142 results on '"Kwang-Seok Yun"'
Search Results
2. Photonic synaptic transistors with new electron trapping layer for high performance and ultra-low power consumption
- Author
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Taewoo Kim and Kwang-Seok Yun
- Subjects
Medicine ,Science - Abstract
Abstract Photonic synaptic transistors are being investigated for their potential applications in neuromorphic computing and artificial vision systems. Recently, a method for establishing a synaptic effect by preventing the recombination of electron–hole pairs by forming an energy barrier with a double-layer consisting of a channel and a light absorption layer has shown effective results. We report a triple-layer device created by coating a novel electron-trapping layer between the light-absorption layer and the gate-insulating layer. Compared to the conventional double-layer photonic synaptic structure, our triple-layer device significantly reduces the recombination rate, resulting in improved performance in terms of the output photocurrent and memory characteristics. Furthermore, our photonic synaptic transistor possesses excellent synaptic properties, such as paired-pulse facilitation (PPF), short-term potentiation (STP), and long-term potentiation (LTP), and demonstrates a good response to a low operating voltage of − 0.1 mV. The low power consumption experiment shows a very low energy consumption of 0.01375 fJ per spike. These findings suggest a way to improve the performance of future neuromorphic devices and artificial vision systems.
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- 2023
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3. Editorial for the Special Issue on Graphene-Nanocomposite-Based Flexible Supercapacitors
- Author
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Prashant Shivaji Shewale and Kwang-Seok Yun
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n/a ,Mechanical engineering and machinery ,TJ1-1570 - Abstract
The evolution of hybrid materials has revolutionized the field of material science, particularly with the development of nanocomposites [...]
- Published
- 2024
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4. RGO decorated N-doped NiCo2O4 hollow microspheres onto activated carbon cloth for high-performance non-enzymatic electrochemical glucose detection
- Author
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Prashant Shivaji Shewale and Kwang-Seok Yun
- Subjects
NiCo2O4 ,RGO ,Composite ,N-doping ,Non-enzymatic ,Glucose detection ,Science (General) ,Q1-390 ,Social sciences (General) ,H1-99 - Abstract
This paper reports the first effective fabrication of a high-performance non-enzymatic glucose sensor based on activated carbon cloth (ACC) coated with reduced graphene oxide (RGO) decorated N-doped urchin-like nickel cobaltite (NiCo2O4) hollow microspheres. Hierarchically mesoporous N-doped NiCo2O4 hollow microspheres were synthesized using a facile solvothermal method, followed by thermal treatment in a nitrogen (N2) atmosphere. Subsequently, they were hydrothermally decorated with RGO nanoflakes. The resulting composite was dip-coated onto ACC, and its electrochemical and glucose sensing performances were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometric measurements in a three-electrode system. The composite electrode sensor demonstrates admirable sensitivity (6122 μM mM−1 cm−2) with an ultralow detection limit (5 nM, S/N = 3), and it performs well within a substantial linear range (0.5–1.450 mM). Additionally, it exhibits good long-term response stability and outstanding anti-interference performance. These outstanding results can be attributed to the synergistic effects of the highly electrically conductive ACC with multiple channels, the enhanced catalytic activity of highly porous N-doped NiCo2O4 hollow microspheres, and the large electroactive sites provided by its well-developed hierarchical nanostructure and RGO nanoflakes. The findings highlight the enormous potential of the ACC/N-doped NiCo2O4@RGO electrode for non-enzymatic glucose sensing.
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- 2023
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5. Three-Axis Pneumatic Haptic Display for the Mechanical and Thermal Stimulation of a Human Finger Pad
- Author
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Eun-Hyuk Lee, Sang-Hoon Kim, and Kwang-Seok Yun
- Subjects
haptic ,tactile ,shear ,thermal ,pneumatic ,Materials of engineering and construction. Mechanics of materials ,TA401-492 ,Production of electric energy or power. Powerplants. Central stations ,TK1001-1841 - Abstract
Haptic displays have been developed to provide operators with rich tactile information using simple structures. In this study, a three-axis tactile actuator capable of thermal display was developed to deliver tactile senses more realistically and intuitively. The proposed haptic display uses pneumatic pressure to provide shear and normal tactile pressure through an inflation of the balloons inherent in the device. The device provides a lateral displacement of ±1.5 mm for shear haptic feedback and a vertical inflation of the balloon of up to 3.7 mm for normal haptic feedback. It is designed to deliver thermal feedback to the operator through the attachment of a heater to the finger stage of the device, in addition to mechanical haptic feedback. A custom-designed control module is employed to generate appropriate haptic feedback by computing signals from sensors or control computers. This control module has a manual gain control function to compensate for the force exerted on the device by the user’s fingers. Experimental results showed that it could improve the positional accuracy and linearity of the device and minimize hysteresis phenomena. The temperature of the device could be controlled by a pulse-width modulation signal from room temperature to 90 °C. Psychophysical experiments show that cognitive accuracy is affected by gain, and temperature is not significantly affected.
- Published
- 2021
- Full Text
- View/download PDF
6. NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor
- Author
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Prashant Shivaji Shewale and Kwang-Seok Yun
- Subjects
wire ,flexible ,supercapacitor ,NiCo2O4 ,RGO ,Chemistry ,QD1-999 - Abstract
In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.
- Published
- 2021
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7. Fiber-Shaped Supercapacitors Fabricated Using Hierarchical Nanostructures of NiCo2O4 Nanoneedles and MnO2 Nanoflakes on Roughened Ni Wire
- Author
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Jing Zhang, Prashant S. Shewale, and Kwang-Seok Yun
- Subjects
Fiber-shaped supercapacitors ,hierarchical nanostructures ,NiCo2O4 nanoneedles ,MnO2 nanoflakes ,flexible supercapacitor ,Technology - Abstract
Electrostatic capacitors have high power density but low energy density. In contrast, batteries and fuel cells have high energy density but low power density. However, supercapacitors can simultaneously achieve both high power density and energy density. Herein, we propose a supercapacitor, in which etched nickel wire was used as a current collector due to its high conductivity. Two redox reactive materials, MnO2 nanoflakes and NiCo2O4 nanoneedles, were used in a hierarchical structure to cover the roughened surface of the Ni wire to maximize the effective surface area. Thus, a specific capacitance, energy density, and power density of 14.4 F/cm3, 2 mWh/cm3, and 0.1 W/cm3, respectively, was obtained via single-electrode experiments. A fiber-shaped supercapacitor was prepared by twisting two electrodes with solid electrolytes made of KOH and polyvinyl alcohol. Although the solid electrolyte had a low ionic conductivity, the energy density and power density were determined to be 0.97 mWh/cm3 and 49.8 mW/cm3, respectively.
- Published
- 2019
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8. Multifunctional Woven Structure Operating as Triboelectric Energy Harvester, Capacitive Tactile Sensor Array, and Piezoresistive Strain Sensor Array
- Author
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Kihong Kim, Giyoung Song, Cheolmin Park, and Kwang-Seok Yun
- Subjects
smart fabric ,triboelectric energy harvester ,capacitive sensors ,tactile sensors ,strain sensors ,Chemical technology ,TP1-1185 - Abstract
This paper presents a power-generating sensor array in a flexible and stretchable form. The proposed device is composed of resistive strain sensors, capacitive tactile sensors, and a triboelectric energy harvester in a single platform. The device is implemented in a woven textile structure by using proposed functional threads. A single functional thread is composed of a flexible hollow tube coated with silver nanowires on the outer surface and a conductive silver thread inside the tube. The total size of the device is 60 × 60 mm2 having a 5 × 5 array of sensor cell. The touch force in the vertical direction can be sensed by measuring the capacitance between the warp and weft functional threads. In addition, because silver nanowire layers provide piezoresistivity, the strain applied in the lateral direction can be detected by measuring the resistance of each thread. Last, with regard to the energy harvester, the maximum power and power density were measured as 201 μW and 0.48 W/m2, respectively, when the device was pushed in the vertical direction.
