41 results on '"SangGap Lee"'
Search Results
2. Field Mapping of the Jointless HTS Solenoid Magnet in a Persistent Current Mode Operation
- Author
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Woo-Seok Kim, Ji-Kwang Lee, Jun Hee Han, Gye-Won Hong, Kyeongdal Choi, Seyeon Lee, Sang Ho Park, Seungyong Hahn, SangGap Lee, and Miyeon Yoon
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Superconductivity ,Materials science ,Field (physics) ,business.industry ,Electrical engineering ,Mode (statistics) ,Persistent current ,Solenoid ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Conductor ,Electromagnetic coil ,Magnet ,Electrical and Electronic Engineering ,business - Abstract
In order to achieve a persistent current mode operation with high-temperature superconducting (HTS) coils, we have been trying to improve the concept of a jointless HTS coil. The coil has a perfect closed loop without any joints in a coil, and we have proven that a persistent current can be induced in the coil by several charge up methods such as PCS, flux pump, or field cooling with a background magnet. In this paper, based on the previous experiment, which showed partially successful results [10], we designed and fabricated a small solenoid type jointless HTS magnet with a 100-m-long ReBCO wide conductor and tested it in a liquid nitrogen bath. After the persistent current mode operation of 15 h, we tried to measure temporal and spatial homogeneity by a field mapper we developed under the DSV of 10 mm .
- Published
- 2019
3. Field Measurement and Analysis of a 3 T 66 mm No-Insulation HTS NMR Magnet With Screening Current and Manufacturing Uncertainty Considered
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Jeseok Bang, SangGap Lee, Min Cheol Ahn, Jaemin Kim, Young Jin Hwang, Jae Young Jang, Jung Tae Lee, Mincheol Cho, Seungyong Hahn, and Seokho Kim
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Superconductivity ,Nmr magnet ,Materials science ,Full field ,Condensed Matter Physics ,01 natural sciences ,Homogenization (chemistry) ,Electronic, Optical and Magnetic Materials ,Computational physics ,Magnetic field ,Electromagnetic coil ,Magnet ,0103 physical sciences ,Electrical and Electronic Engineering ,010306 general physics - Abstract
This paper reports calculation and measurement of magnetic fields from a 3 T 66-mm room-temperature bore no-insulation high-temperature superconductor nuclear magnetic resonance (NMR) magnet with screening current and manufacturing uncertainty considered. The magnet reached its full field, 3 T under a conduction-cooling environment at 17 K. The measured magnetic fields along the magnet axis showed a substantial discrepancy to the originally designed ones. In simulation, measured dimensions of the 66 total single pancake coils of the magnet were used in consideration of the manufacturing errors of each pancake coil. And, the two-dimensional edge-element method with the domain homogenization technique was adopted to simulate screening currents within pancake coils and calculate the consequent screening current induced fields. The normalized magnetic fields between simulation and measurement showed good agreement that implies a potential to calculate “actual” magnetic fields of an REBCO NMR magnet with our approach.
- Published
- 2019
4. Development of a Cryogen-Free High-Temperature Superconducting Magnet for Use in Nuclear Magnetic Resonance
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Jaemin Kim, Yong-Ju Hong, Jae Young Jang, Hankil Yeom, Jeseok Bang, Seungyong Hahn, Young Jin Hwang, Hunju Lee, SangGap Lee, Mincheol Ahn, and Sehwan In
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Materials science ,Condensed matter physics ,Magnet ,High temperature superconducting - Published
- 2019
5. A High-Resolution Magnetometer Over a Wide Homogeneity Range
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Seungyong Hahn, Jun Hee Han, Min Cheol Ahn, Jae Young Jang, Changsoo Kim, Young Jin Hwang, and SangGap Lee
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010302 applied physics ,Materials science ,Magnetometer ,business.industry ,Field homogeneity ,Superconducting magnet ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetic field ,Optics ,law ,Magnet ,0103 physical sciences ,Homogeneity (physics) ,Electrical and Electronic Engineering ,010306 general physics ,business - Abstract
In this study, we introduce a highly accurate NMR magnetometer, which is capable of measuring the magnetic field for inhomogeneous HTS magnets. The magnetometer is based on the pulsed and Fourier-transformed NMR and 1H NMR signal analyses. The magnetometer system was fabricated according to these concepts and magnetic field measurements on a 3 T HTS magnet were carried out using various mapping paths. The test results demonstrate that the magnetometer can measure magnetic fields accurately in inhomogeneous conditions as high as approximately 864 ppm with a spherical volume of 10 mm in diameter nearly centered at the magnet center. The stronger and hence shorter RF pulse resulting from the high-power amplification enables measurements of magnetic fields in more inhomogeneous conditions. Because the permissible field homogeneity range is very wide, the magnetometer can be used for mapping fields at the preshim stage of the inhomogeneous magnets. To also verify the high-resolution performance of the magnetometer, the results are compared with measurement data obtained with a Hall magnetometer ordinarily used in such an inhomogeneity range. We expect that the proposed magnetometer will enable the precise measurements of the magnetic fields over a wide homogeneity range, and thereby bring about improvement in the shimming process of the inhomogeneous magnets.
- Published
- 2018
6. Characteristic Analysis of an HTS Flux-Switching Synchronous Generator With NI-Type HTS Field Coils
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SangGap Lee, Jae Young Jang, Jong Myung Kim, and Young Jin Hwang
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010302 applied physics ,Materials science ,business.industry ,Stator ,Electrical engineering ,Permanent magnet synchronous generator ,Condensed Matter Physics ,01 natural sciences ,Field coil ,Electronic, Optical and Magnetic Materials ,Overcurrent ,law.invention ,Magnetic core ,law ,Electromagnetic coil ,0103 physical sciences ,Electrical and Electronic Engineering ,010306 general physics ,business ,Excitation ,Armature (electrical engineering) - Abstract
This paper presents the characteristics analysis of the flux-switching synchronous generator (FSG) applying no-insulation (NI)-type high-temperature superconducting (HTS) field coils. The HTS FSG can be cost effective, since the field coils and armature windings are both installed in the stator, while the rotor is only made of iron core with tooth. Along with low cost, since HTS field coils in the FSGs are located in the stationary part of the generator, FSG can be a solution for the design complexities of the excitation and cooling systems for HTS field coils. In addition, several studies on HTS coils without turn-to-turn insulation (NI) have been reported for HTS field coils for applying in electrical rotating machines. The NI-type winding technique enhances the stability of the HTS field coil since the overcurrent is automatically bypassed through the contacts between winding turns. Nevertheless, there is still an issue about whether the NI-type HTS field coil can be applied to the electrical rotating machines. In this study, we fabricated and tested an NI-type HTS field coil. In addition, a 600-kW HTS FSG was designed using a fundamental design process and the characteristics analysis of the generator was performed based on the test results of the fabricated NI-type field coil. The results show that the HTS FSG having NI-type HTS field coils is able to operate normally under normal operating conditions. However, the field current charging problem issue has been revealed through this study. Therefore, further research will need to improve the problem.
