• 센서학회지
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• 제29권1호
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• pp.19-26
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• 2020

Electrocardiogram (ECG) classification has become an essential task of modern day wearable devices, and can be used to detect cardiovascular diseases. State-of-the-art Artificial Intelligence (AI)-based ECG classifiers have been designed using various artificial neural networks (ANNs). Despite their high accuracy, ANNs require significant computational resources and power. Herein, three different ANNs have been compared: multilayer perceptron (MLP), convolutional neural network (CNN), and spiking neural network (SNN) only for the ECG classification. The ANN model has been developed in Python and Theano, trained on a central processing unit (CPU) platform, and deployed on a PYNQ-Z2 FPGA board to validate the model using a Jupyter notebook. Meanwhile, the hardware accelerator is designed with Overlay, which is a hardware library on PYNQ. For classification, the MIT-BIH dataset obtained from the Physionet library is used. The resulting ANN system can accurately classify four ECG types: normal, atrial premature contraction, left bundle branch block, and premature ventricular contraction. The performance of the ECG classifier models is evaluated based on accuracy and power. Among the three AI algorithms, the SNN requires the lowest power consumption of 0.226 W on-chip, followed by MLP (1.677 W), and CNN (2.266 W). However, the highest accuracy is achieved by the CNN (95%), followed by MLP (76%) and SNN (90%).

• 한국전자통신학회논문지
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• 제10권7호
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• pp.819-824
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• 2015

과거의 조형중심, 시스템 중심의 디자인에서 점차적으로 사용자를 배려하는 디자인 철학이 반영된 사용자 중심 디자인으로 패러다임이 변화하고, 특히 어떤 제품이나 서비스를 사용하는데 있어 최적의 경험을 제공하는 것을 목적으로 하는 UX디자인(User eXperience Design)의 중요성이 크게 인식되고 있다. 본 논문에서는 IoT시대에서 UX디자인이 고려해야할 변화 중에서 웨어러블의 기능에 영향이 적은 데이터를 기반으로 한 디자인 부분에 접근해 보았다. 다양하고 많은 데이터를 가진 기존 소셜커머스 앱의 레이아웃이 IoT디바이스의 인터페이스에서도 데이터 기반의 레이아웃과 유사하다고 생각하였다. 데이터 기반 앱을 모델로 레이아웃을 분석하여 UX디자인 의 구조를 정리하였다.

• 센서학회지
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• 제26권4호
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• pp.239-244
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• 2017

Noninvasive, cuffless, and continuous blood pressure (BP) monitoring is essential to prevent and control hypertension. A well-known existing method for this measurement is pulse transit time (PTT), which has been investigated by many researchers as a promising approach. However, the fundamental principle of the PTT method is based on the time interval taken by a pulse wave to propagate between the proximal and distal arterial sites. Consequently, this method needs an independent system with two devices placed at two different sites, which is a problem. Even though some studies attempted to synchronize the system, it is bulky and inconvenient by contemporary standards. To find a more sensitive method to be used in a BP measurement device, this study used radial electrical bioimpedance (REB) as a potential indicator for BP determination. Only one impedance plethysmography channel at the wrist is performed for demonstrating a ubiquitous BP wearable device. The experiment was evaluated on eight healthy subjects with the ambulatory BP monitor on the upper arm as a reference. The results demonstrated the potential of the proposed method by the correlation of estimated systolic (SBP) and diastolic (DBP) BP against the reference at $0.84{\pm}0.05$ and $0.83{\pm}0.05$, respectively. REB also tracked the DBP well with a root-mean-squared-error of $7.5{\pm}1.35mmHg$.

• 한국멀티미디어학회논문지
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• 제22권1호
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• pp.70-78
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• 2019

The smart festival costume developed in this study maximizes the design elements by attaching electronic device to clothing, and uses voice, movement, and light sensor to utilize as expression elements. In addition, as a way to maximize cultural exchanges between Korea and China, smart festival costume was developed by applying smart clothing technology to the traditional costumes of both countries. and it was exhibited for 10 days at the 'Andong International Mask Dance Festival 2018'. The smart festival costume has the effect of multiplying the dynamism and excitement of the festival by the use of colorful lighting and it has been evaluated that the experience of wearing traditional costume of both countries contributes greatly to promote international cultural exchange. However, since smart clothing is inconvenient to wear due to the use of electronic products, meticulous research for consumer safety is required for practical use. Smart devices is expected to utilize for the development of traditional culture resources and the fashion industry in the future.

• 센서학회지
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• 제30권1호
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• pp.20-24
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• 2021

The electrocardiogram (ECG) is one of the most extensively employed signals used to diagnose and predict cardiovascular diseases (CVDs). In recent years, several deep learning (DL) models have been proposed to improve detection accuracy. Among these, deep neural networks (DNNs) are the most popular, wherein the features are extracted automatically. Despite the increment in classification accuracy, DL models require exorbitant computational resources and power. This causes the mapping of DNNs to be slow; in addition, the mapping is challenging for a wearable device. Embedded systems have constrained power and memory resources. Therefore full-precision DNNs are not easily deployable on devices. To make the neural network faster and more power-efficient, spiking neural networks (SNNs) have been introduced for fewer operations and less complex hardware resources. However, the conventional SNN has low accuracy and high computational cost. Therefore, this paper proposes a new binarized SNN which modifies the synaptic weights of SNN constraining it to be binary (+1 and -1). In the simulation results, this paper compares the DL models and SNNs and evaluates which model is optimal for ECG classification. Although there is a slight compromise in accuracy, the latter proves to be energy-efficient.