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- 2017
- Full Text
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9. ECG Monitoring Garment Using Conductive Carbon Paste for Reduced Motion Artifacts
- Author
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Jin-Woo Lee and Kwang-Seok Yun
- Subjects
electrocardiogram ,wearable ,graphite paste ,garment ,Organic chemistry ,QD241-441 - Abstract
The heart is a fundamental organ of the human circulatory system and the continuous measurement of electrocardiogram (ECG) signals is of great importance for pre-detection of heart diseases. Dry electrodes that do not require electrolyte gel have been developed for wearable ECG monitoring applications. However, this kind of electrode often introduces motion artifacts because of the high contact impedance between the electrode and skin. We propose a wearable ECG monitoring garment that employs electrodes made of conductive carbon-based paste. This paste is directly applied to the skin and after drying for 5 min, it forms a patch electrode that is detachable and flexible. The contact impedance between the patch electrode and the skin is very low because the paste covers the skin in a conformal manner. The experimental results show that the contact area of the carbon-based paste on the skin replica is almost 100%. At frequencies under 10 Hz, the contact impedance of the patch electrode is of 70.0 kΩ, much lower than the typical 118.7 kΩ impedance of a Ag/AgCl electrode. We also demonstrate that the ECG signals measured using the custom-designed garment and the patch electrodes are very stable even during actions such as walking and running.
- Published
- 2017
- Full Text
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10. Helical Piezoelectric Energy Harvester and Its Application to Energy Harvesting Garments
- Author
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Minsung Kim and Kwang-Seok Yun
- Subjects
piezoelectric energy harvester ,helical ,energy harvesting garment ,human body motions ,wearable ,Mechanical engineering and machinery ,TJ1-1570 - Abstract
In this paper, we propose a helical piezoelectric energy harvester, examine its application to clothes in the form of an energy harvesting garment, and analyze its design and characteristics. The helical harvester is composed of an elastic core and a polymer piezoelectric strap twining the core. The fabricated harvester is highly elastic and can be stretched up to 158% of its initial length. Following the experiments using three different designs, the maximum output power is measured as 1.42 mW at a 3 MΩ load resistance and 1 Hz motional frequency. The proposed helical harvesters are applied at four positions of stretchable tight-fitting sportswear, namely shoulder, arm joint, knee, and hip. The maximum output voltage is measured as more than 20 V from the harvester at the knee position during intended body motions. In addition, electric power is also generated from this energy harvesting garment during daily human motions, which is about 3.9 V at the elbow, 3.1 V at the knee, and 4.4 V at the knee during push-up, walking, and squatting motions, respectively.
- Published
- 2017
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11. Flexible Textile Structures Composed of Various Functional Threads and Managing Circuitry for Self-Powered Wearable Sensor System.
- Author
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Eunhyuk Lee, Kihong Kim, JaeHo Han, and Kwang-Seok Yun
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- 2024
- Full Text
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12. Triboelectric energy harvester in hollow tube structure and its sensor property.
- Author
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Ki-Hong Kim and Kwang-Seok Yun
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- 2017
- Full Text
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13. Tactile display with tangential and normal skin displacement for robot-assisted surgery.
- Author
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Soo-Chul Lim, Hyungkew Lee, Eunhyup Doh, Kwang-Seok Yun, and Joonah Park
- Published
- 2014
- Full Text
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14. Room-temperature hydrogen gas sensor composed of palladium thin film deposited on NiCo2O4 nanoneedle forest
- Author
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Sang-Hoon Kim and Kwang-Seok Yun
- Subjects
Materials Chemistry ,Metals and Alloys ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Instrumentation ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2023
15. Ternary Nanocomposites of Pedot: Pss, Rgo, and Urchin-Like Hollow Microspheres of Nico2o4 for Flexible and Weavable Supercapacitors
- Author
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Prashant Shivaji Shewale and Kwang-Seok Yun
- Subjects
Mechanics of Materials ,Mechanical Engineering ,General Materials Science ,Condensed Matter Physics - Published
- 2022
16. Surface modified Ni wire supported flexible asymmetric supercapacitor of Mn3O4// PEDOT-PSS-MWCNT and its solar charging for self-powered Cu-doped ZnO nanorods-based UV photodetector
- Author
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Prashant Shivaji Shewale and Kwang-Seok Yun
- Subjects
Mechanics of Materials ,Mechanical Engineering ,Materials Chemistry ,Metals and Alloys - Published
- 2022
17. Multifunctional Woven Structure Operating as Triboelectric Energy Harvester, Capacitive Tactile Sensor Array, and Piezoresistive Strain Sensor Array.
- Author
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Ki-Hong Kim, Giyoung Song, Cheolmin Park, and Kwang-Seok Yun
- Published
- 2017
- Full Text
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18. Stretchable Power-Generating Sensor Array in Textile Structure Using Piezoelectric Functional Threads with Hemispherical Dome Structures
- Author
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Kihong Kim and Kwang-Seok Yun
- Subjects
0209 industrial biotechnology ,Materials science ,Renewable Energy, Sustainability and the Environment ,business.industry ,Mechanical Engineering ,Capacitive sensing ,02 engineering and technology ,Thread (computing) ,021001 nanoscience & nanotechnology ,Piezoelectricity ,Piezoresistive effect ,Industrial and Manufacturing Engineering ,020901 industrial engineering & automation ,Sensor array ,Management of Technology and Innovation ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Energy harvesting ,Triboelectric effect ,Tactile sensor - Abstract
This paper presents a power-generating sensor array in a flexible and stretchable form. The proposed device is composed of a woven structure that provides various features, including a capacitive tactile sensor, piezoresistive strain sensor, triboelectric energy harvester, and piezoelectric energy harvester. The device is implemented in a textile structure using functional threads implemented with lead zirconate, carbon nanotube, polydimethylsiloxane, and silver nanowire (Ag NW). A stretching force can be detected by measuring the resistance change in the Ag NW composite layer on each thread. Further, the magnitude and location of the vertical force can be detected by measuring the capacitance variation on each capacitive cell that is formed by the gap between two Ag NW layers at the crossing points of each weft and warp thread. For the energy harvesters, the maximum power was measured as 108 μW at 3 MΩ from the triboelectric energy harvesting when the device was pushed in the vertical direction. When a stretching force was applied, a maximum of 60.3 μW at 1 MΩ was measured from the piezoelectric energy harvester.