- Published
- 2018
7. Optimal Design Methodology of Multiwidth HTS Magnet for Minimum Wire Consumption
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Min Cheol Ahn, Jae Young Jang, Hongmin Yang, Seungyong Hahn, SangGap Lee, and Kyungmin Kim
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Optimal design ,High-temperature superconductivity ,Materials science ,Mechanical engineering ,Field strength ,02 engineering and technology ,Superconducting magnet ,Integrated circuit ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,Magnet ,0103 physical sciences ,Stored energy ,Electrical and Electronic Engineering ,Control sample ,010306 general physics ,0210 nano-technology - Abstract
This paper investigates an optimal design methodology for multiwidth (MW) high-temperature superconductor (HTS) magnets, where pancake coils wound with the narrowest tapes were placed at and near the magnet center and those with progressively wider tapes toward the top and bottom of the magnet. For a given design, target of field strength and winding bore, input parameters include tape width, number of grading tapes, and number of pancakes coils, while the main objective is to minimize the magnet volume, i.e., essentially the stored energy and thus the cost. A magnet with a single-width tape is also designed as a control sample for comparison. A case study on a design of 3-T 240-mm HTS magnet was carried out. In that case, MW magnets save 40% wire consumption of single-width magnets. The results are expected to be beneficial to determine the practical level of HTS tape grading and estimate a volume of an MW magnet.
- Published
- 2018
8. Experimental study of the effect of the current sweep cycle on the magnetic field stability of a REBCO coil
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Young Jin Hwang, SangGap Lee, Woo Seung Lee, Jiho Lee, and Jae Young Jang
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010302 applied physics ,Materials science ,Field (physics) ,Condensed matter physics ,General Physics and Astronomy ,01 natural sciences ,Stability (probability) ,Magnetic field ,Nuclear magnetic resonance ,Homogeneous ,Electromagnetic coil ,0103 physical sciences ,General Materials Science ,Current (fluid) ,010306 general physics - Abstract
This paper reports the effects of a current sweep cycle method on reducing the screening current induced field (SCF) in a (RE)Ba2Cu3Ox (REBCO) coil. The screening current induced field in a REBCO coil causes two major problems: temporal magnetic field drift and a reduction of the central magnetic field. This is a critical problem in relation to REBCO coils, which require a homogeneous and stable magnetic field, during, for instance, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications (Itoh et al., 2013; Hemmi et al., 2005; Hahn et al., 2008; Amemiya et al., 2008; Otsuka et al., 2011; Yang et al., 2013; Ahn et al., 2009; Koyama et al., 2009; Kajikawa et al., 2015). In an effort to circumvent the SCF problem, the current sweep cycle method is investigated based on experiments in this study. The experimental results show that a greater SCF reduction in a REBCO coil can be obtained by increasing the overshooting of the current sweep cycle.
- Published
- 2018
9. Continuously thermal conductive pathway of bidisperse boron nitride fillers in epoxy composite for highly efficient heat dissipation
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Sooyeol Jeong, Lee Su Kim, Sung-Jin Chang, Jung Young Cho, Gi-Ra Yi, Gaehang Lee, Kyuseok Choi, Sun Ha Kim, Myungsu Kim, Joon Yong Park, Jun Min Kim, Ki Min Nam, Dae-Woong Jung, and SangGap Lee
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Materials science ,Composite number ,02 engineering and technology ,Epoxy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Mechanics of Materials ,Boron nitride ,visual_art ,Thermal ,Materials Chemistry ,visual_art.visual_art_medium ,Surface modification ,General Materials Science ,Composite material ,0210 nano-technology ,Electrical conductor ,Benzoic acid - Abstract
This study presents a combined strategy of bidisperse boron nitride (BN) and surface modification to improve the thermal conductivity (κ) of the BN-epoxy composite. Surface modification of hexagonal BN was carried out with benzoic acid (BA). The optimal weight ratio of large and small BN (BNl and BNs) was 8:2 for their connectivity in the epoxy matrix. For 50 wt% filler content, the BNl8s2-BA composite has a much higher κ of 2.71 W/m K (out-plane direction), which is 12.3, 1.32, and 1.50 times higher than that of the pure epoxy, and its composite with BNl10s0-BA and BNl8s2, respectively. The chemical-sensitive analyses indicate that carboxyl-carboxylate interaction occurred in partially deprotonated benzoic acid on BN during the epoxy curing process, resulting in in-situ formation of a continuously thermal conductive pathway, which is responsible for the improved κ.
- Published
- 2021
10. Three-Dimensional Numerical Simulation Employing Normal Zone Propagation Velocity on Heat Propagation of LTS Magnet Under Quench Process
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Young Jin Hwang, Min Cheol Ahn, Jae Young Jang, Sangjin Lee, Jinsub Kim, and SangGap Lee
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Physics ,Normal zone ,Condensed matter physics ,Computer simulation ,Magnet ,0103 physical sciences ,Process (computing) ,Mechanics ,Electrical and Electronic Engineering ,010306 general physics ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials - Published
- 2017
11. A Study on Mitigation of Screening Current Induced Field with a 3-T 100-mm Conduction-Cooled Metallic Cladding REBCO Magnet
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Seungyong Hahn, Young Jin Hwang, Jaemin Kim, SangGap Lee, Sangwon Yoon, Jun Hee Han, Min Cheol Ahn, Jae Young Jang, Kyungmin Kim, Hunju Lee, and Hankil Yeom
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010302 applied physics ,Materials science ,Field (physics) ,Magnetometer ,Superconducting magnet ,Condensed Matter Physics ,Thermal conduction ,Cladding (fiber optics) ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetic field ,Nuclear magnetic resonance ,Stack (abstract data type) ,law ,Magnet ,0103 physical sciences ,Electrical and Electronic Engineering ,Composite material ,010306 general physics - Abstract
A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1–2 $\mu {\text{m}}$ stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet
- Published
- 2017
12. Quench Analysis of a Multiwidth No-Insulation 7-T 78-mm REBCO Magnet
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Kwanglok Kim, Seungyong Hahn, Kabindra R. Bhattarai, Seokho Kim, and SangGap Lee
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010302 applied physics ,Materials science ,Computation ,Mechanical engineering ,Condensed Matter Physics ,Inductor ,01 natural sciences ,Inductive coupling ,Electronic, Optical and Magnetic Materials ,law.invention ,Nuclear magnetic resonance ,law ,Electromagnetic coil ,Magnet ,0103 physical sciences ,Transient (oscillation) ,Electrical and Electronic Engineering ,Resistor ,010306 general physics ,Voltage - Abstract
Due to the self-protecting feature, no-insulation (NI) high-temperature superconductor magnets have been regarded as a reliable option to generate high fields, yet their intrinsic charging delay still remains a major drawback. To apply the NI technique for actual high-field user magnets, however, postquench transient behavior of such magnets need to be fully understood, particularly the electromagnetic interaction among magnetically coupled subcoils. Recent publications have shown successful simulations of the transient behavior of a single NI coil or a multicoil magnet using distributed network models. Even though these approaches are very accurate, they often require substantial computation time, especially when multiple iterations are required during design or analysis of an NI magnet having a large number of coils. This paper presents a simple circuit approach that may be effective for quench simulation of multicoil NI magnets. Each NI subcoil in a magnet is lumped into a single inductor with a resistor in series and a resistor in parallel. This approach has allowed us to simulate the whole magnet system within reasonable time without compromising the understanding of mutual interactions of all of the subcoils after quench, namely change in parameters such as voltage, current, and temperature with respect to time and coil to coil normal zone propagation in an electromagnetic manner. We verified the proposed approach by analyzing the quench process in a previously built 7 T, 78 mm all-REBCO NI magnet (by MIT), and by doing the first ever comparison between the simulated results with the data measured from actual experiment.
