11 results on '"Woochan Lee"'
Search Results
2. Organic–Inorganic Hybrid Approach to Pulse Oximetry Sensors with Reliability and Low Power Consumption
- Author
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Tae Hyun Kim, Woochan Lee, Hyeonwoo Lee, Hyun Woo Lee, Seunghyup Yoo, Sungyeon Kim, Seung-Hee Lee, Marco Vinicio Alban, and Jinouk Song
- Subjects
Pulse oximetry ,Materials science ,medicine.diagnostic_test ,Power consumption ,Organic inorganic ,medicine ,Electrical and Electronic Engineering ,Hybrid approach ,Atomic and Molecular Physics, and Optics ,Reliability (statistics) ,Biotechnology ,Electronic, Optical and Magnetic Materials ,Reliability engineering - Published
- 2021
3. Maximum Efficiency Conditions Satisfying Power Regulation Constraints in Multiple-Receivers Wireless Power Transfer
- Author
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Won Lee, Woochan Lee, and Dukju Ahn
- Subjects
wireless power transfer ,magnetic resonance ,optimization ,Control and Optimization ,Renewable Energy, Sustainability and the Environment ,Energy Engineering and Power Technology ,Electrical and Electronic Engineering ,Engineering (miscellaneous) ,Computer Science::Information Theory ,Energy (miscellaneous) - Abstract
We propose the conditions for maximum overall efficiency at the constraint of satisfying asymmetric load power requirements for each receiver, for multiple-receivers wireless power transfer. Previously, the limitation of multiple-receiver analysis was that only the efficiency was maximized, whereas the requirements of load power were neglected. In many cases, conventional efficiency maximization assigns insufficient power to receivers far from the transmitter, while supplying excessive power to receivers near the transmitter. To resolve this limitation, we maximize the efficiency at the constraints of specified load power for each receiver. The proposed closed-form equation provides an optimum TX coil current amplitude, and the optimum load resistances of each receiver, to achieve the maximum efficiency at the load power regulation.
- Published
- 2022
4. Efficient, Load Independent and Self-Regulated Wireless Power Transfer with Multiple Loads for Long Distance IoT Applications
- Author
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Byunghun Lee, Woochan Lee, and Najam ul Hassan
- Subjects
Control and Optimization ,Computer science ,coupling coefficient ,coil design ,Energy Engineering and Power Technology ,wireless power transfer ,quality factor ,02 engineering and technology ,lcsh:Technology ,Resonator ,0202 electrical engineering, electronic engineering, information engineering ,Maximum power transfer theorem ,Wireless power transfer ,Electrical and Electronic Engineering ,Engineering (miscellaneous) ,Renewable Energy, Sustainability and the Environment ,business.industry ,lcsh:T ,020208 electrical & electronic engineering ,Electrical engineering ,020206 networking & telecommunications ,resonators ,Power (physics) ,Smart grid ,Electromagnetic coil ,Skin effect ,business ,Coupling coefficient of resonators ,Energy (miscellaneous) ,Voltage - Abstract
This paper proposes a wireless power transfer (WPT) system by placing repeater coils to transfer power to multiple loads for the internet of things (IoT) devices and sensors in smart grid applications. The proposed system intermediate resonators (repeaters) not only function as power relays to enhance the transfer distance but also supplies power to its load attached to them. Equal power distribution and load-independent characteristics were obtained without efficiency degradation when any one of the loads was changed during system operation. Identical high-quality factor coils were designed using Litz-wire to reduce the skin effect. The coil size was 15.5 cm × 15.5 cm and the four relays achieved total efficiency of 51.7%, delivering 2 W power and output voltage of 5 V to each load with a total power transfer distance of 62 cm.