- Published
- 2019
19. NiCo2O4/RGO Hybrid Nanostructures on Surface-Modified Ni Core for Flexible Wire-Shaped Supercapacitor
- Author
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Kwang-Seok Yun and P.S. Shewale
- Subjects
Supercapacitor ,Materials science ,Equivalent series resistance ,Graphene ,General Chemical Engineering ,wire ,NiCo2O4 ,Electrolyte ,Electrochemistry ,Capacitance ,law.invention ,lcsh:Chemistry ,Chemical engineering ,lcsh:QD1-999 ,law ,RGO ,Electrode ,General Materials Science ,supercapacitor ,flexible ,Power density - Abstract
In this work, we report surface-modified nickel (Ni) wire/NiCo2O4/reduced graphene oxide (Ni/NCO/RGO) electrodes fabricated by a combination of facile solvothermal and hydrothermal deposition methods for wire-shaped supercapacitor application. The effect of Ni wire etching on the microstructural, surface morphological and electrochemical properties of Ni/NCO/RGO electrodes was investigated in detail. On account of the improved hybrid nanostructure and the synergistic effect between spinel-NiCo2O4 hollow microspheres and RGO nanoflakes, the electrode obtained from Ni wire etched for 10 min, i.e., Ni10/NCO/RGO exhibits the lowest initial equivalent resistance (1.68 Ω), and displays a good rate capability with a volumetric capacitance (2.64 F/cm3) and areal capacitance (25.3 mF/cm2). Additionally, the volumetric specific capacitance calculated by considering only active material volume was found to be as high as 253 F/cm3. It is revealed that the diffusion-controlled process related to faradaic volume processes (battery type) contributed significantly to the surface-controlled process of the Ni10/NCO/RGO electrode compared to other electrodes that led to the optimum electrochemical performance. Furthermore, the wire-shaped supercapacitor (WSC) was fabricated by assembling two optimum electrodes in-twisted structure with gel electrolyte and the device exhibited 10 μWh/cm3 (54 mWh/kg) energy density and 4.95 mW/cm3 (27 W/kg) power density at 200 μA. Finally, the repeatability, flexibility, and scalability of WSCs were successfully demonstrated at various device lengths and bending angles.
- Published
- 2021
20. Fully elastic multilayered triboelectric energy harvester made of polymer thin films and elastic tubes
- Author
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Kihong Kim and Kwang-Seok Yun
- Subjects
Materials science ,Mechanics of Materials ,Signal Processing ,General Materials Science ,Electrical and Electronic Engineering ,Composite material ,Condensed Matter Physics ,Polymer thin films ,Atomic and Molecular Physics, and Optics ,Energy harvester ,Triboelectric effect ,Civil and Structural Engineering - Published
- 2021
21. Fabrication of Pseudo-Palladium Nanostructures and Its Application to Hydrogen Gas Sensor
- Author
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Sanghoon Kim and Kwang-Seok Yun
- Subjects
Materials science ,Fabrication ,Nanostructure ,Hydrogen ,business.industry ,chemistry.chemical_element ,Conductance ,Response time ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Hydrothermal circulation ,0104 chemical sciences ,chemistry ,Optoelectronics ,0210 nano-technology ,business ,Pseudo palladium ,Palladium - Abstract
Nano-structured palladium (Pd) is advantageous in the sensitive detection of hydrogen because of its large surface area. However, the formation of Pd nanostructure is not easy but requires expensive and complicated processes. In this work, we proposed hydrothermal growing of nano-needles and its application to hydrogen gas sensor. In this way, the physical parameters of the nanostructures such as length and diameter can be easily controlled during the hydrothermal process. In addition, fast response time and high sensitivity can be obtained because the hydrogen gas can be easily absorbed into the thin Pd layer resulting in the fast and steep change of the conductance.
- Published
- 2019
22. Capacitive Force Sensor with Wide Dynamic Range Using Wrinkled Micro Structures as Dielectric Layer
- Author
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Chan-Hoon Na and Kwang-Seok Yun
- Subjects
Materials science ,Dynamic range ,Capacitive sensing ,Biomedical Engineering ,Bioengineering ,General Chemistry ,Substrate (electronics) ,Dielectric ,Condensed Matter Physics ,Elastomer ,Capacitance ,Electrode ,Wide dynamic range ,General Materials Science ,Composite material - Abstract
We propose a wide dynamic range capacitive force sensor with two wrinkle-structured elastomer layers as a dielectric layer. The sensor consists of electrodes on each substrate and two dielectric layers between them. The electrode is made of platinum and fabricated by using a lift-off process. The polyimide film is used as a substrate. Two wrinkle-structured dielectric layers, which are placed in perpendicular direction, are made by poly(dimethylsiloxane) (PDMS) replica molding process. With the pressure applied on the device, dielectric layers deform while decreasing distance between the electrodes and thus increasing the capacitance of the sensor. The orthogonally positioned wrinkled structures make possible to increase the dynamic range of the capacitive cell. The proposed capacitive sensor operates in the pressure range of 1 MPa with the maximum sensitivity of 0.06%/kPa.
- Published
- 2019
23. NICO2O4@MNO2 Double Nanostructures Grown on Etched Nickel Wire for Fiber-Shaped Super-Capacitors Applications
- Author
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Kwang-Seok Yun and Jing Zhang
- Subjects
Nanostructure ,Materials science ,chemistry.chemical_element ,High capacity ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Nickel ,Capacitor ,chemistry ,Chemical engineering ,law ,Electrode ,Hydrothermal synthesis ,Fiber ,0210 nano-technology - Abstract
We report a “dual nanostructures” where MnO 2 nano-hairs cover NiCo 2 O 4 nano-needles forming NiCo 2 O 4 @MnO 2 double nanostructures. The NiCo 2 O 4 @MnO 2 double nanostructures were synthesized by simple two-steps hydrothermal synthesis on the etched surface of nickel (Ni) wire. These structures were applied to form high capacity of fiber-shaped super-capacitor which was fully fabricated and demonstrated in this work.
- Published
- 2019
24. An Exploratory Study on the Feasibility of a Foot Gear Type Energy Harvester Using a Textile Coil Inductor
- Author
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Hyun Seung Cho, Yong Jun Kim, Joo Hyeon Lee, Kwang-Seok Yun, Seon Hyung Park, and Jin Hee Yang
- Subjects
010302 applied physics ,Engineering ,business.industry ,Electrical engineering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Inductor ,01 natural sciences ,Coil spring ,Power (physics) ,Generator (circuit theory) ,Electromagnetic coil ,0103 physical sciences ,Electrical and Electronic Engineering ,Oscilloscope ,0210 nano-technology ,business ,Energy harvesting ,Voltage - Abstract
This research developed a textile coil inductor, in which conductive yarn was wound spirally onto textile, and produced an energy harvesting module utilizing a cylindrical compression coil spring structure to allow a permanent magnet to spin in the center hole of the coil inductor. The study confirmed through a pilot test that the voltage increased as the number of laminated layers of the coil inductor increased. Five subjects were tested in the energy harvesting measuring experiment after producing a sports shoe insole-mounted energy harvesting module. While the subjects executed sports motions such as walking and running at five given frequencies, the peak-to-peak voltage was measured by an oscilloscope and the accumulated energy voltage of the calculated rms voltage (Vrms) and the peak power (㎼) were derived. The output voltage increased as the frequency increased and the average Vp-p (V) of the five subjects was 0.53 V, the average peak power (㎼) was 0.289 ㎼, and the Vrms (V) was 0.065 V. This research is significant in that it suggests the possibility of an energy harvesting module based upon the textile coil inductor emerging from the former shoes’ energy generator packaging method for heavy shoe types by developing a lightweight, flexible, and human-friendly footgear module structure.
