably, the capacity of the developed material is three times higher than those of previously reported MSCs made from the same type of graphene. In addition, the capacitance retention rate of the fabricated MSC is approximately 70% when measured over 10,000 charging–discharging cycles at a constant current, which evidently indicates a stable device performance.

ACS Style

Jaemin Jung; Jae Ryeol Jeong; Jungjun Lee; Sang Hwa Lee; Soo Young Kim; Myung Jun Kim; Junghyo Nah; Min Hyung Lee. In situ formation of graphene/metal oxide composites for high-energy microsupercapacitors. NPG Asia Materials 2020, 12, 1 -9.

AMA Style

Jaemin Jung, Jae Ryeol Jeong, Jungjun Lee, Sang Hwa Lee, Soo Young Kim, Myung Jun Kim, Junghyo Nah, Min Hyung Lee. In situ formation of graphene/metal oxide composites for high-energy microsupercapacitors. NPG Asia Materials. 2020; 12 (1):1-9.

Chicago/Turabian Style

Jaemin Jung; Jae Ryeol Jeong; Jungjun Lee; Sang Hwa Lee; Soo Young Kim; Myung Jun Kim; Junghyo Nah; Min Hyung Lee. 2020. "In situ formation of graphene/metal oxide composites for high-energy microsupercapacitors." NPG Asia Materials 12, no. 1: 1-9.

Research article
Published: 05 May 2020 in ACS Applied Materials & Interfaces
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There is a growing interest in window air filters to protect indoor air quality from ultrafine particulate matter (PM) in outdoor air. The filters for this purpose must achieve high filtering efficiency without compromising the original functions of the window, such as high air permeability and visibility. Several filters meeting these requirements have been developed and demonstrate a high PM2.5 filtering efficiency. However, these filters are installed outside the window or on the window screen guard, thereby requiring high levels of ultraviolet (UV), chemical, and thermal resistance. These requirements have been overlooked so far. In this study, we examine the fabrication and performance of a polybenzimidazole-benzophenone (PBI-BP) composite nanofiber air filter, which demonstrates superb UV resistance, and chemical and thermal durability. Owing to the UV absorbance of the BP in the nanofibers, the filter membrane is robust even under prolonged UV exposure, which is essential for filters for this purpose. The filter membrane is not damaged even after treatment in strong acids or annealing at high temperature up to 400 ºC. Thus, the PBI-BP composite filter is suitable for practical application in window air filters and can also be adapted to develop filters used under other harsh environments.

ACS Style

Sol Lee; Kyung Seok Han; Minje Kim; Min Cheol Kim; Cao Viet Anh; Junghyo Nah; Viet Anh Cao. Polybenzimidazole–Benzophenone Composite Nanofiber Window Air Filter with Superb UV Resistance and High Chemical and Thermal Durability. ACS Applied Materials & Interfaces 2020, 12, 23914 -23922.

AMA Style

Sol Lee, Kyung Seok Han, Minje Kim, Min Cheol Kim, Cao Viet Anh, Junghyo Nah, Viet Anh Cao. Polybenzimidazole–Benzophenone Composite Nanofiber Window Air Filter with Superb UV Resistance and High Chemical and Thermal Durability. ACS Applied Materials & Interfaces. 2020; 12 (21):23914-23922.

Chicago/Turabian Style

Sol Lee; Kyung Seok Han; Minje Kim; Min Cheol Kim; Cao Viet Anh; Junghyo Nah; Viet Anh Cao. 2020. "Polybenzimidazole–Benzophenone Composite Nanofiber Window Air Filter with Superb UV Resistance and High Chemical and Thermal Durability." ACS Applied Materials & Interfaces 12, no. 21: 23914-23922.