- Published
- 2021
5. Wireless Power Transfer under Wide Distance Variation Using Dual Impedance Frequency
- Author
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Woochan Lee and Dukju Ahn
- Subjects
Materials science ,Computer Networks and Communications ,Acoustics ,lcsh:TK7800-8360 ,02 engineering and technology ,frequency splitting ,0202 electrical engineering, electronic engineering, information engineering ,Wireless power transfer ,Electrical and Electronic Engineering ,dual impedance ,Dual impedance ,Electrical impedance ,reflected resistance ,dual band ,020208 electrical & electronic engineering ,lcsh:Electronics ,020206 networking & telecommunications ,Power (physics) ,Coupling (computer programming) ,inductive power ,Hardware and Architecture ,Control and Systems Engineering ,Electromagnetic coil ,Signal Processing ,Multi-band device ,Coupling coefficient of resonators - Abstract
A dual-impedance operation, where coil impedance is controlled by operating frequency selection, is proposed to maintain optimum reflected impedance across coupling variation. More specifically, this work focuses on how high coupling between coils presents excessively high reflected resistance to transmitter (Tx) inverters, degrading the efficiency and output power of the inverter. To overcome this problem, the proposed system is equipped with dual-impedance coil and selects high- or low-impedance coil based on the ability to operate both at 200 kHz and 6.78 MHz frequencies. The reactive impedances of 6.78 MHz coils are designed to be higher than that of 200 kHz coils. Since the reflected resistance is proportional to the coil impedances and coupling squared, at close distance with high coupling coefficient, 200 kHz coils with low coil impedances are activated to prevent an excessive rise in reflected resistance. On the other hand, at large distance spacing with low coupling coefficient, 6.78 MHz coils with high coil impedances are activated so that sufficient reflected resistance is obtained even under the small coupling. The proposed system’s advantages are the high efficiency and the elimination of bulky mechanical relay switches. Measured efficiencies are 88.6–50% across 10 coupling variations.
- Published
- 2020
6. Effect of Cutaneous Feedback on the Perception of Virtual Object Weight during Manipulation
- Author
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Bukun Son, Woochan Lee, Ilhwan Han, and Jaeyoung Park
- Subjects
0209 industrial biotechnology ,genetic structures ,Computer science ,media_common.quotation_subject ,lcsh:Medicine ,Tactile sensation ,Weight Perception ,02 engineering and technology ,Stimulus (physiology) ,Virtual reality ,Article ,Tactile stimuli ,03 medical and health sciences ,020901 industrial engineering & automation ,0302 clinical medicine ,Human–computer interaction ,Perception ,lcsh:Science ,media_common ,Haptic technology ,Multidisciplinary ,lcsh:R ,Kinesthetic learning ,Object (computer science) ,Electrical and electronic engineering ,Mechanical engineering ,body regions ,Virtual image ,Touch Perception ,lcsh:Q ,Haptic perception ,030217 neurology & neurosurgery - Abstract
Haptic interface technologies for virtual reality applications have been developed to increase the reality and manipulability of a virtual object by creating a diverse tactile sensation. Most evaluation of the haptic technologies, however, have been limited to the haptic perception of the tactile stimuli via static virtual objects. Noting this, we investigated the effect of lateral cutaneous feedback, along with kinesthetic feedback on the perception of virtual object weight during manipulation. We modeled the physical interaction between a participant’s finger avatars and virtual objects. The haptic stimuli were rendered with custom-built haptic feedback systems that can provide kinesthetic and lateral cutaneous feedback to the participant. We conducted two virtual object manipulation experiments, 1. a virtual object manipulation with one finger, and 2. the pull-out and lift-up of a virtual object grasped with a precision grip. The results of Experiment 1 indicate that the participants felt the virtual object rendered with lateral cutaneous feedback significantly heavier than with only kinesthetic feedback (p mref = 100 and 200 g). Similarly, the participants of Experiment 2 felt the virtual objects significantly heavier when lateral cutaneous feedback was available (p mref = 100, 200, and 300 g). Therefore, the additional lateral cutaneous feedback to the force feedback led the participants to feel the virtual object heavier than without the cutaneous feedback. The results also indicate that the contact force applied to a virtual object during manipulation can be a function of the perceived object weight (p = 0.005 for Experiment 1 and p = 0.02 for Experiment 2).