- Published
- 2017
13. Feasibility Study of the Impregnation of a No-Insulation HTS Coil Using an Electrically Conductive Epoxy
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Seunghyun Song, Jong Myung Kim, SangGap Lee, Jae Young Jang, and Young Jin Hwang
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010302 applied physics ,Superconductivity ,High-temperature superconductivity ,Materials science ,Rotor (electric) ,Epoxy ,Condensed Matter Physics ,01 natural sciences ,Field coil ,Electronic, Optical and Magnetic Materials ,Magnetic field ,law.invention ,Electromagnetic coil ,law ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,Thermal stability ,Electrical and Electronic Engineering ,Composite material ,010306 general physics - Abstract
This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1] , [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines.
- Published
- 2017
14. 400-MHz/60-mm All-REBCO Nuclear Magnetic Resonance Magnet: Magnet Design
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Jaemin Kim, Hunju Lee, Seungyong Hahn, Kyekun Cheon, Kwang Lok Kim, SangGap Lee, Dong Lak Kim, and Sangwon Yoon
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010302 applied physics ,Materials science ,Superconducting magnetic energy storage ,Superconducting magnet ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Nuclear magnetic resonance ,Stack (abstract data type) ,Magnet ,0103 physical sciences ,Perpendicular ,User Facility ,Electrical and Electronic Engineering ,010306 general physics ,Conduction cooling - Abstract
We present a design of a 400-MHz/60-mm all-REBCO nuclear magnetic resonance (NMR) magnet (H400) that consists of a stack of 56 double-pancake (DP) coils. With the multiwidth no-insulation technique incorporated, DP coils were wound with REBCO tapes of five different widths, i.e., 4.1, 5.1, 6.1, 7.1, and 8.1 mm; DP coils placed at and near the magnet midplane were wound with the narrowest (4.1 mm wide) REBCO tapes, whereas those with progressively wider tapes were placed toward the top and bottom of the magnet, where the “perpendicular field B ⊥ ” is at its peak within the magnet. The magnet was designed to be operated under a conduction cooling environment at 20 K. Once successfully completed, the magnet will be installed as an NMR user facility in the Korea Basic Science Institute. Basic magnet performances and major technical challenges were discussed.
- Published
- 2016
15. Effect of Resistive Metal Cladding of HTS Tape on the Characteristic of No-Insulation Coil
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Kang Hwan Shin, Seungyoung Hahn, Hunju Lee, Seung-Hyun Moon, Sangwon Yoon, Kyekun Cheon, Dong Lak Kim, Jaemin Kim, and SangGap Lee
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010302 applied physics ,Superconductivity ,Resistive touchscreen ,Materials science ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Holding current ,Electromagnetic coil ,0103 physical sciences ,Equivalent circuit ,Electrical and Electronic Engineering ,Current (fluid) ,Composite material ,010306 general physics ,Electroplating ,Layer (electronics) - Abstract
This paper presents experimental and theoretical studies of the no-insulation (NI) winding method of second-generation high-temperature superconducting (HTS) wire. We compared two single pancake coils wound by two different HTS wires. One pancake coil is made of a normal HTS wire with an electroplated copper stabilizer. The other pancake coil is made of the same HTS wire with the only difference in an additional outermost layer made of stainless steel. We employed an equivalent circuit model to evaluate our experimental results. We tested both coils by the same simple operating procedure consisting of two steps: first, ramping up of current from zero to holding current (IH) and second, keeping the IH at minimum 500 s. We also tested the stability of the coil wound by an HTS wire with an additional layer of stainless steel by applying a current exceeding a critical current of the coil. We observed a charging time of the metal-cladding HTS coil reduced to a quarter of copper-electroplated HTS coil.
- Published
- 2016
16. Sustainable Method for the Large-Scale Preparation of Fe3 O4 Nanocrystals
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Jaesik Yoon, Sungkyoung Kang, SungWoo Lee, SangGap Lee, Gaehang Lee, Jong-Ryul Jeong, Ki Soo Chang, Kihyun Kwon, Ki Min Nam, and Sang-Il Choi
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Materials science ,Thermal decomposition ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Nanomaterials ,Solvent ,Chemical engineering ,Nanocrystal ,law ,Transmission electron microscopy ,Materials Chemistry ,Ceramics and Composites ,Crystallization ,0210 nano-technology ,Spectroscopy ,Porosity - Abstract
In this work, a facile synthetic process is reported for the large-scale synthesis of Fe3O4 nanocrystals. Thermal decomposition of Fe(acac)3 (100 g) in 1-hexadecanol produced Fe3O4 nanocrystals with well-controlled sizes and morphologies. The nanocrystals were spherically shaped with average diameters of 7.8 ± 0.6, 6.5 ± 0.4, and 5.9 ± 0.2 nm when prepared at 300°C, 270°C, and 250°C, respectively. Mechanisms of crystal formation were elucidated on the basis of gas chromatography-mass spectroscopy analysis, enabling the large-scale preparation of Fe3O4 nanocrystals. To provide an environmentally benign route, Fe3O4 nanocrystals were prepared with recycled solvent which was recovered from the initial experiment. The resulting porous Fe3O4 nanocrystals had larger average sizes than those of the initial nanocrystals. Structural characterization was performed using transmission electron microscopy and powder X-ray diffraction.
- Published
- 2016
17. A Flux-Controllable NI HTS Flux-Switching Machine for Electric Vehicle Applications
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SangGap Lee, Jae Young Jang, and Young Jin Hwang
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Electric motor ,Materials science ,business.product_category ,Field (physics) ,Flux ,Topology (electrical circuits) ,lcsh:Technology ,01 natural sciences ,lcsh:Chemistry ,flux regulation ,0103 physical sciences ,Electric vehicle ,General Materials Science ,010306 general physics ,Operational stability ,lcsh:QH301-705.5 ,Instrumentation ,010302 applied physics ,Fluid Flow and Transfer Processes ,lcsh:T ,business.industry ,Process Chemistry and Technology ,electric vehicle ,General Engineering ,Electrical engineering ,Field coil ,lcsh:QC1-999 ,Computer Science Applications ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,Electromagnetic coil ,flux-switching machine ,no-insulation ,HTS ,lcsh:Engineering (General). Civil engineering (General) ,business ,lcsh:Physics - Abstract
This paper deals with a flux-controllable NI HTS flux-switching machine (FSM) for electric vehicle (EV) applications. In a variable-speed rotating machine for EVs, such as electric buses, electric aircraft and electric ships, an electric motor capable of regulating the flux offers the advantage of constant output operation. In general, conventional HTS rotating machines have excellent flux-regulation performance, because they excite an HTS field coil. However, it is difficult to ensure any flux-regulation capabilities in HTS rotating machines using HTS field coils that apply the no-insulation (NI) winding technique, due to the inherent charge and discharge delays in these machines. Nevertheless, the NI winding technique is being actively researched as a key technology for the successful development of HTS rotating machines, because it can dramatically improve the operational stability of HTS field coils. Therefore, research to implement an HTS rotating machine with flux-regulation capabilities, while improving the operating stability of the HTS field coil using the NI winding technique, is required for EV applications. In this paper, we propose an HTS rotating machine with a flux switching structure, a type of topology of a rotating machine that is being actively studied for application to the electric motors used in EVs. The proposed HTS flux-switching machine (FSM) uses NI field coils, but additional field windings are applied for flux regulation, which enables flux control. In this study, an NI HTS field coil was also fabricated and tested because the characteristic resistance value should be used for the design and characteristic analyses of machines which utilize an NI coil. The simulation model used to analyze the flux-regulation performance capabilities of the NI HTS FSM were devised based on the characteristic resistance values obtained from a charging test of the fabricated NI HTS field coil. This study can provide a good reference for further research, including work on the manufacturing of a prototype NI HTS FSM for EV applications, and it can be used as a reference for the development of other HTS rotating machines, such as those used in large-scale wind power generation, where flux-regulation capabilities are required.