Journal article
Published: 06 March 2020 in Nano Energy
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Recently, human motion and respiration monitoring sensors have attracted significant research attention in the field of wearable electronics and healthcare applications. Fiber-based electronic sensors demonstrate significant potential for such applications due to their flexibility. However, the superior flexibility of fiber-based sensors is generally limited due to the partial use of rigid elements such as metal electrode layers. In this paper, a simple method is presented for the fabrication of all-nanofiber multifunctional sensors, which consist of triboelectric (TE), piezoresistive (PR), and thermoresistive (TR) sensing elements and demonstrate superior flexibility, excellent wearability, and multifunctionality. The TE sensing unit was fabricated by integrating two triboelectrically dissimilar nanofiber surfaces using a polymer mesh separator, for the formation of internal macro-scale air gaps; followed by the electrical polarization of nanofibers. The TR and PR sensing elements were realized using vapor-phase polymerized fiber electrode layers. Using the sensor developed in this study, different motions and breathing frequencies can be individually or simultaneously detected using the TE, PR, and TR sensing elements. This work therefore presents a novel scheme for human motion sensors and breathing sensors, which are widely applicable to wearable electronics, healthcare monitoring, and human-machine interfaces.

ACS Style

Mehebub Alam; Sol Lee; Minje Kim; Kyung Seok Han; Viet Anh Cao; Junghyo Nah. Ultra-flexible nanofiber-based multifunctional motion sensor. Nano Energy 2020, 72, 104672 .

AMA Style

Mehebub Alam, Sol Lee, Minje Kim, Kyung Seok Han, Viet Anh Cao, Junghyo Nah. Ultra-flexible nanofiber-based multifunctional motion sensor. Nano Energy. 2020; 72 ():104672.

Chicago/Turabian Style

Mehebub Alam; Sol Lee; Minje Kim; Kyung Seok Han; Viet Anh Cao; Junghyo Nah. 2020. "Ultra-flexible nanofiber-based multifunctional motion sensor." Nano Energy 72, no. : 104672.

Journal article
Published: 20 February 2020 in IEEE Transactions on Applied Superconductivity
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Rotor eccentricity occurs during manufacturing, causing the de-vice to vibrate and make noise, thereby shortening its life. Its characteristics can be analyzed via the existing finite element method (FEM); however, analyzing characteristics according to design variables is time-consuming. Therefore, we implemented an analytical method that can rapidly identify the characteristics according to the design variables. We derived the magnetic flux density, the back-electromotive force, and the torque through the analytical method according to rotor eccentricity. The rotor eccen-tricity was considered to be based on the perturbation and the electromagnetic theories; accordingly, the governing equations and boundary conditions were derived. The analytical method was validated through FEM and experimental result.

ACS Style

Hoon-Ki Lee; Kyung-Hun Shin; Tae-Kyoung Bang; Jung-Hyo Nah; Jang-Young Choi. Experimental Verification and Analytical Study of Influence of Rotor Eccentricity on Electromagnetic Characteristics of Permanent Magnet Machine. IEEE Transactions on Applied Superconductivity 2020, 30, 1 -5.

AMA Style

Hoon-Ki Lee, Kyung-Hun Shin, Tae-Kyoung Bang, Jung-Hyo Nah, Jang-Young Choi. Experimental Verification and Analytical Study of Influence of Rotor Eccentricity on Electromagnetic Characteristics of Permanent Magnet Machine. IEEE Transactions on Applied Superconductivity. 2020; 30 (4):1-5.

Chicago/Turabian Style

Hoon-Ki Lee; Kyung-Hun Shin; Tae-Kyoung Bang; Jung-Hyo Nah; Jang-Young Choi. 2020. "Experimental Verification and Analytical Study of Influence of Rotor Eccentricity on Electromagnetic Characteristics of Permanent Magnet Machine." IEEE Transactions on Applied Superconductivity 30, no. 4: 1-5.

Journal article
Published: 18 November 2019 in Nano Energy
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To date, several attempts have been made to improve the performance of triboelectric nanogenerators (TENGs). Although notable advancements have been made in the output power density, it is still relatively low and further improvement in the output power density has been limited by air breakdown issue. In this work, we proposed preferable composite structures and an electrical activation method to maximize the output performance of TENGs by adopting ferroelectric composite interfacial layer. Specifically, by doping Nylon 11 with Poly (methyl methacrylate) - PMMA, we intensified the positive triboelectricity of Nylon 11 and simultaneously improved its physical durability. The negative triboelectricity of PVDF-TrFE was also enhanced by compositing with ZrO2 nanoparticles (NPs). Triboelectricity of both polymer composites was further boosted by polarizing them in favorable direction. Therefore, high frictional surface charge density of 220 μC/m2 was achieved in short-circuit condition, effectively promoting charge outputs. Consequently, the open circuit voltage and short circuit current density of ~500 V and ~500 μA cm−2 were achieved, respectively, exhibiting a remarkable output power density of ~42 mW cm−2.