- Published
- 2020
7. Energy-Efficient Wireless Hopping Sensor Relocation Based on Prediction of Terrain Conditions
- Author
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Woochan Lee, Moonseong Kim, and Sooyeon Park
- Subjects
relocation protocol ,Computer Networks and Communications ,Computer science ,Real-time computing ,lcsh:TK7800-8360 ,Terrain ,02 engineering and technology ,wireless sensor networks (WSNs) ,0202 electrical engineering, electronic engineering, information engineering ,Wireless ,Electrical and Electronic Engineering ,Protocol (object-oriented programming) ,energy efficient protocol ,020203 distributed computing ,hopping sensor ,business.industry ,lcsh:Electronics ,020206 networking & telecommunications ,simulation ,internet of things (IoTs) ,Hardware and Architecture ,Control and Systems Engineering ,Signal Processing ,mobile sensor ,business ,Energy (signal processing) ,Efficient energy use - Abstract
It is inevitable for data collection that IoT sensors are distributed to interested areas. However, not only the proper placement of sensors, but also the replacement of sensors that have run out of energy is very difficult. As a remedy, wireless charging systems for IoT sensors have been researched recently, but it is apparent that the availability of charging system is limited especially for IoT sensors scattered in rugged terrain. Thus, it is important that the sensor relocation models to recover sensing holes employ energy-efficient scheme. While there are various methods in the mobile model of wireless sensors, well-known wheel-based movements in rough areas are hard to achieve. Thus, research is ongoing in various areas of the hopping mobile model in which wireless sensors jump. Many past studies about hopping sensor relocation assume that all sensor nodes are aware of entire network information throughout the network. These assumptions do not fit well to the actual environment, and they are nothing but classical theoretical research. In addition, the physical environment (sand, mud, etc.) of the area in which the sensor is deployed can change from time to time. In this paper, we overcome the theoretical-based problems of the past researches and propose a new realistic hopping sensor relocation protocol considering terrain conditions. Since the status of obstacles around the sensing hole is unknown, the success rate of the hopping sensor relocation is used to predict the condition of the surrounding environment. Also, we are confident that our team is uniquely implementing OMNeT++ (Objective Modular Network Testbed in C++) simulation in the hopping sensor relocation protocol to reflect the actual communication environment. Simulations have been performed on various obstacles for performance evaluation and analysis, and we are confident that better energy efficiency with later appearance of sensing holes can be achieved compared to well-known relocation protocols.
- Published
- 2019
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8. A Real-Time Wearable Physiological Monitoring System for Home-Based Healthcare Applications
- Author
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Jin-Woo Jeong, Woochan Lee, and Young-Joon Kim
- Subjects
ECG/EMG sensing ,Home Environment ,Chemical technology ,rehabilitation training ,Signal Processing, Computer-Assisted ,TP1-1185 ,wireless communication ,Biochemistry ,Article ,Atomic and Molecular Physics, and Optics ,Analytical Chemistry ,Electrocardiography ,Wearable Electronic Devices ,physiological monitor ,smart wearable device ,Humans ,Electrical and Electronic Engineering ,Delivery of Health Care ,Instrumentation ,Monitoring, Physiologic - Abstract
The acquisition of physiological data are essential to efficiently predict and treat cardiac patients before a heart attack occurs and effectively expedite motor recovery after a stroke. This goal can be achieved by using wearable wireless sensor network platforms for real-time healthcare monitoring. In this paper, we present a wireless physiological signal acquisition device and a smartphone-based software platform for real-time data processing and monitor and cloud server access for everyday ECG/EMG signal monitoring. The device is implemented in a compact size (diameter: 30 mm, thickness: 4.5 mm) where the biopotential is measured and wirelessly transmitted to a smartphone or a laptop for real-time monitoring, data recording and analysis. Adaptive digital filtering is applied to eliminate any interference noise that can occur during a regular at-home environment, while minimizing the data process time. The accuracy of ECG and EMG signal coverage is assessed using Bland–Altman analysis by comparing with a reference physiological signal acquisition instrument (RHS2116 Stim/Recording System, Intan). Signal coverage of R-R peak intervals showed almost identical outcome between this proposed work and the RHS2116, showing a mean difference in heart rate of 0.15 ± 4.65 bpm and a Wilcoxon’s p value of 0.133. A 24 h continuous recording session of ECG and EMG is conducted to demonstrate the robustness and stability of the device based on extended time wearability on a daily routine.