- Published
- 2020
18. Understanding quench in no-insulation (NI) REBCO magnets through experiments and simulations
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T.A. Painter, Kabindra R. Bhattarai, Iain R. Dixon, Kwangmin Kim, Xinbo Hu, Kyle Radcliff, Chaemin Im, SangGap Lee, David C. Larbalestier, Kwanglok Kim, and Seungyong Hahn
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010302 applied physics ,Copper oxide ,Materials science ,Nuclear engineering ,Contact resistance ,Rare earth ,Metals and Alloys ,Condensed Matter Physics ,Inductor ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Hall effect ,Electromagnetic coil ,Magnet ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Electrical and Electronic Engineering ,010306 general physics ,Voltage - Abstract
Present researches on no-insulation (NI) rare earth barium copper oxide (REBCO) magnets have demonstrated their ability to produce high fields due to their compact nature. NI magnets have often been demonstrated to be self-protecting. However, evidence of mechanical damage in recent high field magnets, is suggesting some issues about quench that must be resolved for this otherwise promising technology. This article attempts to explain multi-physics phenomena occurring during the quench of an NI magnet that can be used to elucidate quench behavior through experiments and simulations. A lumped circuit model is used for the circuit analysis here each coil is modeled as a single inductor with variable quench resistance in series and characteristic contact resistance in parallel. Three case studies have been analyzed: (1) a 3 double pancake (DP) standalone magnet, (2) a 2 DP coil in 31 T background, and (3) an HTS/LTS hybrid user magnet that consists of a 13 T HTS insert and a 6 T LTS background magnet. Lessons learned from these analyses include: (1) characteristic resistance of NI coil rises during quench with the temperature rise; (2) influence of Hall effect exists on the voltage rise during quench; (3) over-current during quench can over-stress the coil; and (4) quench propagation from one end of the magnet generates significant unbalanced forces. This approach is expected to be used in the preliminary design of an ultra high field (>40 T) user magnet currently under design in National High Magnetic Field Laboratory.
- Published
- 2020
19. Reproducibility of the field homogeneity of a metal-clad no-insulation all-REBCO magnet with a multi-layer ferromagnetic shim
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Jeseok Bang, Min Cheol Ahn, Jae Young Jang, Seungyong Hahn, Jun Hee Han, SangGap Lee, Hongmin Yang, and Young Jin Hwang
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Reproducibility ,Materials science ,Ferromagnetism ,Magnet ,Field homogeneity ,Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,Shim (magnetism) ,Electrical and Electronic Engineering ,Composite material ,Condensed Matter Physics ,Multi layer - Published
- 2020
20. Efficient visible-light responsive TiO2 nanoparticles incorporated magnetic carbon photocatalysts
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Doo Ri Bae, Sang Moon Lee, Changsoo Kim, Gaehang Lee, Hyun Uk Lee, Byoungchul Son, Young-Chul Lee, Jae-Won Lee, Ji Chan Park, Soon Chang Lee, SangGap Lee, Bora Nam, Jouhahn Lee, So Young Park, and Jaesik Yoon
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Anatase ,Chemistry ,General Chemical Engineering ,Iron oxide ,Nanoparticle ,Nanotechnology ,General Chemistry ,Sterilization (microbiology) ,Industrial and Manufacturing Engineering ,Catalysis ,chemistry.chemical_compound ,Photocatalysis ,medicine ,Environmental Chemistry ,Nuclear chemistry ,Activated carbon ,medicine.drug ,Visible spectrum - Abstract
We developed a photocatalyst (T–FC) that incorporated anatase TiO2 (T) nanoparticles on magnetically enhanced carbon [iron oxide (F; α,γ-Fe2O3–Fe3O4) supported on activated carbon (C)] for use as a highly visible-light-active, low-cost, recyclable, and photostable catalyst for the degradation of organic dyes and bacterial sterilization. The T–FC photocatalyst with a large Brunauer–Emmett–Teller surface area (564.3 m2 g−1) was synthesized by wet-chemical processing and ultrasound irradiation. Under visible-light irradiation, the highest photocatalytic activity for T–FC ([k] = 3.874 h−1) was 32.6 and 3.1 times higher than those of T ([k] = 0.119 h−1) and FC ([k] = 1.259 h−1). The recyclability of T–FC was high, with a dye decolorization rate measured at ∼95.8% of the initial value after 15 recycles. Furthermore, T–FC showed more substantial antimicrobial properties against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) than T and FC when exposed to visible-light for 120 min. Even after 10 cycles of use, T–FC killed more than 95.7% of E. coli. These results indicated that T–FC might have utility in several promising applications such as wastewater treatment and as a bactericidal agent.
- Published
- 2014
21. Efficient dynamic nuclear polarization of phosphorus in silicon in strong magnetic fields and at low temperatures
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Jarno Järvinen, O. Vainio, L. Lehtonen, Soonchil Lee, S. Sheludyakov, Yutaka Fujii, SangGap Lee, J. Ahokas, Leonid S. Vlasenko, M. Gwak, Sergey Vasiliev, Seitaro Mitsudo, Takao Mizusaki, and D. Zvezdov
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Physics ,Silicon ,Spins ,ta114 ,Relaxation (NMR) ,ta1182 ,chemistry.chemical_element ,Condensed Matter Physics ,Polarization (waves) ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetic field ,Nuclear magnetic resonance ,chemistry ,law ,Impurity ,Qubit ,Atomic physics ,Electron paramagnetic resonance ,ta116 - Abstract
Efficient manipulation of nuclear spins is important for utilizing them as qubits for quantum computing. In this work we report record high polarizations of ${}^{31}\mathrm{P}$ and $^{29}\mathrm{Si}$ nuclear spins in P-doped silicon in a strong magnetic field (4.6 T) and at temperatures below 1 K. We reached ${}^{31}\mathrm{P}$ nuclear polarization values exceeding $98%$ after 20 min of pumping the high-field electron spin resonance (ESR) line with a very small microwave power of 0.4 $\ensuremath{\mu}\mathrm{W}$. We evaluate that the ratio of the hyperfine-state populations increases by three orders of magnitude after 2 hours of pumping, and an extremely pure nuclear spin state can be created, with less than 0.01 ppb impurities. A negative dynamic nuclear polarization has been observed by pumping the low-field ESR line of ${}^{31}\mathrm{P}$ followed by the flip-flip cross relaxation, the transition which is fully forbidden for isolated donors. We estimate that while pumping the ESR transitions of ${}^{31}\mathrm{P}$ also the nuclei of $^{29}\mathrm{Si}$ get polarized, and polarization exceeding $60%$ has been obtained. We performed measurements of relaxation rates of flip-flop and flip-flip transitions which turned out to be nearly temperature independent. Temperature dependence of the ${}^{31}\mathrm{P}$ nuclear relaxation was studied down to 0.75 K, below which the relaxation time became too long to be measured. We found that the polarization evolution under pumping and during relaxation deviates substantially from a simple exponential function of time. We suggest that the nonexponential polarization dynamics of ${}^{31}\mathrm{P}$ donors is mediated by the orientation of $^{29}\mathrm{Si}$ nuclei, which affect the transition probabilities of the forbidden cross-relaxation processes.