ACS Style

Viet Anh Cao; Sol Lee; Minje Kim; Mehebub Alam; Pangun Park; Junghyo Nah. Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers. Nano Energy 2019, 67, 104300 .

AMA Style

Viet Anh Cao, Sol Lee, Minje Kim, Mehebub Alam, Pangun Park, Junghyo Nah. Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers. Nano Energy. 2019; 67 ():104300.

Chicago/Turabian Style

Viet Anh Cao; Sol Lee; Minje Kim; Mehebub Alam; Pangun Park; Junghyo Nah. 2019. "Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers." Nano Energy 67, no. : 104300.

Journal article
Published: 15 July 2019 in Advanced Functional Materials
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ACS Style

Kyung Seok Han; Sol Lee; Minje Kim; Pangun Park; Min Hyung Lee; Junghyo Nah. Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM 1.0 Filtration. Advanced Functional Materials 2019, 29, 1 .

AMA Style

Kyung Seok Han, Sol Lee, Minje Kim, Pangun Park, Min Hyung Lee, Junghyo Nah. Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM 1.0 Filtration. Advanced Functional Materials. 2019; 29 (37):1.

Chicago/Turabian Style

Kyung Seok Han; Sol Lee; Minje Kim; Pangun Park; Min Hyung Lee; Junghyo Nah. 2019. "Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM 1.0 Filtration." Advanced Functional Materials 29, no. 37: 1.

Journal article
Published: 29 March 2019 in Sensors
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The stability guarantee of wireless networked control systems is still challenging due to the complex interaction among the layers and the vulnerability to network faults, such as link and node failures. In this paper, we propose a robust wireless sensor and actuator network (R-WSAN) to maintain the control stability of multiple plants over the spatial-temporal changes of wireless networks. The proposed joint design protocol combines the distributed controller of control systems and the clustering, resource scheduling, and control task sharing scheme of wireless networks over a hierarchical cluster-based network. In particular, R-WSAN decouples the tasks from the inherently unreliable nodes and allows control tasks to share between nodes of wireless networks. Our simulations demonstrate that R-WSAN provides the enhanced resilience to the network faults for sensing and actuation without significantly disrupting the control performance.

ACS Style

Bongsang Park; Junghyo Nah; Jang-Young Choi; Ick-Jae Yoon; Pangun Park. Robust Wireless Sensor and Actuator Networks for Networked Control Systems. Sensors 2019, 19, 1535 .

AMA Style

Bongsang Park, Junghyo Nah, Jang-Young Choi, Ick-Jae Yoon, Pangun Park. Robust Wireless Sensor and Actuator Networks for Networked Control Systems. Sensors. 2019; 19 (7):1535.

Chicago/Turabian Style

Bongsang Park; Junghyo Nah; Jang-Young Choi; Ick-Jae Yoon; Pangun Park. 2019. "Robust Wireless Sensor and Actuator Networks for Networked Control Systems." Sensors 19, no. 7: 1535.

Research article
Published: 15 March 2019 in ACS Nano
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Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a novel method to remarkably increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS2 composite. Specifically, by compositing bulk MoS2 flakes with both Nylon 11 and PVDF-TrFE, respectively, charge density of each triboelectric charging surface was significantly increased. In addition, proper polarization of both ferroelectric composite layers has also led to an additional increase in the charge density. Combination of them synergistically increases the surface charge density, generating huge output current and the power output density. By optimizing the fabrication process, the output voltage and current density up to ~145 V and ~350 A/cm2 were achieved, respectively. Consequently, the TENG exhibits a recordable output power density of ~ 50 mW/cm2, which is one of the highest output power densities reported to date. The method introduced in this work can greatly increase the output current density of TENGs, facilitating the development of high performance triboelectric energy harvesting devices.