- Published
- 2016
25. Enzymeless glucose sensor integrated with chronically implantable nerve cuff electrode for in-situ inflammation monitoring
- Author
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Sung Jin Park, Soo Hyun Lee, Yi Jae Lee, Ji Yoon Kang, and Kwang-Seok Yun
- Subjects
In situ ,Working electrode ,Materials science ,010401 analytical chemistry ,Metals and Alloys ,Cuff electrode ,Inflammation ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Signal ,Amperometry ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,Materials Chemistry ,medicine ,Sciatic nerve ,Electrical and Electronic Engineering ,medicine.symptom ,0210 nano-technology ,Instrumentation ,Biomedical engineering - Abstract
Using glucose concentration as an inflammation responsive element, we newly established an enzymeless glucose sensor integrated with a chronically implantable peripheral nerve cuff electrode for continuous and in-situ monitoring of local inflammation. The glucose sensor integrated with a nerve cuff electrode was fabricated on a polyimide substrate side-by-side, then the glucose sensor and nerve cuff electrode were reversely folded, and were located inside and outside, respectively. The experimental results reveal that the electroplated black Pt working electrode of the glucose sensor shows an enhancive surface roughness factor of 16.41 and had a good distribution on the flexible polyimide surface, which exhibits distinctly enhanced electro-catalytic activity compared to that obtained with plain Pt. Amperometry and electrochemical impedance spectroscopy indicated that the fabricated sensor had a sensitivity of 7.17 μA/mM cm 2 , an outstanding detection limit of 10 μM, significant selectivity, and excellent recovery performance for enzymeless glucose detection. In order to evaluate the feasibility for inflammation monitoring in the immediate vicinity of the implantable peripheral nerve cuff electrode, the association of an evoked nerve signal recording and glucose concentration was investigated through ex-vivo test using the sciatic nerve of a SD rat.
- Published
- 2016
26. Development of Novel Implantable Intraocular Pressure Sensors to Enhance the Performance in in vivo Tests
- Author
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Kwang-Seok Yun, Mi Jeung Kim, Kyeong-Sik Shin, Soo Hyun Lee, Ji Yoon Kang, Ki Ho Park, and Cheol-In Jang
- Subjects
Intraocular pressure ,Materials science ,Mechanical Engineering ,Capacitive sensing ,Capacitance ,law.invention ,Inductance ,Responsivity ,Capacitor ,In vivo ,law ,Electronic engineering ,Sensitivity (control systems) ,Electrical and Electronic Engineering ,Biomedical engineering - Abstract
In this paper, we proposed a dual-mode intraocular pressure (IOP) sensor that has two separated diaphragms to conduct the changes of inductance and capacitance, and we compared the sensor’s performance with that of the conventional single variable capacitive sensor (single-mode sensor). Both mode sensors were used to monitor the pressure in in vitro tests with multiple media and in in vivo tests with rabbits. First, we demonstrated that the sensitivities of two types of sensors tended to be different for in vivo and in vitro tests. This was the first known attempt to show changes in the sensitivity and responsivity of IOP sensors in in vivo tests. The sensitivity and phase dip of the dual-mode sensor exceeded that of the single-mode sensor, irrespective of medium due to isolation of capacitive sensor from medium. In this paper, we have provided the equations that were used to evaluate the improvement in sensitivity, and we have shown the coincidence with in vitro and in vivo tests. Based on the results we achieved, we believe that the dual-mode sensor is more feasible for use as an IOP sensor in in vivo tests, because its responsivity and sensitivity are superior to those of the conventional sensors. [2014-0379]
- Published
- 2015
27. Synthesis and characterization of Cu-doped ZnO/RGO nanocomposites for room-temperature H2S gas sensor
- Author
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Kwang-Seok Yun and P.S. Shewale
- Subjects
Nanostructure ,Materials science ,Nanocomposite ,Dopant ,Graphene ,Mechanical Engineering ,Metals and Alloys ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Zinc ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Crystallinity ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Mechanics of Materials ,law ,Materials Chemistry ,0210 nano-technology ,Deposition (law) - Abstract
The development of low or room temperature gas sensors having a response towards a particular target gas becomes a fascinating research topic for low power consumption applications. In this paper, a sensitive room-temperature hydrogen sulfide (H2S) gas sensors based on hydrothermally synthesized undoped zinc oxide (ZnO) and Cu-doped ZnO (CZO) nanostructures decorated with reduced graphene oxide (RGO) are successfully demonstrated. A simple air-spray deposition is employed as an effective method for uniform GO decoration on CZO nanostructured film which is further chemically reduced to form RGO. The influence of Cu-doping on crystallinity, surface-morphological, and chemical compositional properties of the material have been systematically investigated. The gas sensing properties of the synthesized nanocomposite sensors have been studied towards H2S at room temperatures (∼24 °C). Compared with undoped ZnO/RGO, 3CZO/RGO nanocomposite sensor exhibited a better response towards H2S. The sensor response increases almost linearly with the increase in H2S gas concentration and exhibits the evident response of 0.87%–100 ppm H2S at 24 °C with the response and recovery time of 14 and 32 s, and a theoretical limit of detection of about 136 ppb. The enhancement was accredited to the collegial effect of both Cu dopant and RGO. The sensor also shows good selective behavior towards H2S against H2. The H2S sensing mechanism associated with the p-type behavior of the 3CZO/RGO sensor is also discussed at length.
- Published
- 2020
28. Functional nerve cuff electrode with controllable anti-inflammatory drug loading and release by biodegradable nanofibers and hydrogel deposition
- Author
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Ji Yoon Kang, Soo Hyun Lee, Dong Nyoung Heo, Il Keun Kwon, Sung Jin Park, Yi Jae Lee, and Kwang-Seok Yun
- Subjects
Conductive polymer ,Metals and Alloys ,Polyethylene glycol ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,PLGA ,chemistry ,PEDOT:PSS ,Nanofiber ,Electrode ,PEG ratio ,Materials Chemistry ,Sciatic nerve ,Electrical and Electronic Engineering ,Instrumentation ,Biomedical engineering - Abstract
This paper demonstrates a polyimide nerve cuff electrode with a controllable drug loading/release function for stable recording of peripheral nerve signals and stimulation and minimizing inflammation. For control of anti-inflammatory drug loading/release, dexamethasone (DEX)-loaded poly L -lactic acid (PLLA) and/or poly lactic-co-glycol acid (PLGA) nanofibers were deposited on a functional nerve cuff electrode by the electro-spinning method, which can control the weight of DEX loading on the functional nerve cuff electrode. Then, UV patternable polyethylene glycol (PEG) was coated on the functional nerve cuff with DEX-loaded nanofibers for the acceleration of the release rate of the drug. Through high performance liquid chromatography (HPLC), DEX release rates were increased from 16 to 28% (PLLA-loaded nanofibers) and from 68 to 87% (PLGA-loaded nanofibers) due to the increased diffusion rate of DEX after 28 days, respectively. In addition, the functional nerve cuff electrode was electro-polymerized with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as a conductive polymer in order to recover the decreased electrical properties caused by PEG patterning. The impedance measured at 1 kHz was 342 Ω mm2, which was extremely lower than the value of 1046 Ω mm2 of PEG-patterned cuff electrodes. Through the acute ex-vivo test of SD rat's sciatic nerve, the functional nerve cuff electrode with PEDOT:PSS exhibited stable and effective recording of the nerve's signals despite PEG patterning.