- Published
- 2014
22. Study of ferroelectric–paraelectric phase transition of RbH2AsO4 single crystals by 87Rb NMR relaxation time measurements
- Author
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SangGap Lee, Kwang-Sei Lee, Ae Ran Lim, and Changsoo Kim
- Subjects
Phase transition ,Condensed matter physics ,Chemistry ,General Chemistry ,Dielectric ,Condensed Matter Physics ,Ferroelectricity ,Ion ,Condensed Matter::Materials Science ,Tetragonal crystal system ,Crystallography ,Phase (matter) ,Materials Chemistry ,Orthorhombic crystal system ,Line (formation) - Abstract
The temperature dependences of the resonance frequency, line width, and spin–lattice relaxation time T 1 of the ferroelectric and paraelectric phases of RbH 2 AsO 4 crystals are investigated. The 87 Rb NMR line at the phase transition temperature T C (=110 K) splits into two lines, which indicates the occurrence of phase transition from tetragonal to orthorhombic phase. In addition, T 1 for the 87 Rb nucleus undergoes remarkable changes near T C , which indicates drastic alterations of the spin dynamics at T C . At T C , changes occur in the resonance frequency and T 1 , which are related to variations in the symmetry of the environments of the 87 Rb ions.
- Published
- 2014
23. Sea-urchin-like iron oxide nanostructures for water treatment
- Author
-
Young Boo Lee, So Young Park, Hyun Uk Lee, Soon Chang Lee, Jae-Won Lee, Bora Nam, Stane Vrtnik, Sang Moon Lee, SangGap Lee, Young-Chul Lee, Changsoo Kim, and Jouhahn Lee
- Subjects
Environmental Engineering ,Materials science ,Health, Toxicology and Mutagenesis ,Inorganic chemistry ,Magnetic separation ,Iron oxide ,Crystallography, X-Ray ,Ferric Compounds ,Water Purification ,chemistry.chemical_compound ,Adsorption ,Microscopy, Electron, Transmission ,Metals, Heavy ,Environmental Chemistry ,Organic Chemicals ,Waste Management and Disposal ,Pollutant ,Aqueous solution ,Sorption ,Pollution ,Nanostructures ,Congo red ,chemistry ,Microscopy, Electron, Scanning ,Water treatment ,Water Pollutants, Chemical - Abstract
To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe2O3/Fe3O4 phase) nanostructures (called u-MFN) with large surface areas (94.1m(2) g(-1)) and strong magnetic properties (57.9 emu g(-1)) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g(-1)) and Cr(VI) (35.0 mg g(-1)) and the organic pollutant Congo red (109.2 mg g(-1)). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions.
- Published
- 2013
24. Microscopic control ofSi29nuclear spins near phosphorus donors in silicon
- Author
-
S. Sheludyakov, Takao Mizusaki, Yutaka Fujii, Jarno Järvinen, D. Zvezdov, Seitaro Mitsudo, Leonid S. Vlasenko, Sergey Vasiliev, M. Gwak, O. Vainio, Soonchil Lee, J. Ahokas, L. Lehtonen, and SangGap Lee
- Subjects
Physics ,Spins ,Silicon ,chemistry.chemical_element ,Nuclear Overhauser effect ,Weak interaction ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Magnetic field ,law.invention ,chemistry ,law ,Excited state ,Atomic physics ,Electron paramagnetic resonance ,Excitation - Abstract
We demonstrate an efficient control of $^{29}\mathrm{Si}$ nuclear spins for specific lattice sites near $^{31}\mathrm{P}$ donors in silicon at temperatures below 1 K and in a high magnetic field of 4.6 T. Excitation of the forbidden electron-nuclear transitions leads to a pattern of well-resolved holes and peaks in the electron spin resonance (ESR) lines of $^{31}\mathrm{P}$. The pattern originates from dynamic polarization (DNP) of the $^{29}\mathrm{Si}$ nuclear spins near the donors via the solid effect. DNP of $^{29}\mathrm{Si}$ is demonstrated also with the Overhauser effect where the allowed ESR transitions are excited. In this case mostly the remote $^{29}\mathrm{Si}$ nuclei having weak interaction with the donors are polarized, which results in a single hole and a sharp peak pair in the ESR spectrum. Our work shows that the solid effect can be used for initialization of $^{29}\mathrm{Si}$ nuclear spin qubits near the donors.
- Published
- 2015
25. Design, construction and 13 K conduction-cooled operation of a 3 T 100 mm stainless steel cladding all-REBCO magnet
- Author
-
Hankil Yeom, Kyekun Cheon, Kwanglok Kim, Kang Hwan Shin, Seung-Hyun Moon, Young Jin Hwang, Jaemin Kim, Sangwon Yoon, Jae Young Jang, Seungyong Hahn, Hunju Lee, Sehwan In, Yong-Ju Hong, and SangGap Lee
- Subjects
010302 applied physics ,Materials science ,Metals and Alloys ,Condensed Matter Physics ,Cladding (fiber optics) ,Thermal conduction ,01 natural sciences ,Stack (abstract data type) ,Operating temperature ,Electromagnetic coil ,Magnet ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,Current density ,Voltage - Abstract
A conduction-cooled 3 T 100 mm winding bore multi-width and no-insulation (NI) all-REBCO magnet was designed, constructed and tested at 13 K. The magnet consists of a stack of double pancake (DP) coils wound with, for the first time, REBCO tapes having a 1 μm thick layer of stainless steel, named 'metallic cladding', that surrounds the tapes in a hermetic way to substantially reduce the NI charging delay. After construction, the magnet was cooled down to the target operating temperature of 13 K using a two-stage pulse-tube cryo-cooler. During charging–discharging tests up to 200 A, magnetic center field, voltage of each DP coil, power supply current, and magnet temperature were monitored. The charging time constant of the magnet was measured to be about 10.1 s, 13 times smaller than that of its NI counterpart. The magnet experienced, due to an unexpected power supply trip, a sudden discharge at a peak coil current density of 353 A mm2, yet it survived without any degradation. The results demonstrated strong potential of the metallic cladding NI-REBCO magnet for significant charging-delay reduction and self-protecting operation.