ACS Style

Minje Kim; Daehoon Park; Mehebub Alam; Sol Lee; Pangun Park; Junghyo Nah. Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS2 Composites. ACS Nano 2019, 13, 4640 -4646.

AMA Style

Minje Kim, Daehoon Park, Mehebub Alam, Sol Lee, Pangun Park, Junghyo Nah. Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS2 Composites. ACS Nano. 2019; 13 (4):4640-4646.

Chicago/Turabian Style

Minje Kim; Daehoon Park; Mehebub Alam; Sol Lee; Pangun Park; Junghyo Nah. 2019. "Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS2 Composites." ACS Nano 13, no. 4: 4640-4646.

Journal article
Published: 01 March 2019 in Applied Physics Express
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ACS Style

Hyunjoon Park; Junkyu Han; David C. Dillen; Joonsuk Park; Changho Kim; Minhyung Sim; Junghyo Nah; Jongwoo Lim; Emanuel Tutuc; Jae Hun Seol. Thermal conductivity measurement and analysis of Ge-Si x Ge1−x core–shell nanowires. Applied Physics Express 2019, 12, 045001 .

AMA Style

Hyunjoon Park, Junkyu Han, David C. Dillen, Joonsuk Park, Changho Kim, Minhyung Sim, Junghyo Nah, Jongwoo Lim, Emanuel Tutuc, Jae Hun Seol. Thermal conductivity measurement and analysis of Ge-Si x Ge1−x core–shell nanowires. Applied Physics Express. 2019; 12 (4):045001.

Chicago/Turabian Style

Hyunjoon Park; Junkyu Han; David C. Dillen; Joonsuk Park; Changho Kim; Minhyung Sim; Junghyo Nah; Jongwoo Lim; Emanuel Tutuc; Jae Hun Seol. 2019. "Thermal conductivity measurement and analysis of Ge-Si x Ge1−x core–shell nanowires." Applied Physics Express 12, no. 4: 045001.

Journal article
Published: 28 February 2019 in Scientific Reports
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The thermal conductivity enhancement of neat poly(vinyl alcohol) and poly(vinyl alcohol) (PVA)/cellulose nanocrystal (CNC) composite was attempted via electrospinning. The suspended microdevice technique was applied to measure the thermal conductivity of electrospun nanofibers (NFs). Neat PVA NFs and PVA/CNC NFs with a diameter of approximately 200 nm showed thermal conductivities of 1.23 and 0.74 W/m-K, respectively, at room temperature, which are higher than that of bulk PVA by factors of 6 and 3.5, respectively. Material characterization by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis confirmed that the thermal conductivity of the PVA/CNC NFs was enhanced by the reinforcement of their backbone rigidity, while that of the neat PVA NFs was attributed to the increase in their crystallinity that occurred during the electrospinning.

ACS Style

Yeongcheol Park; Myungil You; Jihoon Shin; Sumin Ha; Dukeun Kim; Min Haeng Heo; Junghyo Nah; Yoong Ahm Kim; Jae Hun Seol. Thermal conductivity enhancement in electrospun poly(vinyl alcohol) and poly(vinyl alcohol)/cellulose nanocrystal composite nanofibers. Scientific Reports 2019, 9, 1 -10.

AMA Style

Yeongcheol Park, Myungil You, Jihoon Shin, Sumin Ha, Dukeun Kim, Min Haeng Heo, Junghyo Nah, Yoong Ahm Kim, Jae Hun Seol. Thermal conductivity enhancement in electrospun poly(vinyl alcohol) and poly(vinyl alcohol)/cellulose nanocrystal composite nanofibers. Scientific Reports. 2019; 9 (1):1-10.

Chicago/Turabian Style

Yeongcheol Park; Myungil You; Jihoon Shin; Sumin Ha; Dukeun Kim; Min Haeng Heo; Junghyo Nah; Yoong Ahm Kim; Jae Hun Seol. 2019. "Thermal conductivity enhancement in electrospun poly(vinyl alcohol) and poly(vinyl alcohol)/cellulose nanocrystal composite nanofibers." Scientific Reports 9, no. 1: 1-10.