• Elastomers and Composites
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• 제58권1호
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• pp.11-16
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• 2023

Electronic skin (e-skin), devices that are mounted on or attached to human skin, have advanced in recent times. Yet, the development of a power supply for e-skin remains a challenge. A stretchable thermoelectric generator is a promising power supply for the e-skin patches. It is a safe and semi-permanent energy harvesting device that uses body heat for generating power. Carbon nanotube (CNT) clays are used in energy-harvesting e-skin patches. In this study, we report improved thermoelectric performance of CNT clays by using chemical doping and physical blending of thermoelectric enhancers. The n-type and p-type thermoelectric enhancers increase electrical conductivity, leading to increased power factors of the thermoelectric CNT clays. The blend of CNT clays and enhancers is intrinsically stretchable up to 50% while maintaining its thermoelectric property.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• 한국인터넷방송통신학회논문지
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• 제23권4호
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• pp.171-176
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• 2023

21세기 현대사회에 있어서 이차전지 배터리(Battery)를 이용한 휴대용 전자제품은 계속해서 경량, 소형화되어가는 추세 속에서 있다. 그리고 이러한 추세와 더불어 우리는 몸에 착용할 수 있는 전자 장비를 이용하여 하루 일상생활에서 정보를 수집, 공유하는 4차 산업혁명 시대에 활동하고 있다. 따라서 소형 가전제품 및 디지털 기기를 사용하면서 재충전할 수 있는 이차전지 배터리의 역할은 점점 더 중요하게 증가하고 있다. 이러한 증가와 더불어 이차전지 배터리 성능시험은 특성, 수명, 고장진단, 재활용 등의 다양한 시험방법을 요구하고 있으며 있다. 또한 배터리의 안전과 적절한 기능을 보장하기 위한 배터리 테스트 시스템 구축과 이에 따른 지침 및 올바른 기본지식이 고려되고 있다. 따라서 본 논문에서는 배터리의 성능과 직접으로 연결된 시나리오별 충방전에 따른 이차전지 리튬이온(Li-ion) 배터리의 특성에 대해 살펴보고자 한다.

• 한국산학기술학회논문지
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• 제21권4호
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• pp.26-32
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• 2020

최근 웨어러블 장치와 IoT 기술들이 다양하게 개발 및 상용화되면서, 이에 발맞추어 다양한 종류의 센서 들이 개발되었고, 이런 새로운 종류의 센서들이 실생활에서 다양하게 접목되면서 다양한 응용 제품들이 개발되어 왔다. 새로운 센서 기술들이 현실화되면서 의학분야에서도 많이 적용되고 있으며, 특히 자기장 센서는 의학분야에서 다양한 목적으로 활용되어져 왔다. 본 논문에서는 소형의 영구자석과 이를 측정하기 위한 자기장 센서를 활용하여 손목의 재활 훈련이나 운동량을 측정하는 모델과 방법을 제시하고자 한다. 자석과 자기장 센서 사이에는 전기적인 선들의 연결이 없이도 자석과 자기장 센서 사이의 자기장을 측정할 수 있어, 이렇게 측정된 자기장 값들을 실제 자석과 자기장 센서간의 거리로 환산하여 측정할 수 있는 장점이 있다. 하지만, 자기장의 특징은 그 자체만으로도 비선형적인 자기장이 생성되기 때문에, 자기장 센서 패드와 손목동작의 비선형 모델로 인하여, 아주 복잡한 모델과 많은 계산이 요구하게 된다. 따라서 본 논문에서는 이런 구현상의 어려운 단점들을 보완하고 정확한 장기장센서 데이터를 측정하기 위하여, 손에 설치된 자석과 손목에 설치된 자기장 센서를 모델링하고 캘리브레이션하는 방법을 제안한다.

• 대한의용생체공학회:의공학회지
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• 제30권6호
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• pp.503-509
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• 2009

The development of technology has led to ubiquitous health care service, which enables many patients to receive medical services anytime and anywhere. For the ubiquitous health care environment, real-time measurement of biomedical signals is very important, and the medical instruments must be small and portable or wearable. So, such devices have been developed to measure biomedical signals. In this study, we develop the biomedical monitoring device which is sensing the PPG signal, one of the useful signal in the field of ubiquitous healthcare. We design a watch-like biomedical signal monitoring system without a finger probe to prevent the user's inconvenience. This system obtains the PPG from the radial artery using a sensor in the wrist band. But, new device developed in this paper is easy to get the motion artifacts. So, we proposed new algorithm removing the motion artifacts from the PPG signal. The method detects motion artifacts by changing the degree of brightness of the light source. If the brightness of the light source is reduced, the PPG pulses will disappear. When the PPG pulses have disappeared completely, the remaining signal is not the signal that results from the changing blood flow. We believe that this signal is the motion artifact and call it the noise reference signal. The motion artifacts are removed by subtracting the noise reference signal from the input signal. We apply this algorithm to the system, so we can stabilize the biomedical monitoring system we designed.