- Published
- 2017
26. Low-noise magnetoencephalography system cooled by a continuously operating reliquefier
- Author
-
SangGap Lee, Kwon-Kyu Yu, Kyong-Woo Kim, Hyu-Sang Kwon, J. M. Kim, Minjung Kim, and Y. H. Lee
- Subjects
010302 applied physics ,Materials science ,medicine.diagnostic_test ,Liquid helium ,Acoustics ,Metals and Alloys ,Thermal contact ,White noise ,Magnetoencephalography ,Condensed Matter Physics ,01 natural sciences ,Signal ,law.invention ,law ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,medicine ,Tube (fluid conveyance) ,Electrical and Electronic Engineering ,010306 general physics ,Pulse tube refrigerator ,Noise (radio) - Abstract
We fabricated a low-noise magnetoencephalography (MEG) system based on a continuously operating reliquefier for cooling of low-temperature superconducting quantum interference device gradiometers. In order to reduce the vibration transmission, the gradiometers are mounted in the vacuum space of the helmet dewar with direct thermal contact with the liquid helium helmet. The reliquefier uses a 1.4 W pulse tube cryocooler with a remote motor, and a horizontal transfer tube with a downslope angle of 1°. The white noise of the system is 3.5 fTrms/√Hz (at 100 Hz). The vibration-induced peak at 1.4 Hz is 18 fTrms/√Hz averaged over the whole helmet array of 150 channels, which is the lowest among the reported values using reliquefier cooling and comparable to the noise peak cooled by conventional direct liquid helium cooling with axial gradiometers of the same baseline. The spontaneous brain activity signal showed nearly identical signal quality with the reliquefier turned on and off, and the reliquefier-based MEG system noise is well below the brain noise level.
- Published
- 2017
27. Design and performance estimation of a 35 T 40 mm no-insulation all-REBCO user magnet
- Author
-
Kwanglok Kim, Jae Young Jang, Seungyong Hahn, Kwangmin Kim, Sangwon Yoon, Young Jin Hwang, Kabindra R. Bhattarai, and SangGap Lee
- Subjects
010302 applied physics ,Materials science ,Liquid helium ,Contact resistance ,Metals and Alloys ,Time constant ,Condensed Matter Physics ,Cladding (fiber optics) ,01 natural sciences ,law.invention ,Inductance ,law ,Magnet ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Equivalent circuit ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,Joule heating - Abstract
This paper presents a design of a 35 T 40 mm winding diameter no-insulation standalone magnet that consists of a stack of 52 double pancake (DP) coils wound with multi-width REBCO tapes. The inner and outer diameters and height of the magnet are 40 mm, 221.6 mm, and 628 mm, respectively. It is designed to generate 35 T at an operating current (I op) of 179.8 A in a bath of liquid helium at 4.2 K. All the DP coils will be 'dry' wound without epoxy, making turns within the DP coils to be essentially 'self-supporting,' which is effective to reduce the magnetic stress. To reduce the magnet charging time constant, the so-called 'metallic cladding' REBCO tapes will be adopted, where a 1–2 μm thick stainless steel layer surrounds the tapes hermetically. With an average surface contact resistance (R ct) of 170 cm−2, experimentally obtained from a charging test of our recent 3 T 100 mm stainless steel cladding REBCO magnet, the charging time constant of the 35 T magnet was estimated to be 3.01 minutes, though the magnet will be energized substantially slower over a few hours to reduce ac loss and Joule heating from radial turn-to-turn leak currents. A preliminary post-quench analysis, based on our lumped equivalent circuit model, was performed; the total stored energy of 1.79 MJ (magnet inductance: 110.5 H) was expected to be discharged in approximately 1.28 seconds after a quench due to the fast electromagnetic quench propagation among the DP coils, while the peak hot spot temperature was estimated to rise to 94 K, acceptable for a safe quench of a REBCO magnet.
- Published
- 2017
28. Experimental study on a conduction cooling system for a HTS NMR magnet
- Author
-
Hankil Yeom, Young Jin Hwang, Hyo-Bong Kim, Seong-Je Park, Sangwon Yoon, Jae Young Jang, Yong-Ju Hong, Junseok Ko, Sehwan In, Kyekeun Cheon, and SangGap Lee
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Nuclear engineering ,Cryocooler ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Vibration ,Operating temperature ,Magnet ,0103 physical sciences ,Water cooling ,Vacuum chamber ,Electrical and Electronic Engineering ,010306 general physics - Abstract
A nuclear magnetic resonance (NMR) magnet composed of a high-temperature superconductor (HTS) is expected to contribute to a smaller size and a higher magnetic field (>1 GHz) of the NMR magnet due to its high critical current density under high magnetic field and better mechanical properties. The high operating temperature of HTS NMR magnets also makes conduction cooling by a cryocooler available. The conduction cooling system combined with a cryocooler is compact and user-friendly but has critical issues about the design of conduction cooling passages and the mechanical vibration. The small-scale HTS magnet with the conduction cooling system is fabricated and tested to check the issues and establish the design basis as a preliminary step for the development of a 400-MHz HTS NMR magnet. Thermal analysis for heat loads and thermal resistances at main joints is performed from the temperature distribution of the cooling system. The vibration levels at the crycooler and the vacuum chamber are discussed in comparison to the vibration criterion of NMR magnets. In addition, the design approach to the conduction cooling system for the HTS NMR magnet is discussed.
- Published
- 2017
29. A Unified Picture of Cantilever Frequency-Shift Measurements of Magnetic Resonance
- Author
-
Eric W. Moore, John A. Marohn, and SangGap Lee
- Subjects
Physics ,Cantilever ,Computer simulation ,Spins ,medicine.diagnostic_test ,Magnetic resonance force microscopy ,Frequency shift ,Nanotechnology ,Magnetic resonance imaging ,Condensed Matter Physics ,Article ,Electronic, Optical and Magnetic Materials ,Amplitude ,Quantum electrodynamics ,medicine ,Adiabatic process - Abstract
We report a unified framework describing all existing protocols for spin manipulation and signal creation in frequency-modulation magnetic resonance force microscopy using classical perturbation theory. The framework is well suited for studying the dependence of the frequency shift on the cantilever amplitude via numerical simulation. We demonstrate the formalism by recovering an exact result for a single spin signal and by simulating, for the first time as a function of cantilever amplitude, the frequency shift due to a volume of noninteracting spins inverted by an adiabatic rapid passage. We show that an optimal cantilever amplitude exists that maximizes the signal. Our findings suggest that understanding the amplitude dependence of the spin signal will be important for designing future high-sensitivity experiments.
- Published
- 2014
30. NMR Spectroscopy for Thin Films by Magnetic Resonance Force Microscopy
- Author
-
Soonho Won, SangGap Lee, Kiwoong Kim, Seung Bo Saun, Yunseok Han, and Soonchil Lee
- Subjects
Multidisciplinary ,Materials science ,Magnet ,Perpendicular ,Magnetic resonance force microscopy ,Vector field ,Fluorine-19 NMR ,Nuclear magnetic resonance spectroscopy ,Thin film ,Bioinformatics ,Adiabatic process ,Molecular physics ,Article - Abstract
Nuclear magnetic resonance (NMR) is a fundamental research tool that is widely used in many fields. Despite its powerful applications, unfortunately the low sensitivity of conventional NMR makes it difficult to study thin film or nano-sized samples. In this work, we report the first NMR spectrum obtained from general thin films by using magnetic resonance force microscopy (MRFM). To minimize the amount of imaging information inevitably mixed into the signal when a gradient field is used, we adopted a large magnet with a flat end with a diameter of 336 μm that generates a homogeneous field on the sample plane and a field gradient in a direction perpendicular to the plane. Cyclic adiabatic inversion was used in conjunction with periodic phase inversion of the frequency shift to maximize the SNR. In this way, we obtained the (19)F NMR spectrum for a 34 nm-thick CaF2 thin film.