- Published
- 2015
29. A flexible multimodal tactile display array for virtual shape and texture
- Author
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Eui-Sung Yoon, Kyungwhan Na, Euntai Kim, Choonghyun Son, Ji-Seok Han, Il-Joo Cho, Hyunjoo Lee, Kwang-Seok Yun, and Kyungmin Ko
- Subjects
010302 applied physics ,Engineering ,InformationSystems_INFORMATIONINTERFACESANDPRESENTATION(e.g.,HCI) ,business.industry ,Vibration amplitude ,02 engineering and technology ,Virtual reality ,Texture (music) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Tactile display ,Displacement (vector) ,Electronic, Optical and Magnetic Materials ,Hardware and Architecture ,0103 physical sciences ,Wide dynamic range ,Computer vision ,Artificial intelligence ,Electrical and Electronic Engineering ,0210 nano-technology ,Actuator ,business ,Tactile sensor - Abstract
Multimodal tactile display systems that are capable of delivering versatile tactile information effectively are of great interest for virtual reality and tele-operation applications. In this paper, we present a new flexible multimodal tactile display system that delivers shape and texture information simultaneously using a single actuator. The proposed tactile display is actuated by a combination of electromagnetic and pneumatic forces and thus exhibits high tactile force to deliver shape information and large vibration amplitude to deliver texture information. In addition, the proposed tactile display device was implemented on a flexible PDMS structure to allow for tight attachment on any curved body to transfer reliable tactile information. By applying a current pulse of 300 mA for 5 ms, we readily controlled the state of the tactile actuator and measured the actuation displacement of 900 μm and the generated force of 20.1 gf. The average vibration amplitude of 30 μm was measured over a wide dynamic range (25---650 Hz) with an applied current of 74 mA. Lastly, by delivering various tactile information to users, we verified the functionalities of the implemented 4 ? 1 multimodal tactile display array. User study results showed that the fabricated multimodal tactile display system successfully delivered both shape information with an accuracy of 73 % and texture information with an accuracy of 90 %. This work demonstrates the potential of our multimodal tactile display system for uses in various applications such as tele-operation, tactile communication, and visual presentation for visually impaired.
- Published
- 2015
30. Position controlled pneumatic tactile display for tangential stimulation of a finger pad
- Author
-
Soo-Chul Lim, Seokpyo Yun, Jihyung Yoo, Kwang-Seok Yun, Joonah Park, and Hyung-Kew Lee
- Subjects
Engineering ,Pneumatic actuator ,business.industry ,Feedback control ,Acoustics ,Capacitive sensing ,Metals and Alloys ,Condensed Matter Physics ,Flexible electronics ,Tactile display ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Position (vector) ,Control theory ,Electrical and Electronic Engineering ,business ,Instrumentation ,Position control ,Position sensor - Abstract
This paper presents the design and implementation of a pneumatic tactile display with a Flexible Printed Circuit Board (FPCB) based capacitive position sensor integrated for precise position control. The proposed tactile display was designed to stimulate human finger in tangential direction. The size of the fabricated display was 18 mm × 18 mm × 20 mm. The position control range was 2.5 mm for each x and y axis. The resolution of position control was estimated from three repeated experiments as 0.12 mm with feedback control. The hysteresis behavior of the proposed display observed before feedback control has been eliminated.
- Published
- 2015
31. Implantable Nerve Cuff Electrode with Conductive Polymer for Improving Recording Signal Quality at Peripheral Nerve
- Author
-
Ji Yoon Kang, Kwang-Seok Yun, Soo Hyun Lee, Sung Jin Park, and Yi Jae Lee
- Subjects
Conductive polymer ,Materials science ,Signal quality ,PEDOT:PSS ,Electrode ,Cuff electrode ,Sciatic nerve ,Cyclic voltammetry ,Signal ,Biomedical engineering - Abstract
This study demonstrates a polyimide nerve cuff electrode with a conductive polymer for improving recording signal quality at periph-eral nerve. The nerve cuff electrodes with platinum (Pt), iridium oxide (IrOx), and poly(3,4-ethylenedioxythiophene): p-toluene sul-fonate (PEDOT:pTS) were fabricated and investigated their electrical characteristics for improving recorded nerve signal quality. Thefabricated nerve cuff electrodes with Pt, IrOx, and PEDOT:pTS were characterized their impedance and CDC by using electrochemicalimpedance spectroscopy (EIS) and cyclic voltammetry. The impedance of PEDOT:pTS measured at 1 kHz was 257Ω, which wasextremely lower than the value of the nerve cuff electrodes with IrOx (15897 Ω) and Pt (952Ω), respectively. Furthermore, the chargedelivery capacity (CDC) of the nerve cuff electrode with PEDOT:pTS was dramatically increased to 62 times than the nerve cuff elec-trode with IrOx. In ex-vivo test using extracted sciatic nerve of spaque-dawley rat (SD rat), the PEDOT:pTS group exhibited higher sig-nal-to-interference ratio than IrOx group. These results indicated that the nerve cuff electrode with PEDOT:pTS is promising foreffective implantable nerve signal recording.Keywords: Nerve cuff electrode, Neural signal recording, Iridium oxide, PEDOT:pTS, ex-vivo test
- Published
- 2015
32. Three-axis pneumatic tactile display with integrated capacitive sensors for feedback control
- Author
-
Kwang-Seok Yun, Seokpyo Yun, Jihyung Yoo, Soo-Chul Lim, Joonah Park, and Hyung-Kew Lee
- Subjects
Engineering ,business.industry ,Acoustics ,Capacitive sensing ,Capacitive displacement sensor ,Condensed Matter Physics ,GeneralLiterature_MISCELLANEOUS ,Flexible electronics ,Displacement (vector) ,Electronic, Optical and Magnetic Materials ,Core (optical fiber) ,03 medical and health sciences ,0302 clinical medicine ,Hardware and Architecture ,030220 oncology & carcinogenesis ,Control system ,Electronic engineering ,030211 gastroenterology & hepatology ,Electrical and Electronic Engineering ,business ,Tactile sensor ,ComputingMethodologies_COMPUTERGRAPHICS ,Haptic technology - Abstract
In this paper, we propose a three-axis pneumatic tactile display that is precisely controlled by using integrated capacitive displacement sensors. The proposed tactile display consists of a core body with a 3 × 3 balloon array on its top surface, four lateral balloons made of latex rubber, and inner and outer frames that include capacitive displacement sensors based on a flexible printed circuit board. The 3 × 3 balloon array on the core body is designed to apply normal haptic stimulation to a human fingertip. In addition, the lateral motions of the core body and each frame produce haptic stimulation in a tangential direction. Precise control of lateral motion was achieved by feedback control using the capacitive displacement sensors. The size of the fabricated tactile display was 26 × 26 × 18 mm3. We experimentally performed manipulation of the proposed device with a custom control system, thereby demonstrating accurate control of displacement.
- Published
- 2014
33. Development of Inductive and Capacitive Type Intraocular Pressure (IOP) Sensor to Improve Sensitivity and Minimize Size
- Author
-
Yong Woo Kim, Kwang-Seok Yun, Ji Yoon Kang, Kyeong-Sik Shin, Soo Hyun Lee, and Cheol In Jang
- Subjects
Intraocular pressure ,Materials science ,genetic structures ,business.industry ,Capacitive sensing ,Glaucoma ,medicine.disease ,eye diseases ,Micro coil ,Optics ,medicine ,sense organs ,Implant ,business ,Biomedical engineering - Abstract
We had presented an inductive type intraocular pressure sensor (L-sensor) in previous work. The distance between a micro coil anda ferrite on the membrane was modulated by pressure, and as a result the inductance and resonant frequency were changed. However,L-sensor has some problems to implant in eyes. First problem is low sensitivity. When L-sensor was implanted in rabbit’s eyes, resonantfrequency of L-sensor was very hard to detect. Second problem is biocompatibility. Size of L-sensor is 6×7×1.2 mm. When L-sensorwas implanted in the eyes, it caused the inflammation. Therefore, this study suggests an inductive and capacitive type IOP sensor (LC-sensor). The sensitivity of the LC-sensor 27.3 kHz/mmHg under 60 mmHg. It is much larger than 14 kHz/mmHg of the L-sensor. Andthe size of LC-sensor is 47% smaller than L-sensor. After 2 weeks from the implantation of LC-sensor into rabbit eyes, we measuredthe changes of resonant frequency of LC-sensor according to increased IOP by Balanced Salt Solution (BSS) injection. As a result, thesensitivity of LC-sensor in in vivo test is 25 kHz/mmHg. That is similar to the sensitivity of in vitro test.Keywords: Glaucoma, Intraocular pressure (IOP), IOP sensor, in vivo, Wireless, Implantable
- Published
- 2014
34. Triboelectric energy harvester in hollow tube structure and its sensor property
- Author
-
Kihong Kim and Kwang-Seok Yun
- Subjects
Materials science ,business.industry ,Capacitive sensing ,Nanotechnology ,02 engineering and technology ,Strain sensor ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoresistive effect ,Energy harvester ,0104 chemical sciences ,Power (physics) ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) ,Triboelectric effect ,Voltage - Abstract
We propose flexible triboelectric energy harvester having a strain sensor property having hollow tube structure. The device was implemented by using flexible silicone tube where the silver nanowire layer is deposited on outer surface. When the tube is pressed or strained in axial direction, output power is generated by triboelectric effect. The output voltage and power of this device was measured as 23.4 V and 201 µW at 3 Hz. In addition, the device shows a piezoresistive property when longitudinal force is applied, which can be utilized as strain sensor that can be detected by measuring the resistance of the wires.
