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경사입사 초음파에서 계면 접촉 음향 비선형성에 의해 발생한 고조파의 영상화
윤동석(Dongseok Yun),최성호(Sungho Choi),김정석(Chungseok Kim),장경영(Kyung-Young Jhang) 한국비파괴검사학회 2012 한국비파괴검사학회지 Vol.32 No.4
본 연구에서는 닫힘균열의 조기발견을 위해서 경사입사 초음파를 이용하여 계면 접촉 음향 비선형성에 의해 발생한 고조파를 영상화하고자 한다. 알루미늄 시편 두 개를 접촉하여 고체-고체 접촉계면을 만들어 닫힘균열을 모사하였고, 접촉계면 압력에 따른 초음파의 음향 비선형을 영상화하였다. 영상화 기법으로는 sampling phased array(SPA)와 synthetic aperture focusing technique(SAFT) 기법을 사용하였다. 접촉계면 압력이 증가하면서 기본 주파수의 성분은 감소하였고 2차 고조파 성분은 증가하다가 닫힘균열로 모사된 부분에서 가장 큰 값을 나타내고 이후에는 감소하였다. 결과적으로 접촉계면에서 음향 비선형성에 의해 발생한 고조파를 영상화 하는 것이 가능하며 이는 초기균열의 조기발견에 적용 가능할 것으로 기대 된다. The objective of this study is to image the harmonic wave generated by contact acoustic nonlinearity in obliquely incident ultrasonic wave for early detection of closed cracks. A closed crack has been simulated by contacting two aluminum block specimens producing solid-solid contact interfaces and then acoustic nonlinearity has been imaged with contact pressure. Sampling phased array(SPA) and synthetic aperture focusing technique(SAFT) are used for imaging techniques. The amplitude of the fundamental frequency decreased with appling pressure. But, the amplitude of second harmonic increased with pressure and was a maximum amplitude at the simulation point of closed crack. Then, the amplitude of second harmonic decreased. As a result, harmonic imaging of contact acoustic nonlinearity is possible and it is expected to be apply for early detection of initial cracks.
Review of Analog Neuron Devices for Hardware-based Spiking Neural Networks
Dongseok Kwon,Sung Yun Woo,Jong Ho Lee 대한전자공학회 2022 Journal of semiconductor technology and science Vol.22 No.2
To process data operations more efficiently in deep neural networks (DNNs), studies on spiking neural networks (SNNs) have been conducted. In the reported literature, CMOS neuron circuits that mimic the biological behavior of an integrate-and-fire function of neurons have been mainly studied. Because conventional neuronal circuits need to be improved in terms of area and energy consumption, neuron devices with memory functions such as resistive random access memory (RRAM), phase-change random access memory (PCRAM), magnetic random access memory (MRAM), floating body FETs, and ferroelectric FETs have been emerged to replace a membrane capacitor and trigger device in the conventional neuron circuits. In this review article, neuron devices that can increase the integration density of conventional neuronal circuits and reduce power consumption are reviewed. These devices are expected to play an important role in future neuromorphic systems.
Electrothermal Local Annealing via Graphite Joule Heating on Two-Dimensional Layered Transistors
Yun, Yoojoo,Park, Jeongmin,Kim, Hyun,Bae, Jung Jun,Joo, Min-Kyu,Suh, Dongseok American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.30
<P>A simple but powerful device platform for electrothermal local annealing (ELA) via graphite Joule heating on the surface of transition-metal dichalcogenide, is suggested here to sustainably restore intrinsic electrical properties of atomically thin layered materials. Such two-dimensional materials are easily deteriorated by undesirable surface/interface adsorbates and are screened by a high metal-to-semiconductor contact resistance. The proposed ELA allows one to expect a better electrical performance such as an excess electron doping, an enhanced carrier mobility, and a reduced surface traps in a monolayer molybdenum disulfide (MoS<SUB>2</SUB>)/graphite heterostructure. The thermal distribution of local heating measured by an infrared thermal microscope and estimated by a finite element calculation shows that the annealing temperature reaches up to >400 K at ambient condition and the high efficiency of site-specific annealing is demonstrated unlike the case of conventional global thermal annealing. This ELA platform can be further promoted as a practical gas sensor application. From an O<SUB>2</SUB> cycling test and a low-frequency noise spectroscopy, the graphite on top of the MoS<SUB>2</SUB> continuously recovers its initial condition from surface adsorbates. This ELA technique significantly improves the stability and reliability of its gas sensing capability, which can be expanded in various nanoscale device applications.</P> [FIG OMISSION]</BR>
Structure variation effects on device reliability of single photon avalanche diodes
Shin, Dongseok,Park, Byungchoul,Chae, Youngcheol,Yun, Ilgu Elsevier 2017 Microelectronics reliability Vol.76 No.-
<P>Single photon avalanche diode (SPAD) is one of the promising candidates among photodetectors due to its high sensitivity and accuracy. Along with the existing custom compound avalanche diodes, SPADs fabricated in CMOS technology have been suggested and studied widely due to its advantage in manufacturing cost and system integration capability. Since SPAD is the core device in photodetector module and can be applied to the usage of the autonomous driving system, the reliability of SPADs should be addressed and studied. In this paper, the device reliability and temperature dependence of SPADs varying the different device structures are investigated and the relationship between device structure and device characteristics is also discussed with modeling and simulation. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Synaptic device using a floating fin-body MOSFET with memory functionality for neural network
Woo, Sung Yun,Choi, Kyu-Bong,Lim, Suhwan,Lee, Sung-Tae,Kim, Chul-Heung,Kang, Won-Mook,Kwon, Dongseok,Bae, Jong-Ho,Park, Byung-Gook,Lee, Jong-Ho Pergamon Press 2019 Solid-state electronics Vol.156 No.-
<P><B>Abstract</B></P> <P>We fabricate a floating fin-body MOSFET with charge trap layer on p-type (1 0 0) Si wafer and investigate the characteristics of the fabricated device as a synaptic device. To implement the long-term potentiation (LTP) and long-term depression (LTD), the change in conductance of the proposed device is investigated by adjusting the amount of charge in charge trap layer. A pair of synaptic device with these LTP and LTD is suggested to express the synaptic weight update in a multi-layer neural network. In addition, we show suitable weight-updating method using the proposed devices for implementing multi-layer neural networks. A 3-layer perceptron network consisted of 784 input, 200 hidden, and 10 output neurons was simulated using the conductance response of the proposed devices. In pattern recognition for 28 × 28 MNIST handwritten patterns, high learning performance with a classification accuracy of 95.74% is obtained when the unidirectional weight update method (B) is used.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated a floating fin-body MOSFET with charge trap layer and investigated the characteristics of the fabricated device as a synaptic device. </LI> <LI> To implement the LTP and LTD, the change in conductance of the proposed device is investigated by adjusting the amount of charge in charge trap layer. </LI> <LI> A pair of synaptic device with these LTP and LTD is suggested to express the synaptic weight update for on-chip training neural network. </LI> </UL> </P>
Feasibility of MFC (Macro-Fiber Composite) Transducers for Guided Wave Technique
Gang Ren,Dongseok Yun,Hogeon Seo,Minkyoo Song,Kyung-Young Jhang 한국비파괴검사학회 2013 한국비파괴검사학회지 Vol.33 No.3
Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.
Feasibility of MFC (Macro-Fiber Composite) Transducers for Guided Wave Technique
Ren, Gang,Yun, Dongseok,Seo, Hogeon,Song, Minkyoo,Jhang, Kyung-Young The Korean Society for Nondestructive Testing 2013 한국비파괴검사학회지 Vol.33 No.3
Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.