- Published
- 2013
31. High performance of a solid-state flexible asymmetric supercapacitor based on graphene films
- Author
-
Won Hi Hong, Hyun-Wook Kang, Bong Gill Choi, Chan Pil Park, Hae Jin Kim, SangGap Lee, Yun Suk Huh, and Sung-Jin Chang
- Subjects
Supercapacitor ,Materials science ,Fabrication ,Graphene ,law ,Electrode ,General Materials Science ,Nanotechnology ,Electrolyte ,Capacitance ,Energy storage ,Separator (electricity) ,law.invention - Abstract
Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO(2)-IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol-H(2)SO(4) electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg(-1)) and power density (6.8 kW g(-1)), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g(-1) with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.
- Published
- 2012
32. Characterizing zeta potential of functional nanofibers in a microfluidic device
- Author
-
SangGap Lee, Margaret W. Frey, and Daehwan Cho
- Subjects
Materials science ,Microfluidics ,Polyacrylonitrile ,Analytical chemistry ,Buffer (optical fiber) ,Streaming current ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Biomaterials ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Nanofiber ,Electrode ,Zeta potential ,Surface charge - Abstract
The measurement of surface charge on nanofibers was achieved by characterizing zeta potential of the nanofibers via a newly developed device for streaming current measurement. Low flow rates were sufficient to generate detectable streaming currents in the absence of an externally applied voltage without damaging nanofiber samples. Zeta potential was calculated by using the Helmholtz-Smoluchowski equation and the measured streaming currents. Two acrylic plates were machined and assembled to form a microfluidic channel that is 150 μm high, 2.0mm wide, and 30 mm long. Two electrodes for the measurement of streaming currents were housed in the top plate. Two nanofibers of pure polyacrylonitrile (PAN) fibers and charged (TiO(2) incorporated) PAN fibers were prepared and characterized in the device. Monobasic sodium phosphate and dibasic sodium phosphate were used to prepare four different pH buffer solutions ranging from pH 5 to pH 8 in order to characterize the zeta potentials. The pure PAN nanofibers had negatively-charged surfaces regardless of pH. However, the zeta potentials of PAN/TiO(2) nanofibers changed from positive to negative at pH 6.5. The zeta potential measurements made on the nanofibers in this new microfluidic device matched with those of the powdered raw materials using a commercial Zetasizer.
- Published
- 2011
33. Batch-fabrication of cantilevered magnets on attonewton-sensitivity mechanical oscillators for scanned-probe nanoscale magnetic resonance imaging
- Author
-
SangGap Lee, Jonilyn G. Longenecker, Lee E. Harrell, John A. Marohn, Sarah J Wright, Steven A. Hickman, and Eric W. Moore
- Subjects
Silicon ,Cantilever ,Materials science ,Magnetometer ,Physics::Instrumentation and Detectors ,General Physics and Astronomy ,Magnetic resonance force microscopy ,Nanotechnology ,Spectroscopy, Electron Energy-Loss ,Article ,law.invention ,Magnetization ,Magnetics ,law ,Nickel ,General Materials Science ,Mechanical Phenomena ,business.industry ,General Engineering ,Electron Spin Resonance Spectroscopy ,Resonance ,Magnetic Resonance Imaging ,Computer Science::Other ,Microscopy, Electron ,Magnet ,Optoelectronics ,Feasibility Studies ,Nanorod ,Magnetic force microscope ,business - Abstract
We have batch-fabricated cantilevers with ~100 nm diameter nickel nanorod tips and force sensitivities of a few attonewtons at 4.2 kelvin. The magnetic nanorods were engineered to overhang the leading edge of the cantilever and, consequently, the cantilevers experience what we believe is the lowest surface noise ever achieved in a scanned probe experiment. Cantilever magnetometry indicated that the tips were well magnetized, with a ≤ 20 nm dead layer; the composition of the dead layer was studied by electron microscopy and electron energy loss spectroscopy. In what we believe is the first demonstration of scanned probe detection of electron-spin resonance from a batch fabricated tip, the cantilevers were used to observe electron-spin resonance from nitroxide spin labels in a film via force-gradient-induced shifts in cantilever resonance frequency. The magnetic field dependence of the magnetic resonance signal suggests a non-uniform tip magnetization at an applied field near 0.6 T.
- Published
- 2010
34. Scanned-probe detection of electron spin resonance from a nitroxide spin probe
- Author
-
Peter P. Borbat, Steven A. Hickman, Sarah J Wright, SangGap Lee, Eric W. Moore, Jack H. Freed, Lee E. Harrell, and John A. Marohn
- Subjects
Multidisciplinary ,Cantilever ,Magnetic Resonance Spectroscopy ,Spin polarization ,Molecular Structure ,Chemistry ,Electron Spin Resonance Spectroscopy ,Magnetic resonance force microscopy ,Equipment Design ,Zero field splitting ,Ferromagnetic resonance ,Molecular physics ,Biophysical Phenomena ,law.invention ,Computer Science::Other ,Spin probe ,Cyclic N-Oxides ,Nuclear magnetic resonance ,law ,Physical Sciences ,Spin echo ,Thermodynamics ,Spin Labels ,Electron paramagnetic resonance ,Microwaves - Abstract
We report an approach that extends the applicability of ultrasensitive force-gradient detection of magnetic resonance to samples with spin-lattice relaxation times ( T 1 ) as short as a single cantilever period. To demonstrate the generality of the approach, which relies on detecting either cantilever frequency or phase, we used it to detect electron spin resonance from a T 1 = 1 ms nitroxide spin probe in a thin film at 4.2 K and 0.6 T. By using a custom-fabricated cantilever with a 4 μ m -diameter nickel tip, we achieve a magnetic resonance sensitivity of 400 Bohr magnetons in a 1 Hz bandwidth. A theory is presented that quantitatively predicts both the lineshape and the magnitude of the observed cantilever frequency shift as a function of field and cantilever-sample separation. Good agreement was found between nitroxide T 1 's measured mechanically and inductively, indicating that the cantilever magnet is not an appreciable source of spin-lattice relaxation here. We suggest that the new approach has a number of advantages that make it well suited to push magnetic resonance detection and imaging of nitroxide spin labels in an individual macromolecule to single-spin sensitivity.