- Published
- 2017
35. Piezoelectric energy harvester using mechanical frequency up conversion for operation at low-level accelerations and low-frequency vibration
- Author
-
Dongjae Han and Kwang-Seok Yun
- Subjects
Engineering ,Cantilever ,business.industry ,Acoustics ,Bandwidth (signal processing) ,Structural engineering ,Condensed Matter Physics ,Piezoelectricity ,Electronic, Optical and Magnetic Materials ,Vibration ,Buckling ,Hardware and Architecture ,Electrical and Electronic Engineering ,Proof mass ,business ,Energy harvesting ,Excitation - Abstract
In this paper, we propose a modified frequency up-conversion mechanism to lower the operational acceleration level for energy harvesting devices using a snap-through buckling phenomenon. The proposed device consists of a buckled bridge beam clamped on flexible sidewalls with a proof mass and cantilever beams attached to the bridge. When subject to a vibration, the buckled bridge beam snaps through between two stable states, inducing impulsive acceleration on the attached piezoelectric cantilevers. During the snap-through transition, the flexible sidewalls deflect outward, thus lowering the threshold acceleration value for the state transition. Various sidewall materials with different flexibilities were tested to determine the maximum output power, bandwidth, and output characteristics for various input acceleration values. The minimum acceleration value for snap-through transition was 0.5g (g = 9.8 m/s2) when using latex sidewalls. A maximum output power of 0.4 mW Hz/cm2--that is 10 μW for test sample at an excitation frequency of 15 Hz--was generated by using the proposed device with latex sidewalls.
- Published
- 2014
36. Tactile display with tangential and normal skin displacement for robot-assisted surgery
- Author
-
Eunhyup Doh, Kwang-Seok Yun, Soo-Chul Lim, Joonah Park, and Hyung-Kew Lee
- Subjects
Engineering ,Normal force ,Pneumatic actuator ,business.industry ,Shear force ,Tactile display ,Computer Science Applications ,body regions ,Human-Computer Interaction ,Hardware and Architecture ,Control and Systems Engineering ,Teleoperation ,Robot ,Displacement (orthopedic surgery) ,Computer vision ,Artificial intelligence ,business ,Software ,Haptic technology - Abstract
This paper proposes a tactile display providing both shear and normal feedback to the fingertip for generating three-axis tactile feedback during teleoperation of a surgical robot. The display is composed of five balloons actuated by controlling the pneumatic pressure. The implemented display is 18 mm × 18 mm × 15 mm. This size is suitable for mounting the display onto the master controls of a surgical robot. The maximum normal and shear displacements are 2 and 1.3 mm, respectively. The proposed tactile display may provide perceivable stimuli to a human finger pad in all five directions: normal, distal, proximal, radial, and ulnar. This paper also reports on the results of psychophysical measurement of the minimum perceivable movement of the developed tactile display for each of the five directions.
- Published
- 2014
37. Fiber-Shaped Supercapacitors Fabricated Using Hierarchical Nanostructures of NiCo2O4 Nanoneedles and MnO2 Nanoflakes on Roughened Ni Wire
- Author
-
P.S. Shewale, Kwang-Seok Yun, and Jing Zhang
- Subjects
Control and Optimization ,Materials science ,Energy Engineering and Power Technology ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,flexible supercapacitor ,lcsh:Technology ,01 natural sciences ,Capacitance ,law.invention ,law ,Fast ion conductor ,Electrical and Electronic Engineering ,Composite material ,Engineering (miscellaneous) ,Power density ,Supercapacitor ,lcsh:T ,Renewable Energy, Sustainability and the Environment ,hierarchical nanostructures ,Current collector ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Fiber-shaped supercapacitors ,Capacitor ,NiCo2O4 nanoneedles ,MnO2 nanoflakes ,0210 nano-technology ,Energy (miscellaneous) ,Reactive material - Abstract
Electrostatic capacitors have high power density but low energy density. In contrast, batteries and fuel cells have high energy density but low power density. However, supercapacitors can simultaneously achieve both high power density and energy density. Herein, we propose a supercapacitor, in which etched nickel wire was used as a current collector due to its high conductivity. Two redox reactive materials, MnO2 nanoflakes and NiCo2O4 nanoneedles, were used in a hierarchical structure to cover the roughened surface of the Ni wire to maximize the effective surface area. Thus, a specific capacitance, energy density, and power density of 14.4 F/cm3, 2 mWh/cm3, and 0.1 W/cm3, respectively, was obtained via single-electrode experiments. A fiber-shaped supercapacitor was prepared by twisting two electrodes with solid electrolytes made of KOH and polyvinyl alcohol. Although the solid electrolyte had a low ionic conductivity, the energy density and power density were determined to be 0.97 mWh/cm3 and 49.8 mW/cm3, respectively.
- Published
- 2019
38. Electrostatic Energy Harvester Using Magnetically Actuated Liquid Dielectric Layers
- Author
-
Kwang-Seok Yun, Seonuk Yu, Byeong-Geun Kang, and Dong-Il Kim
- Subjects
Ferrofluid ,Materials science ,business.industry ,Mechanical Engineering ,Electric potential energy ,Liquid dielectric ,Electrical engineering ,Rotational speed ,Dielectric ,Electrostatics ,Capacitance ,Magnetic field ,Optoelectronics ,Electrical and Electronic Engineering ,business - Abstract
We propose a fully liquid-based energy harvester that uses ferrofluid droplets as a movable dielectric material. The proposed device consists of top and bottom plates with conducting electrodes coated with a thin solid dielectric layer, a conducting liquid, and oil-based ferrofluid droplets as movable dielectric layers. The rotational motion of the ferrofluid droplets is actuated by a magnetic field that causes a capacitance variation that is used to generate electric power. An average output power of $19.3~\mu \text{W}$ is generated when eight ferrofluid droplets are used at a rotational speed of 180 r/min. [2014-0387]
- Published
- 2015
39. All-polymer hair structure with embedded three-dimensional piezoresistive force sensors
- Author
-
Dong-Il Kim, Kwang-Seok Yun, and Ji-Eun Han
- Subjects
chemistry.chemical_classification ,Materials science ,Fabrication ,Composite number ,Metals and Alloys ,chemistry.chemical_element ,Nanotechnology ,Polymer ,Substrate (electronics) ,Carbon nanotube ,Condensed Matter Physics ,Piezoresistive effect ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry ,Gauge factor ,law ,Electrical and Electronic Engineering ,Composite material ,Instrumentation ,Carbon - Abstract
This paper presents the design, fabrication, and experimental demonstration of an artificial hair sensor made of polymer materials. Long polymer hair structures embedded with flexible three-dimensional piezoresistive sensors were formed on a flexible substrate in two-dimensional arrays to detect an applied external force. The flexible piezoresistor was implemented using a carbon nanotube-polydimethylsiloxane (CNT-PDMS) composite prepared by the mixing of multi-wall carbon nanotubes with PDMS. A CNT-PDMS composite with high conductivity and a high gauge factor was obtained by increasing the CNT concentration in PDMS. In this study, we used a 13% CNT-PDMS composite for fabricating the sensing element that was embedded in the proposed hair sensor. The hair sensor is 4 mm in height and 700 μm in diameter. The implemented device shows a linear and sensitive response in the on-axis mode with a sensitivity of 2900 ppm/μm.