- Published
- 2021
9. Ping-Pong Free Advanced and Energy Efficient Sensor Relocation for IoT-Sensory Network
- Author
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Woochan Lee, Moonseong Kim, and Sooyeon Park
- Subjects
relocation protocol ,ping-pong problem ,Computer science ,Big data ,Real-time computing ,02 engineering and technology ,lcsh:Chemical technology ,Biochemistry ,Article ,Analytical Chemistry ,Scheduling (computing) ,Header ,0202 electrical engineering, electronic engineering, information engineering ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,sensory data networking ,Instrumentation ,energy-efficient protocol ,mobile IoT ,020203 distributed computing ,hopping sensor ,business.industry ,020206 networking & telecommunications ,Energy consumption ,simulation ,Atomic and Molecular Physics, and Optics ,Internet of Things ,business ,Efficient energy use - Abstract
With the growing interest in big data technology, mobile IoT devices play an essential role in data collection. Generally, IoT sensor nodes are randomly distributed to areas where data cannot be easily collected. Subsequently, when data collection is impossible (i.e., sensing holes occurrence situation) due to improper placement of sensors or energy exhaustion of sensors, the sensors should be relocated. The cluster header in the sensing hole sends requests to neighboring cluster headers for the sensors to be relocated. However, it can be possible that sensors in the specific cluster zones near the sensing hole are continuously requested to move. With this knowledge, there can be a ping-pong problem, where the cluster headers in the neighboring sensing holes repeatedly request the movement of the sensors in the counterpart sensing hole. In this paper, we first proposed the near-uniform selection and movement scheme of the sensors to be relocated. By this scheme, the energy consumption of the sensors can be equalized, and the sensing capability can be extended. Thus the network lifetime can be extended. Next, the proposed relocation protocol resolves a ping-pong problem using queues with request scheduling. Another crucial contribution of this paper is that performance was analyzed using the fully-customed OMNeT++ simulator to reflect actual environmental conditions, not under over-simplified artificial network conditions. The proposed relocation protocol demonstrates a uniform and energy-efficient movement with ping-pong free capability.
- Published
- 2020
10. Fast Structure-Aware Direct Time-Domain Finite-Element Solver for the Analysis of Large-Scale On-Chip Circuits
- Author
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Dan Jiao and Woochan Lee
- Subjects
Tridiagonal matrix ,Computer science ,Industrial and Manufacturing Engineering ,Electronic, Optical and Magnetic Materials ,Computational science ,Reduction (complexity) ,Computer Science::Hardware Architecture ,Electronic engineering ,Single-core ,System on a chip ,Time domain ,Electrical and Electronic Engineering ,Scaling ,Network analysis ,Electronic circuit - Abstract
A fast time-domain finite-element algorithm is developed for the analysis and the design of very large-scale on-chip circuits. The structure specialty of on-chip circuits, such as Manhattan geometry and layered permittivity, is preserved in the proposed algorithm. As a result, the large-scale matrix solution encountered in the 3-D circuit analysis is turned into a simple scaling of the solution of a small 1-D tridiagonal matrix, which can be obtained in linear (optimal) complexity with negligible cost. Furthermore, the time step size is not sacrificed, and the total number of time steps to be simulated is also significantly reduced, thus achieving a total cost reduction in the CPU time. Applications to the simulation of very large-scale on-chip circuit structures on a single core have demonstrated the superior performance of the proposed method.
- Published
- 2015
11. Energy and Distance-Aware Hopping Sensor Relocation for Wireless Sensor Networks
- Author
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Moonseong Kim, Sooyeon Park, and Woochan Lee
- Subjects
relocation protocol ,Computer science ,Internet of Things (IoTs) ,Big data ,Real-time computing ,Topology (electrical circuits) ,02 engineering and technology ,lcsh:Chemical technology ,01 natural sciences ,Biochemistry ,Article ,energy and distance-aware relocation protocol ,Analytical Chemistry ,0202 electrical engineering, electronic engineering, information engineering ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,Instrumentation ,Protocol (object-oriented programming) ,hopping sensor ,business.industry ,010401 analytical chemistry ,Wireless Sensor Networks (WSNs) ,020206 networking & telecommunications ,jumping robot ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Sensor relocation ,Shortest path problem ,mobile sensor ,business ,Wireless sensor network ,Energy (signal processing) - Abstract
Recent advances in big data technology collecting and analyzing large amounts of valuable data have attracted a lot of attention. When the information in non-reachable areas is required, IoT wireless sensor network technologies have to be applied. Sensors fundamentally have energy limitations, and it is almost impossible to replace energy-depleted sensors that have been deployed in an inaccessible region. Therefore, moving healthy sensors into the sensing hole will recover the faulty sensor area. In rough surfaces, hopping sensors would be more appropriate than wheel-driven mobile sensors. Sensor relocation algorithms to recover sensing holes have been researched variously in the past. However, the majority of studies to date have been inadequate in reality, since they are nothing but theoretical studies which assume that all the topology in the network is known and then computes the shortest path based on the nonrealistic backing up knowledge&mdash, The topology information. In this paper, we first propose a distributed hopping sensor relocation protocol. The possibility of movement of the hopping sensor is also considered to recover sensing holes and is not limited to applying the shortest path strategy. Finally, a performance analysis using OMNeT++ has demonstrated the solidification of the excellence of the proposed protocol.
- Published
- 2019
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