- Published
- 2009
35. Inductive Detection of Magnetostrictive Resonance
- Author
-
Jang-ik Park, Yongho Seo, I. Yu, and SangGap Lee
- Subjects
Chemistry ,business.industry ,Detector ,Metals and Alloys ,FOS: Physical sciences ,Magnetostriction ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Condensed Matter - Other Condensed Matter ,Transducer ,Nuclear magnetic resonance ,Optics ,Electromagnetic coil ,Ferrite (magnet) ,Ultrasonic sensor ,Electrical and Electronic Engineering ,business ,Instrumentation ,Radiofrequency coil ,Other Condensed Matter (cond-mat.other) - Abstract
We have developed an inductive method to detect the magnetostrictive resonance signal and applied it to an ultrasonic magnetostrictive transducer sample. Slab shaped ferrite samples are mounted in an RF coil and actuated by pulse modulated RF magnetic field. A DC magnetic field is also applied and the resonance signal from the sample is detected by the same coil after the RF field is turned off. The detector system is similar to a conventional pulse NMR system with quadrature detection. The detected signal is sensitive to the bias DC field strength and direction as well as the dimension of the sample., Comment: 4 pages 5 figures
- Published
- 2006
- Full Text
- View/download PDF
36. High-frequency ESR measurements and ESR/NMR double resonance experiments of lightly phosphorous-doped silicon
- Author
-
Akira Fukuda, K. Morimoto, Akira Matsubara, Yutaka Fujii, M. Gwak, Seitaro Mitsudo, Soonchil Lee, SangGap Lee, Tomohiro Ueno, and Takao Mizusaki
- Subjects
musculoskeletal diseases ,History ,Silicon ,Chemistry ,Doping ,Analytical chemistry ,chemistry.chemical_element ,Atmospheric temperature range ,Polarization (waves) ,Rf field ,Computer Science Applications ,Education ,Magnetic field ,Esr spectra ,Condensed Matter::Materials Science ,Nuclear magnetic resonance ,Condensed Matter::Strongly Correlated Electrons ,skin and connective tissue diseases - Abstract
We studied lightly doped Si:P with high-frequency (80-120 GHz) ESR and ESR/NMR double magnetic resonance techniques in the temperature range down to 1.4 K. We found dynamic nuclear polarization of 31P from steady-state ESR measurements with approximately 3.6 T. We derived the nuclear spin relaxation time, T1N, of 31P by analysing the time-evolution of ESR spectra utilizing the dynamic nuclear polarization effect. We derive temperature and magnetic field dependence of T1N and compare with experimental data. Furthermore, from our ESR measurements, we modulate the nuclear polarization of 31P by applying an RF field.
- Published
- 2014
37. NMR of hydrogen adsorbed on carbon nanotubes
- Author
-
SangGap Lee, Jongjin Lee, and I. Yu
- Subjects
Materials science ,Condensed matter physics ,Hydrogen ,Cryo-adsorption ,Carbon nanofiber ,Relaxation (NMR) ,Selective chemistry of single-walled nanotubes ,Spin–lattice relaxation ,chemistry.chemical_element ,Carbon nanotube ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Catalysis ,law.invention ,Condensed Matter::Materials Science ,chemistry ,law ,Physical chemistry ,Physics::Atomic Physics ,Electrical and Electronic Engineering - Abstract
Hydrogen gas is introduced to multi-walled carbon nanotubes and 1 H nuclear magnetic resonances are measured as the functions of hydrogen gas pressure and temperature. The resonance frequency is shifted in inverse proportion to temperature due to the super-paramagnetic Fe catalysts that remained in the nanotubes. By the differences in relaxation times, the signal from hydrogen adsorbed on carbon nanotubes is differentiated from that of gas phase hydrogen.
- Published
- 2003
38. Electrical Insulation Characteristics of PPLP as a HTS DC Cable Dielectric and GFRP as Insulating Material for Terminations
- Author
-
Haigun Lee, Hyun-Man Jang, Seunghoe Kim, SangGap Lee, Jae-Hyeong Choi, Woe-Yeon Kim, Yungil Kim, and K. L. Kim
- Subjects
Materials science ,Dielectric strength ,Glass fiber ,Cryogenics ,Dielectric ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Conductor ,law ,Condensed Matter::Superconductivity ,Arc flash ,Water cooling ,All-dielectric self-supporting cable ,Electrical and Electronic Engineering ,Composite material - Abstract
A high-temperature superconducting (HTS) DC cable system has attracted a great deal of interest from the view point of low loss, dense structure and large capacity compared to HTS AC cable system. It has a HTS cable and a termination. A HTS DC cable system consists of a conductor, cooling system and electrical insulation. To realize the HTS DC cable system, it is important to study not only high current capacity and low loss of conductor but also optimum electrical insulation at cryogenic temperature. The electrical insulation technology of HTS DC cable and termination must be solved for the long life, reliability and compact of cable. In this paper, we will discuss mainly on the electrical insulation characteristics and the insulation design of 220 kV class HTS DC cable. Voltage-time (V-t) characteristics of laminated polypropylene paper (PPLP) in LN2 were studied. Furthermore, the surface flashover characteristics of glass fiber reinforced plastic (GFRP) for termination insulators under DC and lightning impulse voltage were studied.
- Published
- 2012
39. Switching through intermediate states seen in a single nickel nanorod by cantilever magnetometry
- Author
-
SangGap Lee, Jonilyn G. Longenecker, John A. Marohn, Steven A. Hickman, and Eric W. Moore
- Subjects
Cantilever ,Materials science ,Physics::Instrumentation and Detectors ,business.industry ,Magnetometer ,General Physics and Astronomy ,chemistry.chemical_element ,Nanotechnology ,Dissipation ,Computer Science::Other ,Magnetic field ,law.invention ,Magnetism and Superconductivity ,Magnetization ,Nickel ,chemistry ,law ,Optoelectronics ,Nanorod ,business ,Nanoscopic scale - Abstract
In-plane to out-of-plane magnetization switching in a single nickel nanorod affixed to an attonewton-sensitivity cantilever was studied at cryogenic temperatures. We observe multiple sharp, simultaneous transitions in cantilever frequency, dissipation, and frequency jitter associated with magnetic switching through distinct intermediate states. These findings suggest a new route for detecting magnetic fields at the nanoscale.
- Published
- 2012
40. Evading surface and detector frequency noise in harmonic oscillator measurements of force gradients
- Author
-
SangGap Lee, Steven A. Hickman, Lee E. Harrell, John A. Marohn, and Eric W. Moore
- Subjects
Physics ,Physics and Astronomy (miscellaneous) ,business.industry ,Frequency drift ,Variable-frequency oscillator ,Interdisciplinary and General Physics ,Phase-locked loop ,Vackář oscillator ,Voltage-controlled oscillator ,Optics ,Quantum mechanics ,Phase noise ,Parametric oscillator ,business ,Harmonic oscillator - Abstract
We introduce and demonstrate a method of measuring small force gradients acting on a harmonic oscillator in which the force-gradient signal of interest is used to parametrically up-convert a forced oscillation below resonance into an amplitude signal at the oscillator’s resonance frequency. The approach, which we demonstrate in a mechanically detected electron spin resonance experiment, allows the force-gradient signal to evade detector frequency noise by converting a slowly modulated frequency signal into an amplitude signal.
- Published
- 2010
41. Resistance Switching in Electroformed Pt/FeO x/Pt Structures
- Author
-
C. Liu, Dong-Wook Kim, Sunae Seo, SangGap Lee, Seo Hyoung Chang, Suyong Chae, and Chang Uk Jung
- Subjects
Materials science ,Electroforming ,General Physics and Astronomy ,Nanotechnology - Published
- 2007
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