- Published
- 2012
40. Piezoelectric shell structures as wearable energy harvesters for effective power generation at low-frequency movement
- Author
-
Boram Yang and Kwang-Seok Yun
- Subjects
Engineering ,business.industry ,Electric potential energy ,Metals and Alloys ,Shell (structure) ,Mechanical engineering ,Folding (DSP implementation) ,Condensed Matter Physics ,Piezoelectricity ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Power (physics) ,Electrical and Electronic Engineering ,business ,Instrumentation ,Energy harvesting ,Energy (signal processing) ,Mechanical energy - Abstract
This paper discusses a flexible energy harvester that consists of a polyvinylidene fluoride film attached to a curved substrate in a shell shape for harvesting energy from human motion. The proposed harvester effectively converts mechanical energy into electrical energy during the fast state transition of the shell structure. The results of an experiment demonstrated that shell structures with various curvatures produce high output potential and consequently offer high output power in comparison to a simple flat structure. The single shell structure generates an output power of 0.87 mW at a folding angle of 80° and a folding and unfolding frequency of 3.3 Hz. In addition, fabric with embedded piezoelectric shell structures was designed as an energy harvester in a wearable platform. The fabric, worn on the elbow joints and fingers, generates a high output power of 0.21 mW in spite of slow and irregular motion.
- Published
- 2012
41. Nanostructure Modified Microelectrode for Electrochemical Detection of Dopamine with Ascorbic Acid and Uric Acid
- Author
-
Kwang-Seok Yun, Su-Hyun Pyo, Jeong-Woo Choi, Byung-Keun Oh, Jin-Ha Choi, Ji-Young Lee, and Kyeong-Jun Kim
- Subjects
Nanostructure ,Materials science ,Surface Properties ,Dopamine ,Biomedical Engineering ,Bioengineering ,Ascorbic Acid ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,medicine ,General Materials Science ,010401 analytical chemistry ,General Chemistry ,Condensed Matter Physics ,Ascorbic acid ,0104 chemical sciences ,Nanostructures ,Uric Acid ,Microelectrode ,chemistry ,Electrode ,Microscopy, Electron, Scanning ,Uric acid ,Selectivity ,Biosensor ,Microelectrodes ,medicine.drug ,Biomedical engineering - Abstract
Dopamine (DA) is one kind of neurotransmitter in central nervous system which is indicator of neural disease. For this reason, determination of DA concentration in central nervous system is very important for early diagnosis of neural disease. In this study, we designed micro electrode array and fabricated by MEMS technology. Furthermore, we fabricated 3-D conducting nanostructure on electrode surface for enhanced sensitivity and selectivity due to increased surface area. Compared with macro and normal micro electrode, the 3-D nanostructure modified micro electrode shows better electrical performance. These surface modified pin type electrode was applied to detect low concentration of DA and successfully detect various concentration of DA from 100 μM to 1 μM with linear relationship in the presence of ascorbic acid and uric acid. From these results, our newly designed electrode shows possibility to be applied as brain biosensor for neural disease diagnosis such as Parkinson's diseases.
- Published
- 2016
42. Hybrid energy harvester based on piezoelectric and triboelectric effects
- Author
-
Kwang-Seok Yun and Jungyong Park
- Subjects
Materials science ,Polydimethylsiloxane ,020208 electrical & electronic engineering ,Hinge ,Nanogenerator ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Piezoelectricity ,Stress (mechanics) ,chemistry.chemical_compound ,chemistry ,0202 electrical engineering, electronic engineering, information engineering ,Composite material ,0210 nano-technology ,Triboelectric effect ,Mechanical energy ,Voltage - Abstract
This paper describes an energy harvester which uses triboelectric and piezoelectric effect simultaneously to harvest the mechanical energy. The vertical vibration is converted into horizontal force through the hinge structure to apply stress on woven piezoelectric films. In addition, the vertical motion induces the triboelectric energy generation due to the contact between top plate and woven structures. The nano structured metal and polydimethylsiloxane (PDMS) surfaces were used to enhance the triboelectric effect. The maximum output voltage of 24 Vp-p and 291 Vp-p was simultaneously obtained from the triboelectric and piezoelectric effects, respectively, during the device operation at 9Hz.
- Published
- 2016
43. Magnetic alignment of co-doped zinc oxide nanorods for stretchable energy harvester
- Author
-
Sanghoon Kim and Kwang-Seok Yun
- Subjects
Materials science ,business.industry ,Graphene ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Zinc ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,law.invention ,Magnetic field ,chemistry ,Ferromagnetism ,law ,Electrical resistivity and conductivity ,Electrode ,Optoelectronics ,Nanorod ,0210 nano-technology ,business - Abstract
In this paper, we propose a skin attachable piezoelectric energy harvester which was implemented by using magnetic alignment of cobalt (Co)-doped zinc oxide nanorods (ZnO NRs) to enhance the piezoelectric effect. Co-doped ZnO NRs with ferromagnetic property can be easily obtained by hydrothermal process, and their uni-directional alignment can be obtained by applying external magnetic field. In addition, double layers of platinum (Pt) and graphene were deposited on the surface as a flexible and stretchable electrode with high electric conductivity. The maximum open-circuit voltage of 17.4 Vp-p and short-circuit current of 0.26 μA was obtained at 4 Hz folding/unfolding operations.
- Published
- 2016
44. Patterning of carbon nanotube films on PDMS using SU-8 microstructures
- Author
-
Kwang-Seok Yun and Dong-Il Kim
- Subjects
Fabrication ,Materials science ,Polydimethylsiloxane ,business.industry ,Nanotechnology ,Carbon nanotube ,Conductivity ,Condensed Matter Physics ,Microstructure ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,chemistry ,Hardware and Architecture ,Gauge factor ,law ,Optoelectronics ,Electrical and Electronic Engineering ,Photolithography ,business ,Sheet resistance - Abstract
In this paper, we propose a simple and low-cost fabrication technique for patterning carbon nanotube (CNT) films on polydimethylsiloxane (PDMS), which can be used in flexible sensors and electronics. We demonstrate CNT patterning on both recessed and flat PDMS surfaces using a standard photolithography method. By this proposed technique, we were able to fabricate a CNT film, having a high flexibility and good conductivity, on a PDMS surface. A CNT pattern with a minimum feature resolution of 150 μm was obtained using the proposed fabrication technique. The sheet resistance of the CNT film on the PDMS surface was determined to be in the 100–280 Ω/sq range. The thickness and resultant resistivity of the CNT film can be easily controlled by controlling just the spray duration. Furthermore, the gauge factor of the proposed device is higher than that of metal and it increases as the thickness of the CNT film increases.
- Published
- 2012
45. A High-Speed Single Crystal Silicon AFM Probe Integrated with PZT Actuator for High-Speed Imaging Applications
- Author
-
Kwang-Seok Yun, Il-Joo Cho, and Hyo-Jin Nam
- Subjects
Cantilever ,Materials science ,Silicon ,Atomic force microscopy ,business.industry ,Pzt actuator ,chemistry.chemical_element ,Nanotechnology ,chemistry ,Deflection (engineering) ,Optoelectronics ,Wafer ,Electrical and Electronic Engineering ,Boron ,Actuator ,business - Abstract
A new high speed AFM probe has been proposed and fabricated. The probe is integrated with PZT actuated cantilever realized in bulk silicon wafer using heavily boron doped silicon as an etch stop layer. The cantilever thickness can be accurately controlled by the boron diffusion process. Thick SCS cantilever and integrated PZT actuator make it possible to be operated at high speed for fast imaging. The resonant frequency of the fabricated probe is 92.9 ㎑ and the maximum deflection is 5.3 ㎛ at 3 V. The fabricated probe successfully measured the surface of standard sample in an AFM system at the scan speed of 600㎛/sec
- Published
- 2011
46. Capacitive tactile sensor array for touch screen application
- Author
-
Hongki Kim, Kwang-Seok Yun, and Seung-Gun Lee
- Subjects
Materials science ,business.industry ,Capacitive sensing ,Force gauge ,Metals and Alloys ,Bend radius ,Substrate (printing) ,Condensed Matter Physics ,Capacitance ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Instrumentation ,Sensitivity (electronics) ,Image resolution ,Tactile sensor - Abstract
In this paper, we propose and demonstrate a transparent and flexible capacitive tactile sensor which is designed for multi-touch screen application with force sensing. A sensor module is composed of 2D array tactile cells with a spatial resolution of 2 mm to measure the touch force at multiple positions. The device is fabricated by using transparent materials on a transparent plastic substrate. The optical transmittance of the fabricated tactile sensor is approximately 86% in the visible wavelength region, and the maximum bending radius is approximately 30 mm. The cell size is 1 mm × 1 mm, and the initial capacitance of each cell is approximately 900 fF. The tactile response of a cell is measured with a commercial force gauge having a resolution of 1 mN. The sensitivity of a cell is 4%/mN within the full scale range of 0.3 N.
- Published
- 2011
47. Single-cell manipulation on microfluidic chip by dielectrophoretic actuation and impedance detection
- Author
-
Hyunjin Park, Kwang-Seok Yun, and Dong-Il Kim
- Subjects
Materials science ,Fabrication ,business.industry ,Microfluidics ,Metals and Alloys ,Analytical chemistry ,Microbead (research) ,Dielectrophoresis ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Threshold voltage ,Electrode ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Biochip ,business ,Instrumentation ,Electrical impedance - Abstract
This paper presents the design, fabrication, and characterization of a microfluidic biochip with integrated actuation electrodes used to manipulate a cell and a microbead by dielectrophoresis and sensing electrodes to detect the trapping by using the impedance detection method. Combining deflective dielectrophoretic barriers with controlled pressure-driven liquid flows allows the accurate control of a cell/microbead in suspensions. The threshold voltage for microbead trapping was experimentally verified at various flow rates. The impedance change caused by the blockage of the electrical conducting path between sensing electrodes with the trapping of an MCF7 cell and a polystyrene microbead was measured. The impedance before the trapping of an MCF7 cell was 10.9 MΩ at 1 kHz and increased to 12 MΩ when the cell was placed between sensing electrodes.
- Published
- 2010
48. Multifunctional microwell plate for on-chip cell and microbead-based bioassays
- Author
-
Kwang-Seok Yun, Dohoon Lee, Euisik Yoon, and Hak-Sung Kim
- Subjects
Materials science ,Polydimethylsiloxane ,Microwell Plate ,Metals and Alloys ,Nanotechnology ,Microbead (research) ,Lab-on-a-chip ,Cell chip ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Materials Chemistry ,Electrical and Electronic Engineering ,Instrumentation ,Microfabrication - Abstract
This paper reports on a multifunctional microwell plate developed for lab-on-a-chip applications, such as high-throughput cell assay, drug screening, and microbead-based analyses. The proposed device was designed to provide three consecutive functions: the autonomous capture of biomaterials into multiple microwells in a two-dimensional array; active physical sealing of the microwells for isolation; and specific chemical injection into each microwell. The device was implemented with microfabrication technology using polydimethylsiloxane (PDMS) structures on a silicon or glass substrate. The multiple functions of the microwell plate were successfully demonstrated in an experiment using microbeads. The parallel positioning of live cells (CHO DG44) in multiple microwell arrays was achieved, as well as the independent injection of foreign solution into a specific target cell. Also the proposed microwell plate was utilized to capture microbeads, for antibody injection into each microwell, for quantum dot (QD) injection, and for fluorescence detection for a feasible demonstration of a microbead-based assay.
- Published
- 2009
49. Multifunctional Woven Structure Operating as Triboelectric Energy Harvester, Capacitive Tactile Sensor Array, and Piezoresistive Strain Sensor Array
- Author
-
Cheolmin Park, Kwang-Seok Yun, Kihong Kim, and Giyoung Song
- Subjects
Materials science ,Capacitive sensing ,02 engineering and technology ,Thread (computing) ,lcsh:Chemical technology ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Article ,Analytical Chemistry ,Sensor array ,smart fabric ,Vertical direction ,lcsh:TP1-1185 ,strain sensors ,triboelectric energy harvester ,capacitive sensors ,tactile sensors ,Electrical and Electronic Engineering ,Instrumentation ,Triboelectric effect ,Resistive touchscreen ,business.industry ,Electrical engineering ,021001 nanoscience & nanotechnology ,Piezoresistive effect ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Optoelectronics ,0210 nano-technology ,business ,Tactile sensor - Abstract
This paper presents a power-generating sensor array in a flexible and stretchable form. The proposed device is composed of resistive strain sensors, capacitive tactile sensors, and a triboelectric energy harvester in a single platform. The device is implemented in a woven textile structure by using proposed functional threads. A single functional thread is composed of a flexible hollow tube coated with silver nanowires on the outer surface and a conductive silver thread inside the tube. The total size of the device is 60 × 60 mm² having a 5 × 5 array of sensor cell. The touch force in the vertical direction can be sensed by measuring the capacitance between the warp and weft functional threads. In addition, because silver nanowire layers provide piezoresistivity, the strain applied in the lateral direction can be detected by measuring the resistance of each thread. Last, with regard to the energy harvester, the maximum power and power density were measured as 201 μW and 0.48 W/m², respectively, when the device was pushed in the vertical direction.
- Published
- 2017
50. Microfluidic chip for characterization of mechanical property of cell by using impedance measurement
- Author
-
Jungyul Park, Kwang-Seok Yun, Sangho Lee, Sung-Sik Chio, Eunpyo Choi, and Dong-Il Kim
- Subjects
Materials science ,business.industry ,technology, industry, and agriculture ,Stiffness ,Substrate (electronics) ,Lab-on-a-chip ,law.invention ,Characterization (materials science) ,Cell membrane ,Membrane ,medicine.anatomical_structure ,law ,Electrode ,medicine ,Electronic engineering ,Optoelectronics ,medicine.symptom ,business ,Electrical impedance - Abstract
In this paper we propose a microfluidic chip that measures the mechanical stiffness of cell membrane using impedance measurement. The microfluidic chip is composed of PDMS channel and a glass substrate with electrode. The proposed device uses patch-clamp technique to capture and deform a target cell and measures impedance of deformed cells. We demonstrated that the impedance increased after the membrane stretched and blocked the channel.
- Published
- 2009
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